<?xml version="1.0" encoding="UTF-8"?>

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2025 Workiva-->
<!--r:7875a0b3-2429-479a-a62a-f19833ca663b,g:4bf32931-2ed7-482a-bbcc-be08e845220d-->
<link:linkbase xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd">
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member"/>
  <link:roleRef roleURI="http://www.icumed.com/role/CondensedConsolidatedBalanceSheets" xlink:type="simple" xlink:href="icui-20250930.xsd#CondensedConsolidatedBalanceSheets"/>
  <link:definitionLink xlink:role="http://www.icumed.com/role/CondensedConsolidatedBalanceSheets" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_887b9330-a2fa-488b-a3a6-49973cd2c985" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_32863f62-6b4a-45ca-9a69-5adb22331caa" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_887b9330-a2fa-488b-a3a6-49973cd2c985" xlink:to="loc_us-gaap_StatementTable_32863f62-6b4a-45ca-9a69-5adb22331caa" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementScenarioAxis_ade1540d-c92a-4d41-a592-5d58fcfdba0e" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_StatementScenarioAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_32863f62-6b4a-45ca-9a69-5adb22331caa" xlink:to="loc_srt_StatementScenarioAxis_ade1540d-c92a-4d41-a592-5d58fcfdba0e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioUnspecifiedDomain_ade1540d-c92a-4d41-a592-5d58fcfdba0e_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ScenarioUnspecifiedDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementScenarioAxis_ade1540d-c92a-4d41-a592-5d58fcfdba0e" xlink:to="loc_srt_ScenarioUnspecifiedDomain_ade1540d-c92a-4d41-a592-5d58fcfdba0e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioUnspecifiedDomain_a8387621-f313-4c5f-a7c6-79799366c7e4" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ScenarioUnspecifiedDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementScenarioAxis_ade1540d-c92a-4d41-a592-5d58fcfdba0e" xlink:to="loc_srt_ScenarioUnspecifiedDomain_a8387621-f313-4c5f-a7c6-79799366c7e4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsAbstract_8bcc56e8-60ee-47ee-a6cc-a696d846f95f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AssetsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_887b9330-a2fa-488b-a3a6-49973cd2c985" xlink:to="loc_us-gaap_AssetsAbstract_8bcc56e8-60ee-47ee-a6cc-a696d846f95f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsCurrentAbstract_7780c485-8ef1-4134-9427-03d54924f4de" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AssetsCurrentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_8bcc56e8-60ee-47ee-a6cc-a696d846f95f" xlink:to="loc_us-gaap_AssetsCurrentAbstract_7780c485-8ef1-4134-9427-03d54924f4de" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_b905f38e-d4c1-4f0b-acad-92de374599ee" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_7780c485-8ef1-4134-9427-03d54924f4de" xlink:to="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_b905f38e-d4c1-4f0b-acad-92de374599ee" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableNetCurrent_3648a3fb-1bda-40fa-80a4-42bd834abf50" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccountsReceivableNetCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_7780c485-8ef1-4134-9427-03d54924f4de" xlink:to="loc_us-gaap_AccountsReceivableNetCurrent_3648a3fb-1bda-40fa-80a4-42bd834abf50" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InventoryNet_7a50f074-4b03-4ff2-872b-358e53747ea9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InventoryNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_7780c485-8ef1-4134-9427-03d54924f4de" xlink:to="loc_us-gaap_InventoryNet_7a50f074-4b03-4ff2-872b-358e53747ea9" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PrepaidExpenseAndOtherAssetsCurrent_ab930e64-0e68-4bf8-9fd9-d46eccaff588" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PrepaidExpenseAndOtherAssetsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_7780c485-8ef1-4134-9427-03d54924f4de" xlink:to="loc_us-gaap_PrepaidExpenseAndOtherAssetsCurrent_ab930e64-0e68-4bf8-9fd9-d46eccaff588" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsOfDisposalGroupIncludingDiscontinuedOperation_6985435a-04f0-483b-b637-ce4dff16ee14" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AssetsOfDisposalGroupIncludingDiscontinuedOperation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_7780c485-8ef1-4134-9427-03d54924f4de" xlink:to="loc_us-gaap_AssetsOfDisposalGroupIncludingDiscontinuedOperation_6985435a-04f0-483b-b637-ce4dff16ee14" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsCurrent_dad61589-8325-4ce6-aaf9-26d3664b5db2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AssetsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_7780c485-8ef1-4134-9427-03d54924f4de" xlink:to="loc_us-gaap_AssetsCurrent_dad61589-8325-4ce6-aaf9-26d3664b5db2" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_1eabcb18-c3d2-4d88-a762-f2aa0609190b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_8bcc56e8-60ee-47ee-a6cc-a696d846f95f" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet_1eabcb18-c3d2-4d88-a762-f2aa0609190b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseRightOfUseAsset_c766c1ce-0399-4c9e-bf13-338159217dfe" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingLeaseRightOfUseAsset"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_8bcc56e8-60ee-47ee-a6cc-a696d846f95f" xlink:to="loc_us-gaap_OperatingLeaseRightOfUseAsset_c766c1ce-0399-4c9e-bf13-338159217dfe" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_de61f32e-521c-4160-bd05-cc58bbacf4f3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_Goodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_8bcc56e8-60ee-47ee-a6cc-a696d846f95f" xlink:to="loc_us-gaap_Goodwill_de61f32e-521c-4160-bd05-cc58bbacf4f3" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IntangibleAssetsNetExcludingGoodwill_24f46ae1-dcf7-436b-97a4-83d70bbc0341" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IntangibleAssetsNetExcludingGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_8bcc56e8-60ee-47ee-a6cc-a696d846f95f" xlink:to="loc_us-gaap_IntangibleAssetsNetExcludingGoodwill_24f46ae1-dcf7-436b-97a4-83d70bbc0341" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredIncomeTaxAssetsNet_66d31ba1-c60e-4b15-8997-84a64d7c8b12" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DeferredIncomeTaxAssetsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_8bcc56e8-60ee-47ee-a6cc-a696d846f95f" xlink:to="loc_us-gaap_DeferredIncomeTaxAssetsNet_66d31ba1-c60e-4b15-8997-84a64d7c8b12" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAssetsNoncurrent_cd13bd24-2e7e-46f1-a4b0-542a4c755401" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherAssetsNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_8bcc56e8-60ee-47ee-a6cc-a696d846f95f" xlink:to="loc_us-gaap_OtherAssetsNoncurrent_cd13bd24-2e7e-46f1-a4b0-542a4c755401" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityMethodInvestments_a91b9a2b-3d76-4605-aa20-2759d1a549af" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityMethodInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_8bcc56e8-60ee-47ee-a6cc-a696d846f95f" xlink:to="loc_us-gaap_EquityMethodInvestments_a91b9a2b-3d76-4605-aa20-2759d1a549af" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Assets_40d6f42c-fecc-4b8c-9ca3-f30a139251b0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_Assets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_8bcc56e8-60ee-47ee-a6cc-a696d846f95f" xlink:to="loc_us-gaap_Assets_40d6f42c-fecc-4b8c-9ca3-f30a139251b0" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_4ae45671-420e-43cc-9c01-bb25c7bbb25a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LiabilitiesAndStockholdersEquityAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_887b9330-a2fa-488b-a3a6-49973cd2c985" xlink:to="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_4ae45671-420e-43cc-9c01-bb25c7bbb25a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesCurrentAbstract_97b64405-4717-411f-9e4d-846332af036a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LiabilitiesCurrentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_4ae45671-420e-43cc-9c01-bb25c7bbb25a" xlink:to="loc_us-gaap_LiabilitiesCurrentAbstract_97b64405-4717-411f-9e4d-846332af036a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsPayableCurrent_d7d43742-678a-4909-a228-b0c1deaef99f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccountsPayableCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_97b64405-4717-411f-9e4d-846332af036a" xlink:to="loc_us-gaap_AccountsPayableCurrent_d7d43742-678a-4909-a228-b0c1deaef99f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccruedLiabilitiesCurrent_92772522-a799-4928-a2aa-e9472b597459" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccruedLiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_97b64405-4717-411f-9e4d-846332af036a" xlink:to="loc_us-gaap_AccruedLiabilitiesCurrent_92772522-a799-4928-a2aa-e9472b597459" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtCurrent_266af069-fe58-4372-aa04-92f1a31dacaf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongTermDebtCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_97b64405-4717-411f-9e4d-846332af036a" xlink:to="loc_us-gaap_LongTermDebtCurrent_266af069-fe58-4372-aa04-92f1a31dacaf" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccruedIncomeTaxesCurrent_0f450657-2a7f-4724-8d4a-8ccbe66a0e76" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccruedIncomeTaxesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_97b64405-4717-411f-9e4d-846332af036a" xlink:to="loc_us-gaap_AccruedIncomeTaxesCurrent_0f450657-2a7f-4724-8d4a-8ccbe66a0e76" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesOfDisposalGroupIncludingDiscontinuedOperation_8ab87b38-f17d-4eae-8578-752f2a0bd28b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LiabilitiesOfDisposalGroupIncludingDiscontinuedOperation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_97b64405-4717-411f-9e4d-846332af036a" xlink:to="loc_us-gaap_LiabilitiesOfDisposalGroupIncludingDiscontinuedOperation_8ab87b38-f17d-4eae-8578-752f2a0bd28b" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesCurrent_75b575c2-c717-4c22-a304-6b517870abd6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_97b64405-4717-411f-9e4d-846332af036a" xlink:to="loc_us-gaap_LiabilitiesCurrent_75b575c2-c717-4c22-a304-6b517870abd6" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtNoncurrent_f213f268-90bd-444d-b3c4-ef081068e006" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongTermDebtNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_4ae45671-420e-43cc-9c01-bb25c7bbb25a" xlink:to="loc_us-gaap_LongTermDebtNoncurrent_f213f268-90bd-444d-b3c4-ef081068e006" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherLiabilitiesNoncurrent_28063978-02bd-4c49-9d9f-b568ef431955" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherLiabilitiesNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_4ae45671-420e-43cc-9c01-bb25c7bbb25a" xlink:to="loc_us-gaap_OtherLiabilitiesNoncurrent_28063978-02bd-4c49-9d9f-b568ef431955" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredIncomeTaxLiabilitiesNet_9df3c34e-494c-40e1-b06d-1f5da43705b4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DeferredIncomeTaxLiabilitiesNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_4ae45671-420e-43cc-9c01-bb25c7bbb25a" xlink:to="loc_us-gaap_DeferredIncomeTaxLiabilitiesNet_9df3c34e-494c-40e1-b06d-1f5da43705b4" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccruedIncomeTaxesNoncurrent_70495f0d-3122-44ee-9d08-b49008fb0d48" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccruedIncomeTaxesNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_4ae45671-420e-43cc-9c01-bb25c7bbb25a" xlink:to="loc_us-gaap_AccruedIncomeTaxesNoncurrent_70495f0d-3122-44ee-9d08-b49008fb0d48" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommitmentsAndContingencies_8def25e5-f48e-480b-a8af-8d2dcd7df61b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommitmentsAndContingencies"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_4ae45671-420e-43cc-9c01-bb25c7bbb25a" xlink:to="loc_us-gaap_CommitmentsAndContingencies_8def25e5-f48e-480b-a8af-8d2dcd7df61b" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_c71eb5d0-feab-46c2-a7be-8a703e3b1fc3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_4ae45671-420e-43cc-9c01-bb25c7bbb25a" xlink:to="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_c71eb5d0-feab-46c2-a7be-8a703e3b1fc3" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertiblePreferredStockNonredeemableOrRedeemableIssuerOptionValue_7be78e1c-9601-458f-ae59-3a513f36b951" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConvertiblePreferredStockNonredeemableOrRedeemableIssuerOptionValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_c71eb5d0-feab-46c2-a7be-8a703e3b1fc3" xlink:to="loc_us-gaap_ConvertiblePreferredStockNonredeemableOrRedeemableIssuerOptionValue_7be78e1c-9601-458f-ae59-3a513f36b951" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockValue_4608b7ca-4c66-4341-90d1-27288e63daaa" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_c71eb5d0-feab-46c2-a7be-8a703e3b1fc3" xlink:to="loc_us-gaap_CommonStockValue_4608b7ca-4c66-4341-90d1-27288e63daaa" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalCommonStock_73f9220e-1aca-4676-b97b-5f715e24edcc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AdditionalPaidInCapitalCommonStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_c71eb5d0-feab-46c2-a7be-8a703e3b1fc3" xlink:to="loc_us-gaap_AdditionalPaidInCapitalCommonStock_73f9220e-1aca-4676-b97b-5f715e24edcc" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockValue_57a95035-6e1b-4a4b-addc-adbefea3c9a1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TreasuryStockValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_c71eb5d0-feab-46c2-a7be-8a703e3b1fc3" xlink:to="loc_us-gaap_TreasuryStockValue_57a95035-6e1b-4a4b-addc-adbefea3c9a1" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsAccumulatedDeficit_b0fc2096-6991-4819-8782-4de71b6524bc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetainedEarningsAccumulatedDeficit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_c71eb5d0-feab-46c2-a7be-8a703e3b1fc3" xlink:to="loc_us-gaap_RetainedEarningsAccumulatedDeficit_b0fc2096-6991-4819-8782-4de71b6524bc" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_e5fa209b-6597-4087-9ac0-e0f4ea6947ac" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_c71eb5d0-feab-46c2-a7be-8a703e3b1fc3" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_e5fa209b-6597-4087-9ac0-e0f4ea6947ac" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_73c38426-406d-48ba-98da-95af20fb5748" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_c71eb5d0-feab-46c2-a7be-8a703e3b1fc3" xlink:to="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_73c38426-406d-48ba-98da-95af20fb5748" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquity_984ef219-cde2-4120-978c-8bec3cfeccaa" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LiabilitiesAndStockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_4ae45671-420e-43cc-9c01-bb25c7bbb25a" xlink:to="loc_us-gaap_LiabilitiesAndStockholdersEquity_984ef219-cde2-4120-978c-8bec3cfeccaa" xlink:type="arc" order="8"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.icumed.com/role/CondensedConsolidatedStatementsofIncome" xlink:type="simple" xlink:href="icui-20250930.xsd#CondensedConsolidatedStatementsofIncome"/>
  <link:definitionLink xlink:role="http://www.icumed.com/role/CondensedConsolidatedStatementsofIncome" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_d2b53c20-e70d-48bc-975b-726733531b9c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_4ac4fd9d-8915-4b14-8c5a-948b57845d5f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_d2b53c20-e70d-48bc-975b-726733531b9c" xlink:to="loc_us-gaap_StatementTable_4ac4fd9d-8915-4b14-8c5a-948b57845d5f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_03e6d44f-8f94-488a-8b71-1f2f21808c6e" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_4ac4fd9d-8915-4b14-8c5a-948b57845d5f" xlink:to="loc_srt_ProductOrServiceAxis_03e6d44f-8f94-488a-8b71-1f2f21808c6e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_03e6d44f-8f94-488a-8b71-1f2f21808c6e_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_03e6d44f-8f94-488a-8b71-1f2f21808c6e" xlink:to="loc_srt_ProductsAndServicesDomain_03e6d44f-8f94-488a-8b71-1f2f21808c6e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_8eb39049-b0e7-4d14-9982-40a5c2803cac" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_03e6d44f-8f94-488a-8b71-1f2f21808c6e" xlink:to="loc_srt_ProductsAndServicesDomain_8eb39049-b0e7-4d14-9982-40a5c2803cac" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsAxis_70cb77f4-71ec-41b5-a23e-0ff6072b780f" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidationItemsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_4ac4fd9d-8915-4b14-8c5a-948b57845d5f" xlink:to="loc_srt_ConsolidationItemsAxis_70cb77f4-71ec-41b5-a23e-0ff6072b780f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_70cb77f4-71ec-41b5-a23e-0ff6072b780f_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidationItemsAxis_70cb77f4-71ec-41b5-a23e-0ff6072b780f" xlink:to="loc_srt_ConsolidationItemsDomain_70cb77f4-71ec-41b5-a23e-0ff6072b780f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_1ff8e701-d211-4c28-98b9-d953b0d3dcc5" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidationItemsAxis_70cb77f4-71ec-41b5-a23e-0ff6072b780f" xlink:to="loc_srt_ConsolidationItemsDomain_1ff8e701-d211-4c28-98b9-d953b0d3dcc5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingSegmentsMember_2e3783d8-69a4-4f09-bac8-08da34073b3f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingSegmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_1ff8e701-d211-4c28-98b9-d953b0d3dcc5" xlink:to="loc_us-gaap_OperatingSegmentsMember_2e3783d8-69a4-4f09-bac8-08da34073b3f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenuesAbstract_679e1a26-2c4d-49d6-92d0-5d2bcdd3f482" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenuesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_d2b53c20-e70d-48bc-975b-726733531b9c" xlink:to="loc_us-gaap_RevenuesAbstract_679e1a26-2c4d-49d6-92d0-5d2bcdd3f482" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_1a38d76e-dbe4-481a-aa9b-5f2217cbaa96" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenuesAbstract_679e1a26-2c4d-49d6-92d0-5d2bcdd3f482" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_1a38d76e-dbe4-481a-aa9b-5f2217cbaa96" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfRevenue_ef42dc40-dab2-46c3-a99b-4fdd0b43e19d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CostOfRevenue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenuesAbstract_679e1a26-2c4d-49d6-92d0-5d2bcdd3f482" xlink:to="loc_us-gaap_CostOfRevenue_ef42dc40-dab2-46c3-a99b-4fdd0b43e19d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GrossProfit_3a56b4f7-116f-4d78-aef5-c2a7ce75c018" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GrossProfit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenuesAbstract_679e1a26-2c4d-49d6-92d0-5d2bcdd3f482" xlink:to="loc_us-gaap_GrossProfit_3a56b4f7-116f-4d78-aef5-c2a7ce75c018" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingExpensesAbstract_21180b47-9b92-4103-98aa-8f57a88f5544" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingExpensesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_d2b53c20-e70d-48bc-975b-726733531b9c" xlink:to="loc_us-gaap_OperatingExpensesAbstract_21180b47-9b92-4103-98aa-8f57a88f5544" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SellingGeneralAndAdministrativeExpense_9a7ad1b2-b3aa-415a-8af5-a93372912436" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SellingGeneralAndAdministrativeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_21180b47-9b92-4103-98aa-8f57a88f5544" xlink:to="loc_us-gaap_SellingGeneralAndAdministrativeExpense_9a7ad1b2-b3aa-415a-8af5-a93372912436" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentExpense_aa82a40e-0014-4090-a7a9-c8aa8a05f0dd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ResearchAndDevelopmentExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_21180b47-9b92-4103-98aa-8f57a88f5544" xlink:to="loc_us-gaap_ResearchAndDevelopmentExpense_aa82a40e-0014-4090-a7a9-c8aa8a05f0dd" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_Restructuringandstrategictransaction_ea0f78ee-7a78-4f9a-8516-cd4621220476" xlink:href="icui-20250930.xsd#icui_Restructuringandstrategictransaction"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_21180b47-9b92-4103-98aa-8f57a88f5544" xlink:to="loc_icui_Restructuringandstrategictransaction_ea0f78ee-7a78-4f9a-8516-cd4621220476" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationContingentConsiderationArrangementsChangeInAmountOfContingentConsiderationLiability1_913d505f-a1b9-4c39-b381-4e012bd0c8d5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationContingentConsiderationArrangementsChangeInAmountOfContingentConsiderationLiability1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_21180b47-9b92-4103-98aa-8f57a88f5544" xlink:to="loc_us-gaap_BusinessCombinationContingentConsiderationArrangementsChangeInAmountOfContingentConsiderationLiability1_913d505f-a1b9-4c39-b381-4e012bd0c8d5" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingExpenses_d07dde20-afd7-4927-ad44-208f082caf1d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_21180b47-9b92-4103-98aa-8f57a88f5544" xlink:to="loc_us-gaap_OperatingExpenses_d07dde20-afd7-4927-ad44-208f082caf1d" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingIncomeLoss_0982b6b6-1dac-4fab-8b89-ddb31da1fa5e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_d2b53c20-e70d-48bc-975b-726733531b9c" xlink:to="loc_us-gaap_OperatingIncomeLoss_0982b6b6-1dac-4fab-8b89-ddb31da1fa5e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpense_2130dcd3-446f-4623-af40-c52a6420946c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InterestExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_d2b53c20-e70d-48bc-975b-726733531b9c" xlink:to="loc_us-gaap_InterestExpense_2130dcd3-446f-4623-af40-c52a6420946c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonoperatingIncomeExpense_59acc2d4-c80e-496e-ae3d-936597bcf839" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NonoperatingIncomeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_d2b53c20-e70d-48bc-975b-726733531b9c" xlink:to="loc_us-gaap_NonoperatingIncomeExpense_59acc2d4-c80e-496e-ae3d-936597bcf839" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainLossOnSaleOfBusiness_691db489-ab8b-46e4-a0c8-edcac73160cd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GainLossOnSaleOfBusiness"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_d2b53c20-e70d-48bc-975b-726733531b9c" xlink:to="loc_us-gaap_GainLossOnSaleOfBusiness_691db489-ab8b-46e4-a0c8-edcac73160cd" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_7780f448-9e5f-4ee2-868a-84cb1e801170" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_d2b53c20-e70d-48bc-975b-726733531b9c" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_7780f448-9e5f-4ee2-868a-84cb1e801170" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_1816d3f5-bad5-4149-b655-c07d9579090b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxExpenseBenefit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_d2b53c20-e70d-48bc-975b-726733531b9c" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefit_1816d3f5-bad5-4149-b655-c07d9579090b" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_NETLOSSFROMCONSOLIDATEDCOMPANIES_287f5ab3-9b58-46e0-97d4-04baa783b55c" xlink:href="icui-20250930.xsd#icui_NETLOSSFROMCONSOLIDATEDCOMPANIES"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_d2b53c20-e70d-48bc-975b-726733531b9c" xlink:to="loc_icui_NETLOSSFROMCONSOLIDATEDCOMPANIES_287f5ab3-9b58-46e0-97d4-04baa783b55c" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromEquityMethodInvestments_d2dd0a1a-34a3-4c58-b942-d343d4890801" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeLossFromEquityMethodInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_d2b53c20-e70d-48bc-975b-726733531b9c" xlink:to="loc_us-gaap_IncomeLossFromEquityMethodInvestments_d2dd0a1a-34a3-4c58-b942-d343d4890801" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProfitLoss_78039b7a-b5a3-45b5-8f86-7b55349c95d2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ProfitLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_d2b53c20-e70d-48bc-975b-726733531b9c" xlink:to="loc_us-gaap_ProfitLoss_78039b7a-b5a3-45b5-8f86-7b55349c95d2" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareAbstract_f657b1fc-4518-462a-b0d2-83050c262920" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EarningsPerShareAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_d2b53c20-e70d-48bc-975b-726733531b9c" xlink:to="loc_us-gaap_EarningsPerShareAbstract_f657b1fc-4518-462a-b0d2-83050c262920" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareBasic_a2fd8eab-9727-4cd1-85a5-6a3e0fc6cc5d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EarningsPerShareBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareAbstract_f657b1fc-4518-462a-b0d2-83050c262920" xlink:to="loc_us-gaap_EarningsPerShareBasic_a2fd8eab-9727-4cd1-85a5-6a3e0fc6cc5d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareDiluted_5ef5f013-d1f7-4211-b93a-160142f5cc00" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EarningsPerShareDiluted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareAbstract_f657b1fc-4518-462a-b0d2-83050c262920" xlink:to="loc_us-gaap_EarningsPerShareDiluted_5ef5f013-d1f7-4211-b93a-160142f5cc00" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract_ef79fea8-93df-4c15-85a4-49e49158ef7b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_d2b53c20-e70d-48bc-975b-726733531b9c" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract_ef79fea8-93df-4c15-85a4-49e49158ef7b" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_f47573d8-994d-4f30-ba33-e4680fc7fe8b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract_ef79fea8-93df-4c15-85a4-49e49158ef7b" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_f47573d8-994d-4f30-ba33-e4680fc7fe8b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_5759a60b-fd47-4894-8bdc-66c4df71117b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract_ef79fea8-93df-4c15-85a4-49e49158ef7b" xlink:to="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_5759a60b-fd47-4894-8bdc-66c4df71117b" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.icumed.com/role/CondensedConsolidatedStatementsofComprehensiveIncome" xlink:type="simple" xlink:href="icui-20250930.xsd#CondensedConsolidatedStatementsofComprehensiveIncome"/>
  <link:definitionLink xlink:role="http://www.icumed.com/role/CondensedConsolidatedStatementsofComprehensiveIncome" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_b3228222-b7e7-405c-a546-befcf1a73dc6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_5365997e-681d-4d40-962b-709335fd9c85" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_b3228222-b7e7-405c-a546-befcf1a73dc6" xlink:to="loc_us-gaap_StatementTable_5365997e-681d-4d40-962b-709335fd9c85" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementScenarioAxis_a730967c-7fdc-4404-98b0-6ee73e0c6d62" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_StatementScenarioAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_5365997e-681d-4d40-962b-709335fd9c85" xlink:to="loc_srt_StatementScenarioAxis_a730967c-7fdc-4404-98b0-6ee73e0c6d62" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioUnspecifiedDomain_a730967c-7fdc-4404-98b0-6ee73e0c6d62_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ScenarioUnspecifiedDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementScenarioAxis_a730967c-7fdc-4404-98b0-6ee73e0c6d62" xlink:to="loc_srt_ScenarioUnspecifiedDomain_a730967c-7fdc-4404-98b0-6ee73e0c6d62_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioUnspecifiedDomain_1b2e5e5e-8416-4a1d-ae94-d4086143dc93" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ScenarioUnspecifiedDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementScenarioAxis_a730967c-7fdc-4404-98b0-6ee73e0c6d62" xlink:to="loc_srt_ScenarioUnspecifiedDomain_1b2e5e5e-8416-4a1d-ae94-d4086143dc93" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProfitLoss_351f7088-eabc-4fe9-a71f-4677956d216d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ProfitLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_b3228222-b7e7-405c-a546-befcf1a73dc6" xlink:to="loc_us-gaap_ProfitLoss_351f7088-eabc-4fe9-a71f-4677956d216d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPeriodIncreaseDecreaseAbstract_e0b0949f-a435-4fae-97c3-9dd416ae77c5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTaxPeriodIncreaseDecreaseAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_b3228222-b7e7-405c-a546-befcf1a73dc6" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPeriodIncreaseDecreaseAbstract_e0b0949f-a435-4fae-97c3-9dd416ae77c5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossAfterReclassificationAndTax_6e57d2ca-df8f-4212-a9bc-661e008beb50" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossAfterReclassificationAndTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPeriodIncreaseDecreaseAbstract_e0b0949f-a435-4fae-97c3-9dd416ae77c5" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossAfterReclassificationAndTax_6e57d2ca-df8f-4212-a9bc-661e008beb50" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax_89675be5-02cc-4286-89e1-0e5df220ead8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPeriodIncreaseDecreaseAbstract_e0b0949f-a435-4fae-97c3-9dd416ae77c5" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax_89675be5-02cc-4286-89e1-0e5df220ead8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_399c82af-c0b8-4be4-8ad1-ddf9a678076c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPeriodIncreaseDecreaseAbstract_e0b0949f-a435-4fae-97c3-9dd416ae77c5" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_399c82af-c0b8-4be4-8ad1-ddf9a678076c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ComprehensiveIncomeNetOfTax_2741a4e8-0486-4505-b013-50d98dbdaf19" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ComprehensiveIncomeNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_b3228222-b7e7-405c-a546-befcf1a73dc6" xlink:to="loc_us-gaap_ComprehensiveIncomeNetOfTax_2741a4e8-0486-4505-b013-50d98dbdaf19" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.icumed.com/role/CondensedConsolidatedStatementsofStockholdersEquityStatement" xlink:type="simple" xlink:href="icui-20250930.xsd#CondensedConsolidatedStatementsofStockholdersEquityStatement"/>
  <link:definitionLink xlink:role="http://www.icumed.com/role/CondensedConsolidatedStatementsofStockholdersEquityStatement" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_c96520fe-dbdc-4a78-8031-06ccdd736916" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_e3f64499-dbd5-450d-b803-bd9f406648c4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_c96520fe-dbdc-4a78-8031-06ccdd736916" xlink:to="loc_us-gaap_StatementTable_e3f64499-dbd5-450d-b803-bd9f406648c4" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_f847c72e-6b81-45ab-95fb-9149719dc462" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_e3f64499-dbd5-450d-b803-bd9f406648c4" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_f847c72e-6b81-45ab-95fb-9149719dc462" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_f847c72e-6b81-45ab-95fb-9149719dc462_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_f847c72e-6b81-45ab-95fb-9149719dc462" xlink:to="loc_us-gaap_EquityComponentDomain_f847c72e-6b81-45ab-95fb-9149719dc462_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_5389c9cf-2b04-4203-9eea-c7eaaac702c3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_f847c72e-6b81-45ab-95fb-9149719dc462" xlink:to="loc_us-gaap_EquityComponentDomain_5389c9cf-2b04-4203-9eea-c7eaaac702c3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_CommonStockSharesMember_136469ab-a3af-4087-a6c7-5bd21dc0bc64" xlink:href="icui-20250930.xsd#icui_CommonStockSharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_5389c9cf-2b04-4203-9eea-c7eaaac702c3" xlink:to="loc_icui_CommonStockSharesMember_136469ab-a3af-4087-a6c7-5bd21dc0bc64" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_db4ab090-ad58-4e0f-b986-3328ef100d60" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_5389c9cf-2b04-4203-9eea-c7eaaac702c3" xlink:to="loc_us-gaap_CommonStockMember_db4ab090-ad58-4e0f-b986-3328ef100d60" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_777b3f68-45fb-4fc2-98fe-5cfdbb6da953" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AdditionalPaidInCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_5389c9cf-2b04-4203-9eea-c7eaaac702c3" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_777b3f68-45fb-4fc2-98fe-5cfdbb6da953" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockCommonMember_f9bbf009-94ec-4cee-b193-3aacff1bde9d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TreasuryStockCommonMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_5389c9cf-2b04-4203-9eea-c7eaaac702c3" xlink:to="loc_us-gaap_TreasuryStockCommonMember_f9bbf009-94ec-4cee-b193-3aacff1bde9d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_5c128001-c3ad-40f1-ac2a-ba805b10e325" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetainedEarningsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_5389c9cf-2b04-4203-9eea-c7eaaac702c3" xlink:to="loc_us-gaap_RetainedEarningsMember_5c128001-c3ad-40f1-ac2a-ba805b10e325" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_96a7cc49-b7fe-4c1c-a49e-5e80611cc425" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_5389c9cf-2b04-4203-9eea-c7eaaac702c3" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_96a7cc49-b7fe-4c1c-a49e-5e80611cc425" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_4da201e1-3c60-4555-b94c-06d007f6ebfa" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_c96520fe-dbdc-4a78-8031-06ccdd736916" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_4da201e1-3c60-4555-b94c-06d007f6ebfa" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesIssued_f05b8906-812c-44aa-8657-c692f4e07a4e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_4da201e1-3c60-4555-b94c-06d007f6ebfa" xlink:to="loc_us-gaap_CommonStockSharesIssued_f05b8906-812c-44aa-8657-c692f4e07a4e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_ee8c61b2-48d0-4d50-8694-07c0f165f80f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodSharesNewIssues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_4da201e1-3c60-4555-b94c-06d007f6ebfa" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_ee8c61b2-48d0-4d50-8694-07c0f165f80f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesPaidForTaxWithholdingForShareBasedCompensation_734dd727-0f38-45c4-8bc1-eae10a6ce9d5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SharesPaidForTaxWithholdingForShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_4da201e1-3c60-4555-b94c-06d007f6ebfa" xlink:to="loc_us-gaap_SharesPaidForTaxWithholdingForShareBasedCompensation_734dd727-0f38-45c4-8bc1-eae10a6ce9d5" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesIssued_3d0a7748-0598-4ba9-9d05-604b69b782c3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockSharesIssued"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_712a4078-b0f9-4c78-9372-edf0ea631419" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_4da201e1-3c60-4555-b94c-06d007f6ebfa" xlink:to="loc_us-gaap_StockholdersEquity_712a4078-b0f9-4c78-9372-edf0ea631419" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueNewIssues_7546ab8d-9b49-4376-8448-27afb3a2dc47" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodValueNewIssues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_4da201e1-3c60-4555-b94c-06d007f6ebfa" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueNewIssues_7546ab8d-9b49-4376-8448-27afb3a2dc47" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsRelatedToTaxWithholdingForShareBasedCompensation_4e26ce66-2e2c-49ed-8e86-57a01c59d7ac" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AdjustmentsRelatedToTaxWithholdingForShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_4da201e1-3c60-4555-b94c-06d007f6ebfa" xlink:to="loc_us-gaap_AdjustmentsRelatedToTaxWithholdingForShareBasedCompensation_4e26ce66-2e2c-49ed-8e86-57a01c59d7ac" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_384e1b3f-e7c6-490d-90da-be3c1fdf7492" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_4da201e1-3c60-4555-b94c-06d007f6ebfa" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_384e1b3f-e7c6-490d-90da-be3c1fdf7492" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalOther_bf7d6c99-6a5f-45b4-b852-5eb2c9a0f4e6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalOther"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_4da201e1-3c60-4555-b94c-06d007f6ebfa" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalOther_bf7d6c99-6a5f-45b4-b852-5eb2c9a0f4e6" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_3aacc8e5-fadb-42c5-a06b-d234cc9e2690" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_4da201e1-3c60-4555-b94c-06d007f6ebfa" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_3aacc8e5-fadb-42c5-a06b-d234cc9e2690" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationGainLossArisingDuringPeriodNetOfTax_a823d5cd-f4d3-453c-bb98-0960a403c0fd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationGainLossArisingDuringPeriodNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_4da201e1-3c60-4555-b94c-06d007f6ebfa" xlink:to="loc_us-gaap_OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationGainLossArisingDuringPeriodNetOfTax_a823d5cd-f4d3-453c-bb98-0960a403c0fd" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_5522ab3e-9dc8-435c-b411-f4ea65d8cf72" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_4da201e1-3c60-4555-b94c-06d007f6ebfa" xlink:to="loc_us-gaap_NetIncomeLoss_5522ab3e-9dc8-435c-b411-f4ea65d8cf72" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_ba3a8afd-3387-45c4-952d-a96efb2b12de" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockholdersEquity"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.icumed.com/role/CondensedConsolidatedStatementsofCashFlows" xlink:type="simple" xlink:href="icui-20250930.xsd#CondensedConsolidatedStatementsofCashFlows"/>
  <link:definitionLink xlink:role="http://www.icumed.com/role/CondensedConsolidatedStatementsofCashFlows" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_d1d8114e-418a-4f6a-95ee-df0c642f2748" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_50ecacd3-0c23-456d-ac37-4205cb7d9fb1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_d1d8114e-418a-4f6a-95ee-df0c642f2748" xlink:to="loc_us-gaap_StatementTable_50ecacd3-0c23-456d-ac37-4205cb7d9fb1" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementScenarioAxis_3e01c164-2eb1-4b46-8e23-7652ff8a89cc" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_StatementScenarioAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_50ecacd3-0c23-456d-ac37-4205cb7d9fb1" xlink:to="loc_srt_StatementScenarioAxis_3e01c164-2eb1-4b46-8e23-7652ff8a89cc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioUnspecifiedDomain_3e01c164-2eb1-4b46-8e23-7652ff8a89cc_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ScenarioUnspecifiedDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementScenarioAxis_3e01c164-2eb1-4b46-8e23-7652ff8a89cc" xlink:to="loc_srt_ScenarioUnspecifiedDomain_3e01c164-2eb1-4b46-8e23-7652ff8a89cc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioUnspecifiedDomain_1687f532-bcd7-474d-bcf7-07c3624541cb" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ScenarioUnspecifiedDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementScenarioAxis_3e01c164-2eb1-4b46-8e23-7652ff8a89cc" xlink:to="loc_srt_ScenarioUnspecifiedDomain_1687f532-bcd7-474d-bcf7-07c3624541cb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffectAbstract_6e4937d9-0672-4b4a-abfc-e2902b535cd8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffectAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_d1d8114e-418a-4f6a-95ee-df0c642f2748" xlink:to="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffectAbstract_6e4937d9-0672-4b4a-abfc-e2902b535cd8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseExcludingExchangeRateEffectAbstract_f8b17d68-851b-4013-9b57-e71da9a332e3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseExcludingExchangeRateEffectAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffectAbstract_6e4937d9-0672-4b4a-abfc-e2902b535cd8" xlink:to="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseExcludingExchangeRateEffectAbstract_f8b17d68-851b-4013-9b57-e71da9a332e3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_35e4f2fb-6dbb-4f6b-aa26-fc792ef3e709" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseExcludingExchangeRateEffectAbstract_f8b17d68-851b-4013-9b57-e71da9a332e3" xlink:to="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_35e4f2fb-6dbb-4f6b-aa26-fc792ef3e709" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProfitLoss_2a60a6ed-bb5c-4512-a5e0-f7e0510def0b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ProfitLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_35e4f2fb-6dbb-4f6b-aa26-fc792ef3e709" xlink:to="loc_us-gaap_ProfitLoss_2a60a6ed-bb5c-4512-a5e0-f7e0510def0b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DepreciationDepletionAndAmortization_ca944b1a-27a2-45da-a151-62e0f08e9c4d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DepreciationDepletionAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_35e4f2fb-6dbb-4f6b-aa26-fc792ef3e709" xlink:to="loc_us-gaap_DepreciationDepletionAndAmortization_ca944b1a-27a2-45da-a151-62e0f08e9c4d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseRightOfUseAssetAmortizationExpense_c0889b29-4f6b-44f0-b0c3-f03f41794f95" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingLeaseRightOfUseAssetAmortizationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_35e4f2fb-6dbb-4f6b-aa26-fc792ef3e709" xlink:to="loc_us-gaap_OperatingLeaseRightOfUseAssetAmortizationExpense_c0889b29-4f6b-44f0-b0c3-f03f41794f95" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensation_31823789-22c0-4d47-96e5-276167130a57" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_35e4f2fb-6dbb-4f6b-aa26-fc792ef3e709" xlink:to="loc_us-gaap_ShareBasedCompensation_31823789-22c0-4d47-96e5-276167130a57" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainLossOnSaleOfPropertyPlantEquipment_9be98b1d-69c6-41a0-989d-b89351c7e661" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GainLossOnSaleOfPropertyPlantEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_35e4f2fb-6dbb-4f6b-aa26-fc792ef3e709" xlink:to="loc_us-gaap_GainLossOnSaleOfPropertyPlantEquipment_9be98b1d-69c6-41a0-989d-b89351c7e661" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AmortizationOfFinancingCosts_72905191-ba47-4967-bfcd-d1465e4d5177" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AmortizationOfFinancingCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_35e4f2fb-6dbb-4f6b-aa26-fc792ef3e709" xlink:to="loc_us-gaap_AmortizationOfFinancingCosts_72905191-ba47-4967-bfcd-d1465e4d5177" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationContingentConsiderationArrangementsChangeInAmountOfContingentConsiderationLiability1_a6fb3646-7d21-45e6-96de-969a0c450384" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationContingentConsiderationArrangementsChangeInAmountOfContingentConsiderationLiability1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_35e4f2fb-6dbb-4f6b-aa26-fc792ef3e709" xlink:to="loc_us-gaap_BusinessCombinationContingentConsiderationArrangementsChangeInAmountOfContingentConsiderationLiability1_a6fb3646-7d21-45e6-96de-969a0c450384" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromEquityMethodInvestments_7b2eb3c8-10da-4e8f-88c1-53b78740b6b5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeLossFromEquityMethodInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_35e4f2fb-6dbb-4f6b-aa26-fc792ef3e709" xlink:to="loc_us-gaap_IncomeLossFromEquityMethodInvestments_7b2eb3c8-10da-4e8f-88c1-53b78740b6b5" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupNotDiscontinuedOperationGainLossOnDisposal_b2392f32-5204-4ef4-885e-dfec85ad4f97" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupNotDiscontinuedOperationGainLossOnDisposal"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_35e4f2fb-6dbb-4f6b-aa26-fc792ef3e709" xlink:to="loc_us-gaap_DisposalGroupNotDiscontinuedOperationGainLossOnDisposal_b2392f32-5204-4ef4-885e-dfec85ad4f97" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherNoncashIncomeExpense_6d478f1c-b051-42d5-a847-c87d960b7fa5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherNoncashIncomeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_35e4f2fb-6dbb-4f6b-aa26-fc792ef3e709" xlink:to="loc_us-gaap_OtherNoncashIncomeExpense_6d478f1c-b051-42d5-a847-c87d960b7fa5" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInAccountsReceivable_4eb282f8-58c3-4ba7-a32c-fb9fe79041b9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncreaseDecreaseInAccountsReceivable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_35e4f2fb-6dbb-4f6b-aa26-fc792ef3e709" xlink:to="loc_us-gaap_IncreaseDecreaseInAccountsReceivable_4eb282f8-58c3-4ba7-a32c-fb9fe79041b9" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInInventories_4199f4fe-7139-4b5b-8fc5-e3b13d4ecded" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncreaseDecreaseInInventories"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_35e4f2fb-6dbb-4f6b-aa26-fc792ef3e709" xlink:to="loc_us-gaap_IncreaseDecreaseInInventories_4199f4fe-7139-4b5b-8fc5-e3b13d4ecded" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets_aeb207d3-e455-42fa-badc-7b1d59783fe3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_35e4f2fb-6dbb-4f6b-aa26-fc792ef3e709" xlink:to="loc_us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets_aeb207d3-e455-42fa-badc-7b1d59783fe3" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInOtherOperatingAssets_09714ae3-ab50-40e7-b7ab-1e862cda50a4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncreaseDecreaseInOtherOperatingAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_35e4f2fb-6dbb-4f6b-aa26-fc792ef3e709" xlink:to="loc_us-gaap_IncreaseDecreaseInOtherOperatingAssets_09714ae3-ab50-40e7-b7ab-1e862cda50a4" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInAccountsPayable_adbab357-8981-4bce-987e-e57dc789be61" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncreaseDecreaseInAccountsPayable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_35e4f2fb-6dbb-4f6b-aa26-fc792ef3e709" xlink:to="loc_us-gaap_IncreaseDecreaseInAccountsPayable_adbab357-8981-4bce-987e-e57dc789be61" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInAccruedLiabilities_e665251b-8d04-4bfd-85ce-d1c835879717" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncreaseDecreaseInAccruedLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_35e4f2fb-6dbb-4f6b-aa26-fc792ef3e709" xlink:to="loc_us-gaap_IncreaseDecreaseInAccruedLiabilities_e665251b-8d04-4bfd-85ce-d1c835879717" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_IncreaseDecreaseinincometaxesincludingexcesstaxbenefitsanddeferredincometaxes_5d9908ea-1d4d-402c-a506-08b107563cd7" xlink:href="icui-20250930.xsd#icui_IncreaseDecreaseinincometaxesincludingexcesstaxbenefitsanddeferredincometaxes"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_35e4f2fb-6dbb-4f6b-aa26-fc792ef3e709" xlink:to="loc_icui_IncreaseDecreaseinincometaxesincludingexcesstaxbenefitsanddeferredincometaxes_5d9908ea-1d4d-402c-a506-08b107563cd7" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_8fc5907f-c5a8-44c0-8fb8-e3e55232d06b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_35e4f2fb-6dbb-4f6b-aa26-fc792ef3e709" xlink:to="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_8fc5907f-c5a8-44c0-8fb8-e3e55232d06b" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_7def8a83-73c8-4b9d-8d43-5cf663f9f818" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseExcludingExchangeRateEffectAbstract_f8b17d68-851b-4013-9b57-e71da9a332e3" xlink:to="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_7def8a83-73c8-4b9d-8d43-5cf663f9f818" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_0fb991a5-57fe-41a4-9162-32a4b21ac19c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PaymentsToAcquirePropertyPlantAndEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_7def8a83-73c8-4b9d-8d43-5cf663f9f818" xlink:to="loc_us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_0fb991a5-57fe-41a4-9162-32a4b21ac19c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromSalesOfBusinessAffiliateAndProductiveAssets_7abd8022-c436-41c8-b553-b121463d30b6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ProceedsFromSalesOfBusinessAffiliateAndProductiveAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_7def8a83-73c8-4b9d-8d43-5cf663f9f818" xlink:to="loc_us-gaap_ProceedsFromSalesOfBusinessAffiliateAndProductiveAssets_7abd8022-c436-41c8-b553-b121463d30b6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromSaleOfPropertyPlantAndEquipment_1a28c304-4416-4c9a-80f3-45f2d3f32e7e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ProceedsFromSaleOfPropertyPlantAndEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_7def8a83-73c8-4b9d-8d43-5cf663f9f818" xlink:to="loc_us-gaap_ProceedsFromSaleOfPropertyPlantAndEquipment_1a28c304-4416-4c9a-80f3-45f2d3f32e7e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireIntangibleAssets_a9d1d649-b0f2-4929-9047-308531c69854" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PaymentsToAcquireIntangibleAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_7def8a83-73c8-4b9d-8d43-5cf663f9f818" xlink:to="loc_us-gaap_PaymentsToAcquireIntangibleAssets_a9d1d649-b0f2-4929-9047-308531c69854" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromSaleAndMaturityOfMarketableSecurities_5d9ab2f8-b5e3-4cd0-acd3-1eb6770076cf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ProceedsFromSaleAndMaturityOfMarketableSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_7def8a83-73c8-4b9d-8d43-5cf663f9f818" xlink:to="loc_us-gaap_ProceedsFromSaleAndMaturityOfMarketableSecurities_5d9ab2f8-b5e3-4cd0-acd3-1eb6770076cf" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_ae8817fd-68e9-43d5-9f2f-46b1366a01a1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_7def8a83-73c8-4b9d-8d43-5cf663f9f818" xlink:to="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_ae8817fd-68e9-43d5-9f2f-46b1366a01a1" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_fdc7fdb1-2f4a-424f-acb1-9cb58074f3ae" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseExcludingExchangeRateEffectAbstract_f8b17d68-851b-4013-9b57-e71da9a332e3" xlink:to="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_fdc7fdb1-2f4a-424f-acb1-9cb58074f3ae" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RepaymentsOfLongTermDebt_eb045392-3fd6-4867-bc4a-6127107a4f6f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RepaymentsOfLongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_fdc7fdb1-2f4a-424f-acb1-9cb58074f3ae" xlink:to="loc_us-gaap_RepaymentsOfLongTermDebt_eb045392-3fd6-4867-bc4a-6127107a4f6f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromStockOptionsExercised_f74af197-5e05-4e37-ba1f-d813eb41778e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ProceedsFromStockOptionsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_fdc7fdb1-2f4a-424f-acb1-9cb58074f3ae" xlink:to="loc_us-gaap_ProceedsFromStockOptionsExercised_f74af197-5e05-4e37-ba1f-d813eb41778e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinanceLeasePrincipalPayments_da827168-8794-4d7d-a778-ada5659ac259" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinanceLeasePrincipalPayments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_fdc7fdb1-2f4a-424f-acb1-9cb58074f3ae" xlink:to="loc_us-gaap_FinanceLeasePrincipalPayments_da827168-8794-4d7d-a778-ada5659ac259" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentForContingentConsiderationLiabilityFinancingActivities_bbe1faa0-0b16-4e12-8b5d-bc54117e97c9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PaymentForContingentConsiderationLiabilityFinancingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_fdc7fdb1-2f4a-424f-acb1-9cb58074f3ae" xlink:to="loc_us-gaap_PaymentForContingentConsiderationLiabilityFinancingActivities_bbe1faa0-0b16-4e12-8b5d-bc54117e97c9" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsRelatedToTaxWithholdingForShareBasedCompensation_e78d4027-7d45-4f64-888e-39155f7e9ab7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PaymentsRelatedToTaxWithholdingForShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_fdc7fdb1-2f4a-424f-acb1-9cb58074f3ae" xlink:to="loc_us-gaap_PaymentsRelatedToTaxWithholdingForShareBasedCompensation_e78d4027-7d45-4f64-888e-39155f7e9ab7" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_6bd0b179-eec2-455c-9d31-000efc4f3e1a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_fdc7fdb1-2f4a-424f-acb1-9cb58074f3ae" xlink:to="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_6bd0b179-eec2-455c-9d31-000efc4f3e1a" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectOfExchangeRateOnCashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsIncludingDisposalGroupAndDiscontinuedOperationsAbstract_acf9a185-c758-43a3-b30c-c3fd8128dbf6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EffectOfExchangeRateOnCashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsIncludingDisposalGroupAndDiscontinuedOperationsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffectAbstract_6e4937d9-0672-4b4a-abfc-e2902b535cd8" xlink:to="loc_us-gaap_EffectOfExchangeRateOnCashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsIncludingDisposalGroupAndDiscontinuedOperationsAbstract_acf9a185-c758-43a3-b30c-c3fd8128dbf6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectOfExchangeRateOnCashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_22d9e1e8-a43a-43ff-8b28-073b913f79cf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EffectOfExchangeRateOnCashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EffectOfExchangeRateOnCashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsIncludingDisposalGroupAndDiscontinuedOperationsAbstract_acf9a185-c758-43a3-b30c-c3fd8128dbf6" xlink:to="loc_us-gaap_EffectOfExchangeRateOnCashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_22d9e1e8-a43a-43ff-8b28-073b913f79cf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect_650c9952-b3d8-4110-abdc-d65c840217b2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_d1d8114e-418a-4f6a-95ee-df0c642f2748" xlink:to="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect_650c9952-b3d8-4110-abdc-d65c840217b2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_d5fa664c-b767-46ce-bb97-8de807b5a056" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_d1d8114e-418a-4f6a-95ee-df0c642f2748" xlink:to="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_d5fa664c-b767-46ce-bb97-8de807b5a056" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SupplementalCashFlowInformationAbstract_11a96d87-87df-482d-b865-9ddd7c902519" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SupplementalCashFlowInformationAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_d1d8114e-418a-4f6a-95ee-df0c642f2748" xlink:to="loc_us-gaap_SupplementalCashFlowInformationAbstract_11a96d87-87df-482d-b865-9ddd7c902519" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalExpendituresIncurredButNotYetPaid_b4ac3d68-b579-41ab-a9f1-0e352cfec809" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CapitalExpendituresIncurredButNotYetPaid"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SupplementalCashFlowInformationAbstract_11a96d87-87df-482d-b865-9ddd7c902519" xlink:to="loc_us-gaap_CapitalExpendituresIncurredButNotYetPaid_b4ac3d68-b579-41ab-a9f1-0e352cfec809" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NoncashInvestingAndFinancingItemsAbstract_df1c5e65-850f-4549-b9f7-9b323614af08" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NoncashInvestingAndFinancingItemsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_d1d8114e-418a-4f6a-95ee-df0c642f2748" xlink:to="loc_us-gaap_NoncashInvestingAndFinancingItemsAbstract_df1c5e65-850f-4549-b9f7-9b323614af08" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransferToInvestments_5eec9815-606a-4d56-be12-32e1ba3f8b27" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TransferToInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NoncashInvestingAndFinancingItemsAbstract_df1c5e65-850f-4549-b9f7-9b323614af08" xlink:to="loc_us-gaap_TransferToInvestments_5eec9815-606a-4d56-be12-32e1ba3f8b27" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.icumed.com/role/RestructuringStrategicTransactionandIntegrationLiabilityDetails" xlink:type="simple" xlink:href="icui-20250930.xsd#RestructuringStrategicTransactionandIntegrationLiabilityDetails"/>
  <link:definitionLink xlink:role="http://www.icumed.com/role/RestructuringStrategicTransactionandIntegrationLiabilityDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCostAndReserveLineItems_5f091759-35c1-422a-abfc-d43df8e0ceee" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringCostAndReserveLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_509df46e-3d65-4a43-96aa-a24733fe0943" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfRestructuringAndRelatedCostsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_5f091759-35c1-422a-abfc-d43df8e0ceee" xlink:to="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_509df46e-3d65-4a43-96aa-a24733fe0943" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCostAndReserveAxis_3ca46484-895d-427a-a4e3-9b1e31584d13" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringCostAndReserveAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_509df46e-3d65-4a43-96aa-a24733fe0943" xlink:to="loc_us-gaap_RestructuringCostAndReserveAxis_3ca46484-895d-427a-a4e3-9b1e31584d13" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfRestructuringDomain_3ca46484-895d-427a-a4e3-9b1e31584d13_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TypeOfRestructuringDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RestructuringCostAndReserveAxis_3ca46484-895d-427a-a4e3-9b1e31584d13" xlink:to="loc_us-gaap_TypeOfRestructuringDomain_3ca46484-895d-427a-a4e3-9b1e31584d13_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfRestructuringDomain_bbc4a071-2cd3-44c8-8cbc-9bc44ae81994" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TypeOfRestructuringDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RestructuringCostAndReserveAxis_3ca46484-895d-427a-a4e3-9b1e31584d13" xlink:to="loc_us-gaap_TypeOfRestructuringDomain_bbc4a071-2cd3-44c8-8cbc-9bc44ae81994" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeSeveranceMember_a624594f-c8e1-432b-aa3e-61cdb27f4535" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeSeveranceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TypeOfRestructuringDomain_bbc4a071-2cd3-44c8-8cbc-9bc44ae81994" xlink:to="loc_us-gaap_EmployeeSeveranceMember_a624594f-c8e1-432b-aa3e-61cdb27f4535" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FacilityClosingMember_55cad160-e0b6-4973-a47b-0998ffac0a87" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FacilityClosingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TypeOfRestructuringDomain_bbc4a071-2cd3-44c8-8cbc-9bc44ae81994" xlink:to="loc_us-gaap_FacilityClosingMember_55cad160-e0b6-4973-a47b-0998ffac0a87" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringReserve_22f798b1-b518-4fd8-9911-6d57774fbd3f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringReserve"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_5f091759-35c1-422a-abfc-d43df8e0ceee" xlink:to="loc_us-gaap_RestructuringReserve_22f798b1-b518-4fd8-9911-6d57774fbd3f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCharges_ca2633b9-d14e-409c-915d-c94071a1383a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringCharges"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_5f091759-35c1-422a-abfc-d43df8e0ceee" xlink:to="loc_us-gaap_RestructuringCharges_ca2633b9-d14e-409c-915d-c94071a1383a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsForRestructuring_2003d516-700b-4589-9a1b-74ad9f48d0d9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PaymentsForRestructuring"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_5f091759-35c1-422a-abfc-d43df8e0ceee" xlink:to="loc_us-gaap_PaymentsForRestructuring_2003d516-700b-4589-9a1b-74ad9f48d0d9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringReserveAccrualAdjustment1_455d4ae2-0259-4732-ac9c-0de16f880c96" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringReserveAccrualAdjustment1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_5f091759-35c1-422a-abfc-d43df8e0ceee" xlink:to="loc_us-gaap_RestructuringReserveAccrualAdjustment1_455d4ae2-0259-4732-ac9c-0de16f880c96" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringReserveTranslationAdjustment_2d6b3741-bf77-4319-a903-973952991a8a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringReserveTranslationAdjustment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_5f091759-35c1-422a-abfc-d43df8e0ceee" xlink:to="loc_us-gaap_RestructuringReserveTranslationAdjustment_2d6b3741-bf77-4319-a903-973952991a8a" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringReserve_53c16838-fc5d-4bf6-9097-7389fb8c1fde" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringReserve"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.icumed.com/role/DiscontinuedOperationsandDisposalGroupsTextDetails" xlink:type="simple" xlink:href="icui-20250930.xsd#DiscontinuedOperationsandDisposalGroupsTextDetails"/>
  <link:definitionLink xlink:role="http://www.icumed.com/role/DiscontinuedOperationsandDisposalGroupsTextDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_a79cc9ee-5749-4721-99c8-7125fcd667ef" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_24e759b2-53a3-4ee5-a4f5-27a3515ade05" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_a79cc9ee-5749-4721-99c8-7125fcd667ef" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_24e759b2-53a3-4ee5-a4f5-27a3515ade05" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_79edf835-1c45-47a9-b116-85f717e63f96" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_24e759b2-53a3-4ee5-a4f5-27a3515ade05" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_79edf835-1c45-47a9-b116-85f717e63f96" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_79edf835-1c45-47a9-b116-85f717e63f96_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_79edf835-1c45-47a9-b116-85f717e63f96" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_79edf835-1c45-47a9-b116-85f717e63f96_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_eb19a228-b63b-4acc-9cda-79e2702ca3b9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_79edf835-1c45-47a9-b116-85f717e63f96" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_eb19a228-b63b-4acc-9cda-79e2702ca3b9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_IVSolutionsMember_6f7834ff-0d02-47b6-b467-cd9ddfc60015" xlink:href="icui-20250930.xsd#icui_IVSolutionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_eb19a228-b63b-4acc-9cda-79e2702ca3b9" xlink:to="loc_icui_IVSolutionsMember_6f7834ff-0d02-47b6-b467-cd9ddfc60015" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationAxis_79114639-d907-4733-92be-cb087c1ac71e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupClassificationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_24e759b2-53a3-4ee5-a4f5-27a3515ade05" xlink:to="loc_us-gaap_DisposalGroupClassificationAxis_79114639-d907-4733-92be-cb087c1ac71e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_79114639-d907-4733-92be-cb087c1ac71e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_79114639-d907-4733-92be-cb087c1ac71e" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_79114639-d907-4733-92be-cb087c1ac71e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_248dd542-078e-4db6-880f-30aa1a13b5c2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_79114639-d907-4733-92be-cb087c1ac71e" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_248dd542-078e-4db6-880f-30aa1a13b5c2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupHeldforsaleNotDiscontinuedOperationsMember_81967aed-f28e-476a-9c5a-d7b0ecc8a611" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupHeldforsaleNotDiscontinuedOperationsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupClassificationDomain_248dd542-078e-4db6-880f-30aa1a13b5c2" xlink:to="loc_us-gaap_DisposalGroupHeldforsaleNotDiscontinuedOperationsMember_81967aed-f28e-476a-9c5a-d7b0ecc8a611" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationAccountsNotesAndLoansReceivableNet_d9a8c890-86eb-4068-9ae0-286165deff2f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupIncludingDiscontinuedOperationAccountsNotesAndLoansReceivableNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_a79cc9ee-5749-4721-99c8-7125fcd667ef" xlink:to="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationAccountsNotesAndLoansReceivableNet_d9a8c890-86eb-4068-9ae0-286165deff2f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationInventory1_1400ab2b-a88b-46df-8339-b670381cef61" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupIncludingDiscontinuedOperationInventory1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_a79cc9ee-5749-4721-99c8-7125fcd667ef" xlink:to="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationInventory1_1400ab2b-a88b-46df-8339-b670381cef61" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationPrepaidAndOtherAssets_0e3ec54e-2578-4852-889b-9168d7884f58" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupIncludingDiscontinuedOperationPrepaidAndOtherAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_a79cc9ee-5749-4721-99c8-7125fcd667ef" xlink:to="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationPrepaidAndOtherAssets_0e3ec54e-2578-4852-889b-9168d7884f58" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationPropertyPlantAndEquipment_2163bef8-ed7b-4c0b-905f-b0270aa83fd8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupIncludingDiscontinuedOperationPropertyPlantAndEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_a79cc9ee-5749-4721-99c8-7125fcd667ef" xlink:to="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationPropertyPlantAndEquipment_2163bef8-ed7b-4c0b-905f-b0270aa83fd8" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationOtherAssets_082ff559-7e65-4ac8-9759-901c13913577" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupIncludingDiscontinuedOperationOtherAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_a79cc9ee-5749-4721-99c8-7125fcd667ef" xlink:to="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationOtherAssets_082ff559-7e65-4ac8-9759-901c13913577" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsOfDisposalGroupIncludingDiscontinuedOperation_18a0255e-eeb8-4f58-919a-3615b52f8972" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AssetsOfDisposalGroupIncludingDiscontinuedOperation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_a79cc9ee-5749-4721-99c8-7125fcd667ef" xlink:to="loc_us-gaap_AssetsOfDisposalGroupIncludingDiscontinuedOperation_18a0255e-eeb8-4f58-919a-3615b52f8972" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationAccountsPayable_544c7c45-88b0-436e-a40c-5abfdc1a6a54" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupIncludingDiscontinuedOperationAccountsPayable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_a79cc9ee-5749-4721-99c8-7125fcd667ef" xlink:to="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationAccountsPayable_544c7c45-88b0-436e-a40c-5abfdc1a6a54" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationAccruedLiabilities_b869568e-0379-4aca-ae4a-8a9b5dde920e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupIncludingDiscontinuedOperationAccruedLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_a79cc9ee-5749-4721-99c8-7125fcd667ef" xlink:to="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationAccruedLiabilities_b869568e-0379-4aca-ae4a-8a9b5dde920e" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesOfDisposalGroupIncludingDiscontinuedOperation_2293ad36-85ed-4ce3-9a00-828277753a8f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LiabilitiesOfDisposalGroupIncludingDiscontinuedOperation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_a79cc9ee-5749-4721-99c8-7125fcd667ef" xlink:to="loc_us-gaap_LiabilitiesOfDisposalGroupIncludingDiscontinuedOperation_2293ad36-85ed-4ce3-9a00-828277753a8f" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_DisposalGroupNetAssetsHeldForSale_f64f7a08-4e37-452d-8efa-30fd8ea3ab0e" xlink:href="icui-20250930.xsd#icui_DisposalGroupNetAssetsHeldForSale"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_a79cc9ee-5749-4721-99c8-7125fcd667ef" xlink:to="loc_icui_DisposalGroupNetAssetsHeldForSale_f64f7a08-4e37-452d-8efa-30fd8ea3ab0e" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_DisposalGroupAccountsReceivableAllowanceForCreditLosses_613f914c-e57f-4f44-8c05-dce41148d2a4" xlink:href="icui-20250930.xsd#icui_DisposalGroupAccountsReceivableAllowanceForCreditLosses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_a79cc9ee-5749-4721-99c8-7125fcd667ef" xlink:to="loc_icui_DisposalGroupAccountsReceivableAllowanceForCreditLosses_613f914c-e57f-4f44-8c05-dce41148d2a4" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromSalesOfBusinessAffiliateAndProductiveAssets_df12211c-329e-4a98-abb4-65cce9917a18" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ProceedsFromSalesOfBusinessAffiliateAndProductiveAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_a79cc9ee-5749-4721-99c8-7125fcd667ef" xlink:to="loc_us-gaap_ProceedsFromSalesOfBusinessAffiliateAndProductiveAssets_df12211c-329e-4a98-abb4-65cce9917a18" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupNotDiscontinuedOperationGainLossOnDisposal_950d17b5-209e-414c-85e1-f1a11767ee56" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupNotDiscontinuedOperationGainLossOnDisposal"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_a79cc9ee-5749-4721-99c8-7125fcd667ef" xlink:to="loc_us-gaap_DisposalGroupNotDiscontinuedOperationGainLossOnDisposal_950d17b5-209e-414c-85e1-f1a11767ee56" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_GainOnSaleOfNoncontrollingInterestInDisposalGroupBeforeFMVOfRetainedInterest_2731b224-8a2c-4f51-8695-95f290163cae" xlink:href="icui-20250930.xsd#icui_GainOnSaleOfNoncontrollingInterestInDisposalGroupBeforeFMVOfRetainedInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_a79cc9ee-5749-4721-99c8-7125fcd667ef" xlink:to="loc_icui_GainOnSaleOfNoncontrollingInterestInDisposalGroupBeforeFMVOfRetainedInterest_2731b224-8a2c-4f51-8695-95f290163cae" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedInterestFairValueDisclosure_3d234f2e-31b9-45c1-8ef6-caed2d4aee9f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetainedInterestFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_a79cc9ee-5749-4721-99c8-7125fcd667ef" xlink:to="loc_us-gaap_RetainedInterestFairValueDisclosure_3d234f2e-31b9-45c1-8ef6-caed2d4aee9f" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossOnContracts_9c1c2819-b2a8-4325-8b62-c292eab39b73" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LossOnContracts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_a79cc9ee-5749-4721-99c8-7125fcd667ef" xlink:to="loc_us-gaap_LossOnContracts_9c1c2819-b2a8-4325-8b62-c292eab39b73" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_UsGaap_TSAFees_8b283bbb-c361-4cbe-8979-b9f73a37ee4b" xlink:href="icui-20250930.xsd#icui_UsGaap_TSAFees"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_a79cc9ee-5749-4721-99c8-7125fcd667ef" xlink:to="loc_icui_UsGaap_TSAFees_8b283bbb-c361-4cbe-8979-b9f73a37ee4b" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_UsGaap_ReleaseofProvisionForLossOnContracts_46f38953-1fa2-48c4-978a-2c36b371e4a6" xlink:href="icui-20250930.xsd#icui_UsGaap_ReleaseofProvisionForLossOnContracts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_a79cc9ee-5749-4721-99c8-7125fcd667ef" xlink:to="loc_icui_UsGaap_ReleaseofProvisionForLossOnContracts_46f38953-1fa2-48c4-978a-2c36b371e4a6" xlink:type="arc" order="17"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.icumed.com/role/DiscontinuedOperationsandDisposalGroupsRelatedPartyDetails" xlink:type="simple" xlink:href="icui-20250930.xsd#DiscontinuedOperationsandDisposalGroupsRelatedPartyDetails"/>
  <link:definitionLink xlink:role="http://www.icumed.com/role/DiscontinuedOperationsandDisposalGroupsRelatedPartyDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionLineItems_a94ce9bd-29b1-456e-8a63-8538a2d10885" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyTransactionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_ff6a32c7-2640-4047-b997-fc516ed99437" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_a94ce9bd-29b1-456e-8a63-8538a2d10885" xlink:to="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_ff6a32c7-2640-4047-b997-fc516ed99437" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_b491cbc5-4e59-4984-86d1-fbb178bffe7e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_ff6a32c7-2640-4047-b997-fc516ed99437" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_b491cbc5-4e59-4984-86d1-fbb178bffe7e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_b491cbc5-4e59-4984-86d1-fbb178bffe7e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_b491cbc5-4e59-4984-86d1-fbb178bffe7e" xlink:to="loc_us-gaap_RelatedPartyDomain_b491cbc5-4e59-4984-86d1-fbb178bffe7e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_524d5b25-b03e-4d93-99d8-3ce5673d051a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_b491cbc5-4e59-4984-86d1-fbb178bffe7e" xlink:to="loc_us-gaap_RelatedPartyDomain_524d5b25-b03e-4d93-99d8-3ce5673d051a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityMethodInvesteeMember_905b92a0-95b0-4871-8778-a703e88974d3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityMethodInvesteeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_524d5b25-b03e-4d93-99d8-3ce5673d051a" xlink:to="loc_us-gaap_EquityMethodInvesteeMember_905b92a0-95b0-4871-8778-a703e88974d3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationAxis_0e96c282-49e2-4d45-af0f-444034a18f6b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_ff6a32c7-2640-4047-b997-fc516ed99437" xlink:to="loc_us-gaap_IncomeStatementLocationAxis_0e96c282-49e2-4d45-af0f-444034a18f6b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_0e96c282-49e2-4d45-af0f-444034a18f6b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_0e96c282-49e2-4d45-af0f-444034a18f6b" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_0e96c282-49e2-4d45-af0f-444034a18f6b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_fc742ab8-f4f3-4f1e-a8e2-eb947736949e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_0e96c282-49e2-4d45-af0f-444034a18f6b" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_fc742ab8-f4f3-4f1e-a8e2-eb947736949e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfSalesMember_48b53f63-b78c-4382-a246-9f205e4ea990" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CostOfSalesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_fc742ab8-f4f3-4f1e-a8e2-eb947736949e" xlink:to="loc_us-gaap_CostOfSalesMember_48b53f63-b78c-4382-a246-9f205e4ea990" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SellingGeneralAndAdministrativeExpensesMember_f20bf62c-9daa-469e-bcee-7fe6ec49eae8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SellingGeneralAndAdministrativeExpensesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_fc742ab8-f4f3-4f1e-a8e2-eb947736949e" xlink:to="loc_us-gaap_SellingGeneralAndAdministrativeExpensesMember_f20bf62c-9daa-469e-bcee-7fe6ec49eae8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_ManufacturingServicesAgreementRevenue_83fae94c-7df9-4299-b281-84f9869acb7c" xlink:href="icui-20250930.xsd#icui_ManufacturingServicesAgreementRevenue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_a94ce9bd-29b1-456e-8a63-8538a2d10885" xlink:to="loc_icui_ManufacturingServicesAgreementRevenue_83fae94c-7df9-4299-b281-84f9869acb7c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartiesAmountInCostOfSales_ee97d973-1222-4975-807c-5d9bcb74a7c1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartiesAmountInCostOfSales"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_a94ce9bd-29b1-456e-8a63-8538a2d10885" xlink:to="loc_us-gaap_RelatedPartiesAmountInCostOfSales_ee97d973-1222-4975-807c-5d9bcb74a7c1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_ServiceFeesOtsukaICUMedicalLLC_e6b1635a-48af-4fab-a05d-a7e384f1a464" xlink:href="icui-20250930.xsd#icui_ServiceFeesOtsukaICUMedicalLLC"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_a94ce9bd-29b1-456e-8a63-8538a2d10885" xlink:to="loc_icui_ServiceFeesOtsukaICUMedicalLLC_e6b1635a-48af-4fab-a05d-a7e384f1a464" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_RelatedPartyEquityInEarningsOfUnconsolidatedAffiliates_23a2d795-4a88-4f23-bb17-943f658ec8c0" xlink:href="icui-20250930.xsd#icui_RelatedPartyEquityInEarningsOfUnconsolidatedAffiliates"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_a94ce9bd-29b1-456e-8a63-8538a2d10885" xlink:to="loc_icui_RelatedPartyEquityInEarningsOfUnconsolidatedAffiliates_23a2d795-4a88-4f23-bb17-943f658ec8c0" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_RelatedPartyPayable_2dd51b2f-f3cb-403f-a299-c3bcc3c5ac92" xlink:href="icui-20250930.xsd#icui_RelatedPartyPayable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_a94ce9bd-29b1-456e-8a63-8538a2d10885" xlink:to="loc_icui_RelatedPartyPayable_2dd51b2f-f3cb-403f-a299-c3bcc3c5ac92" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.icumed.com/role/RevenueDisaggregatedRevenuebyProductLineDetails" xlink:type="simple" xlink:href="icui-20250930.xsd#RevenueDisaggregatedRevenuebyProductLineDetails"/>
  <link:definitionLink xlink:role="http://www.icumed.com/role/RevenueDisaggregatedRevenuebyProductLineDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_57be5b78-9aa3-4c1f-b76c-1f15e6be081b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisaggregationOfRevenueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueTable_80028acd-0ff5-4675-8651-64e47fa70743" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisaggregationOfRevenueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_57be5b78-9aa3-4c1f-b76c-1f15e6be081b" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_80028acd-0ff5-4675-8651-64e47fa70743" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_5a5fc549-9dc3-4d29-a38d-c9f9a18da551" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_80028acd-0ff5-4675-8651-64e47fa70743" xlink:to="loc_srt_ProductOrServiceAxis_5a5fc549-9dc3-4d29-a38d-c9f9a18da551" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_5a5fc549-9dc3-4d29-a38d-c9f9a18da551_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_5a5fc549-9dc3-4d29-a38d-c9f9a18da551" xlink:to="loc_srt_ProductsAndServicesDomain_5a5fc549-9dc3-4d29-a38d-c9f9a18da551_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_f707013a-e3d6-43ec-b5a0-5562e16b52ba" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_5a5fc549-9dc3-4d29-a38d-c9f9a18da551" xlink:to="loc_srt_ProductsAndServicesDomain_f707013a-e3d6-43ec-b5a0-5562e16b52ba" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_InfusionConsumablesMember_b686fa8c-70eb-4521-8a39-25e7c55c30be" xlink:href="icui-20250930.xsd#icui_InfusionConsumablesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_f707013a-e3d6-43ec-b5a0-5562e16b52ba" xlink:to="loc_icui_InfusionConsumablesMember_b686fa8c-70eb-4521-8a39-25e7c55c30be" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_InfusionSystemsMember_aee79026-9fcf-4bcc-b13c-ae662bf7d0a5" xlink:href="icui-20250930.xsd#icui_InfusionSystemsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_f707013a-e3d6-43ec-b5a0-5562e16b52ba" xlink:to="loc_icui_InfusionSystemsMember_aee79026-9fcf-4bcc-b13c-ae662bf7d0a5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_VitalCareMember_1e0e144b-548d-4620-bb82-bf326f6996b6" xlink:href="icui-20250930.xsd#icui_VitalCareMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_f707013a-e3d6-43ec-b5a0-5562e16b52ba" xlink:to="loc_icui_VitalCareMember_1e0e144b-548d-4620-bb82-bf326f6996b6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Revenues_0ea62a79-d5a4-4eb2-947d-ad6e0a8246d5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_Revenues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_57be5b78-9aa3-4c1f-b76c-1f15e6be081b" xlink:to="loc_us-gaap_Revenues_0ea62a79-d5a4-4eb2-947d-ad6e0a8246d5" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.icumed.com/role/RevenueDisaggregatedRevenuebyGeographyDetails" xlink:type="simple" xlink:href="icui-20250930.xsd#RevenueDisaggregatedRevenuebyGeographyDetails"/>
  <link:definitionLink xlink:role="http://www.icumed.com/role/RevenueDisaggregatedRevenuebyGeographyDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_fc900873-a650-4ee0-b744-ac6319f2426d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisaggregationOfRevenueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueTable_93a33373-716b-45b5-89f4-7bba00ddce50" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisaggregationOfRevenueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_fc900873-a650-4ee0-b744-ac6319f2426d" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_93a33373-716b-45b5-89f4-7bba00ddce50" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementGeographicalAxis_54c625ec-28f4-4bc6-938b-b863010bcff4" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_StatementGeographicalAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_93a33373-716b-45b5-89f4-7bba00ddce50" xlink:to="loc_srt_StatementGeographicalAxis_54c625ec-28f4-4bc6-938b-b863010bcff4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_54c625ec-28f4-4bc6-938b-b863010bcff4_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementGeographicalAxis_54c625ec-28f4-4bc6-938b-b863010bcff4" xlink:to="loc_srt_SegmentGeographicalDomain_54c625ec-28f4-4bc6-938b-b863010bcff4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_fe0d2fdd-2391-47e9-aee7-c477068fe536" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementGeographicalAxis_54c625ec-28f4-4bc6-938b-b863010bcff4" xlink:to="loc_srt_SegmentGeographicalDomain_fe0d2fdd-2391-47e9-aee7-c477068fe536" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_US_46e7e75c-4957-4062-af55-dca693a2a0c5" xlink:href="https://xbrl.sec.gov/country/2025/country-2025.xsd#country_US"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_fe0d2fdd-2391-47e9-aee7-c477068fe536" xlink:to="loc_country_US_46e7e75c-4957-4062-af55-dca693a2a0c5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EMEAMember_b7bd4a59-8a0d-4bd4-9728-48f490a37ae6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EMEAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_fe0d2fdd-2391-47e9-aee7-c477068fe536" xlink:to="loc_us-gaap_EMEAMember_b7bd4a59-8a0d-4bd4-9728-48f490a37ae6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_AsiaPacificMember_d568b0aa-a8fd-4fe5-b37a-a1f25d58efb7" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_AsiaPacificMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_fe0d2fdd-2391-47e9-aee7-c477068fe536" xlink:to="loc_srt_AsiaPacificMember_d568b0aa-a8fd-4fe5-b37a-a1f25d58efb7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_OtherforeigncountriesMember_f81cd27a-0ef0-473e-b64a-d6c9bdc6947f" xlink:href="icui-20250930.xsd#icui_OtherforeigncountriesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_fe0d2fdd-2391-47e9-aee7-c477068fe536" xlink:to="loc_icui_OtherforeigncountriesMember_f81cd27a-0ef0-473e-b64a-d6c9bdc6947f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Revenues_6682f882-4eb9-4dba-9cfb-3e960855b2b1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_Revenues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_fc900873-a650-4ee0-b744-ac6319f2426d" xlink:to="loc_us-gaap_Revenues_6682f882-4eb9-4dba-9cfb-3e960855b2b1" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.icumed.com/role/RevenueContractLiabilitiesDetails" xlink:type="simple" xlink:href="icui-20250930.xsd#RevenueContractLiabilitiesDetails"/>
  <link:definitionLink xlink:role="http://www.icumed.com/role/RevenueContractLiabilitiesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_icui_ContractassetandliabilitybalancesLineItems_c0619310-93c2-474e-83cc-03e4845a4f99" xlink:href="icui-20250930.xsd#icui_ContractassetandliabilitybalancesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_ContractassetandliabilitybalancesTable_d3df2d1f-5ced-42e3-a862-7efa84febbea" xlink:href="icui-20250930.xsd#icui_ContractassetandliabilitybalancesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_icui_ContractassetandliabilitybalancesLineItems_c0619310-93c2-474e-83cc-03e4845a4f99" xlink:to="loc_icui_ContractassetandliabilitybalancesTable_d3df2d1f-5ced-42e3-a862-7efa84febbea" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_79c9d6a8-45de-4564-b041-17fcfda92cc1" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_icui_ContractassetandliabilitybalancesTable_d3df2d1f-5ced-42e3-a862-7efa84febbea" xlink:to="loc_srt_ProductOrServiceAxis_79c9d6a8-45de-4564-b041-17fcfda92cc1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_79c9d6a8-45de-4564-b041-17fcfda92cc1_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_79c9d6a8-45de-4564-b041-17fcfda92cc1" xlink:to="loc_srt_ProductsAndServicesDomain_79c9d6a8-45de-4564-b041-17fcfda92cc1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_ed11fdf5-5375-42ed-9841-8ba32734a809" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_79c9d6a8-45de-4564-b041-17fcfda92cc1" xlink:to="loc_srt_ProductsAndServicesDomain_ed11fdf5-5375-42ed-9841-8ba32734a809" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_EquipmentrevenueMember_8fc23f12-ab27-4d9a-a272-c5b9503a45ac" xlink:href="icui-20250930.xsd#icui_EquipmentrevenueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_ed11fdf5-5375-42ed-9841-8ba32734a809" xlink:to="loc_icui_EquipmentrevenueMember_8fc23f12-ab27-4d9a-a272-c5b9503a45ac" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_SoftwarerevenueMember_ca86e498-bbaa-45d0-b501-0cfdfe22a371" xlink:href="icui-20250930.xsd#icui_SoftwarerevenueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_ed11fdf5-5375-42ed-9841-8ba32734a809" xlink:to="loc_icui_SoftwarerevenueMember_ca86e498-bbaa-45d0-b501-0cfdfe22a371" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_GovernmentGrantRevenueMember_54391203-c73c-4621-b012-a58a5c2ca593" xlink:href="icui-20250930.xsd#icui_GovernmentGrantRevenueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_ed11fdf5-5375-42ed-9841-8ba32734a809" xlink:to="loc_icui_GovernmentGrantRevenueMember_54391203-c73c-4621-b012-a58a5c2ca593" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_OtherDeferredRevenueMember_34acf29a-0feb-4662-929b-47de7b3429ad" xlink:href="icui-20250930.xsd#icui_OtherDeferredRevenueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_ed11fdf5-5375-42ed-9841-8ba32734a809" xlink:to="loc_icui_OtherDeferredRevenueMember_34acf29a-0feb-4662-929b-47de7b3429ad" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MovementInDeferredRevenueRollForward_f4d07970-2254-4eff-8128-403fe7938f90" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MovementInDeferredRevenueRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_icui_ContractassetandliabilitybalancesLineItems_c0619310-93c2-474e-83cc-03e4845a4f99" xlink:to="loc_us-gaap_MovementInDeferredRevenueRollForward_f4d07970-2254-4eff-8128-403fe7938f90" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiability_c5d6fce4-c009-4791-83c5-a8596cfe2b9f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ContractWithCustomerLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_icui_ContractassetandliabilitybalancesLineItems_c0619310-93c2-474e-83cc-03e4845a4f99" xlink:to="loc_us-gaap_ContractWithCustomerLiability_c5d6fce4-c009-4791-83c5-a8596cfe2b9f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInDeferredRevenue_20d645d6-beb9-4038-82a4-eb86c88de0d6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncreaseDecreaseInDeferredRevenue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_icui_ContractassetandliabilitybalancesLineItems_c0619310-93c2-474e-83cc-03e4845a4f99" xlink:to="loc_us-gaap_IncreaseDecreaseInDeferredRevenue_20d645d6-beb9-4038-82a4-eb86c88de0d6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredRevenueAdditions_ae0817cc-9e47-4b31-bc57-4561b08faa08" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DeferredRevenueAdditions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_icui_ContractassetandliabilitybalancesLineItems_c0619310-93c2-474e-83cc-03e4845a4f99" xlink:to="loc_us-gaap_DeferredRevenueAdditions_ae0817cc-9e47-4b31-bc57-4561b08faa08" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiability_9f9ff4f7-11ef-4878-a1ae-cd03def31da3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ContractWithCustomerLiability"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.icumed.com/role/RevenueDeferredRevenuebyArrangementDetails" xlink:type="simple" xlink:href="icui-20250930.xsd#RevenueDeferredRevenuebyArrangementDetails"/>
  <link:definitionLink xlink:role="http://www.icumed.com/role/RevenueDeferredRevenuebyArrangementDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_cba7c696-85fe-4cb7-9609-4d425d6645e3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_4d199ced-b786-43f6-b026-58ca1fd6dc67" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_cba7c696-85fe-4cb7-9609-4d425d6645e3" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_4d199ced-b786-43f6-b026-58ca1fd6dc67" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_TimingAxis_7ad716aa-e9e8-4b08-a2af-9451de1114bf" xlink:href="icui-20250930.xsd#icui_TimingAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_4d199ced-b786-43f6-b026-58ca1fd6dc67" xlink:to="loc_icui_TimingAxis_7ad716aa-e9e8-4b08-a2af-9451de1114bf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_TimingDomain_7ad716aa-e9e8-4b08-a2af-9451de1114bf_default" xlink:href="icui-20250930.xsd#icui_TimingDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_icui_TimingAxis_7ad716aa-e9e8-4b08-a2af-9451de1114bf" xlink:to="loc_icui_TimingDomain_7ad716aa-e9e8-4b08-a2af-9451de1114bf_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_TimingDomain_0b982980-b0d5-4c5b-944c-e070a0936b00" xlink:href="icui-20250930.xsd#icui_TimingDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_icui_TimingAxis_7ad716aa-e9e8-4b08-a2af-9451de1114bf" xlink:to="loc_icui_TimingDomain_0b982980-b0d5-4c5b-944c-e070a0936b00" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_ShortTermMember_8c04fd25-952b-4d73-a848-2d7636061236" xlink:href="icui-20250930.xsd#icui_ShortTermMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_icui_TimingDomain_0b982980-b0d5-4c5b-944c-e070a0936b00" xlink:to="loc_icui_ShortTermMember_8c04fd25-952b-4d73-a848-2d7636061236" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_LongTermMember_c3c16462-df72-4b5c-a3b2-9d79297a24c9" xlink:href="icui-20250930.xsd#icui_LongTermMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_icui_TimingDomain_0b982980-b0d5-4c5b-944c-e070a0936b00" xlink:to="loc_icui_LongTermMember_c3c16462-df72-4b5c-a3b2-9d79297a24c9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_85bd90b7-6ffb-4534-b954-c6640eaa2da5" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_4d199ced-b786-43f6-b026-58ca1fd6dc67" xlink:to="loc_srt_ProductOrServiceAxis_85bd90b7-6ffb-4534-b954-c6640eaa2da5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_85bd90b7-6ffb-4534-b954-c6640eaa2da5_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_85bd90b7-6ffb-4534-b954-c6640eaa2da5" xlink:to="loc_srt_ProductsAndServicesDomain_85bd90b7-6ffb-4534-b954-c6640eaa2da5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_b24391d2-a364-40f3-819b-fd02c466ca1f" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_85bd90b7-6ffb-4534-b954-c6640eaa2da5" xlink:to="loc_srt_ProductsAndServicesDomain_b24391d2-a364-40f3-819b-fd02c466ca1f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_EquipmentrevenueMember_e5b42c89-1a18-4b28-93b9-af263f07e6ce" xlink:href="icui-20250930.xsd#icui_EquipmentrevenueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_b24391d2-a364-40f3-819b-fd02c466ca1f" xlink:to="loc_icui_EquipmentrevenueMember_e5b42c89-1a18-4b28-93b9-af263f07e6ce" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_SoftwarerevenueMember_4cce0f65-91de-4f8c-80f7-38b676e638ef" xlink:href="icui-20250930.xsd#icui_SoftwarerevenueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_b24391d2-a364-40f3-819b-fd02c466ca1f" xlink:to="loc_icui_SoftwarerevenueMember_4cce0f65-91de-4f8c-80f7-38b676e638ef" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_GovernmentGrantRevenueMember_85795849-13d9-45e6-8872-a13d35349db8" xlink:href="icui-20250930.xsd#icui_GovernmentGrantRevenueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_b24391d2-a364-40f3-819b-fd02c466ca1f" xlink:to="loc_icui_GovernmentGrantRevenueMember_85795849-13d9-45e6-8872-a13d35349db8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_OtherDeferredRevenueMember_a2280edb-d2a9-438b-b844-880768d1ac32" xlink:href="icui-20250930.xsd#icui_OtherDeferredRevenueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_b24391d2-a364-40f3-819b-fd02c466ca1f" xlink:to="loc_icui_OtherDeferredRevenueMember_a2280edb-d2a9-438b-b844-880768d1ac32" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligation_53b5f87a-8d95-4620-9112-67d407ac1828" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueRemainingPerformanceObligation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_cba7c696-85fe-4cb7-9609-4d425d6645e3" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligation_53b5f87a-8d95-4620-9112-67d407ac1828" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.icumed.com/role/SegmentReportingDetails" xlink:type="simple" xlink:href="icui-20250930.xsd#SegmentReportingDetails"/>
  <link:definitionLink xlink:role="http://www.icumed.com/role/SegmentReportingDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_83d40a2e-1035-401b-ad0f-da48f2aa2fc7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_eb0d4da3-5699-4583-b71f-ae0292b8f86d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_83d40a2e-1035-401b-ad0f-da48f2aa2fc7" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_eb0d4da3-5699-4583-b71f-ae0292b8f86d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsAxis_fa8045d6-969d-417f-894b-8de17245d8a7" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidationItemsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_eb0d4da3-5699-4583-b71f-ae0292b8f86d" xlink:to="loc_srt_ConsolidationItemsAxis_fa8045d6-969d-417f-894b-8de17245d8a7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_fa8045d6-969d-417f-894b-8de17245d8a7_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidationItemsAxis_fa8045d6-969d-417f-894b-8de17245d8a7" xlink:to="loc_srt_ConsolidationItemsDomain_fa8045d6-969d-417f-894b-8de17245d8a7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_35ae4018-f963-41a1-8280-ae71fbddb22c" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidationItemsAxis_fa8045d6-969d-417f-894b-8de17245d8a7" xlink:to="loc_srt_ConsolidationItemsDomain_35ae4018-f963-41a1-8280-ae71fbddb22c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingSegmentsMember_25d34a3b-fd4b-43be-af25-727ed5977136" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingSegmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_35ae4018-f963-41a1-8280-ae71fbddb22c" xlink:to="loc_us-gaap_OperatingSegmentsMember_25d34a3b-fd4b-43be-af25-727ed5977136" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Revenues_8c4921c8-69c6-465b-9db0-940eb366525e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_Revenues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_83d40a2e-1035-401b-ad0f-da48f2aa2fc7" xlink:to="loc_us-gaap_Revenues_8c4921c8-69c6-465b-9db0-940eb366525e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ManufacturingCosts_b0354f1a-ebed-49a2-bf6b-5cf7ea2ca2e1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ManufacturingCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_83d40a2e-1035-401b-ad0f-da48f2aa2fc7" xlink:to="loc_us-gaap_ManufacturingCosts_b0354f1a-ebed-49a2-bf6b-5cf7ea2ca2e1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InventoryRecallExpense_c3d0cc09-fa6a-4fd0-81f2-69ab7bd7c136" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InventoryRecallExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_83d40a2e-1035-401b-ad0f-da48f2aa2fc7" xlink:to="loc_us-gaap_InventoryRecallExpense_c3d0cc09-fa6a-4fd0-81f2-69ab7bd7c136" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherCostAndExpenseOperating_694a773d-38d8-41d0-8d01-e1af2aa28e03" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherCostAndExpenseOperating"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_83d40a2e-1035-401b-ad0f-da48f2aa2fc7" xlink:to="loc_us-gaap_OtherCostAndExpenseOperating_694a773d-38d8-41d0-8d01-e1af2aa28e03" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SellingGeneralAndAdministrativeExpense_72f02e60-40f5-4d6c-ab2a-443729460a0a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SellingGeneralAndAdministrativeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_83d40a2e-1035-401b-ad0f-da48f2aa2fc7" xlink:to="loc_us-gaap_SellingGeneralAndAdministrativeExpense_72f02e60-40f5-4d6c-ab2a-443729460a0a" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentExpense_21c4237e-0c12-48ae-9b30-88611db93c56" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ResearchAndDevelopmentExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_83d40a2e-1035-401b-ad0f-da48f2aa2fc7" xlink:to="loc_us-gaap_ResearchAndDevelopmentExpense_21c4237e-0c12-48ae-9b30-88611db93c56" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_Restructuringandstrategictransactionexpense_3a88fb46-77cb-48a1-bdca-1756cf5f1367" xlink:href="icui-20250930.xsd#icui_Restructuringandstrategictransactionexpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_83d40a2e-1035-401b-ad0f-da48f2aa2fc7" xlink:to="loc_icui_Restructuringandstrategictransactionexpense_3a88fb46-77cb-48a1-bdca-1756cf5f1367" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingOtherItemAmount_9282147a-75ec-4a5e-bd4b-f1543a26a27b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentReportingOtherItemAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_83d40a2e-1035-401b-ad0f-da48f2aa2fc7" xlink:to="loc_us-gaap_SegmentReportingOtherItemAmount_9282147a-75ec-4a5e-bd4b-f1543a26a27b" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpenseNonoperating_ea3d1a68-423b-44a9-ab94-ca9c542e4557" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InterestExpenseNonoperating"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_83d40a2e-1035-401b-ad0f-da48f2aa2fc7" xlink:to="loc_us-gaap_InterestExpenseNonoperating_ea3d1a68-423b-44a9-ab94-ca9c542e4557" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_88b1a1d2-51f9-42bd-86c5-e2a07b59e8c0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxExpenseBenefit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_83d40a2e-1035-401b-ad0f-da48f2aa2fc7" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefit_88b1a1d2-51f9-42bd-86c5-e2a07b59e8c0" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromEquityMethodInvestments_321cef6e-2ade-4b3e-87a0-adaa7357a4cc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeLossFromEquityMethodInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_83d40a2e-1035-401b-ad0f-da48f2aa2fc7" xlink:to="loc_us-gaap_IncomeLossFromEquityMethodInvestments_321cef6e-2ade-4b3e-87a0-adaa7357a4cc" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_0a97fada-1d27-4337-819a-2a0f89f9fd4d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_83d40a2e-1035-401b-ad0f-da48f2aa2fc7" xlink:to="loc_us-gaap_NetIncomeLoss_0a97fada-1d27-4337-819a-2a0f89f9fd4d" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenuesFromExternalCustomersAndLongLivedAssetsLineItems_02a30a36-8ffa-4588-8396-4b27704af982" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenuesFromExternalCustomersAndLongLivedAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRevenuesFromExternalCustomersAndLongLivedAssetsTable_1708b686-5973-4421-a413-ba056234b2c7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfRevenuesFromExternalCustomersAndLongLivedAssetsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RevenuesFromExternalCustomersAndLongLivedAssetsLineItems_02a30a36-8ffa-4588-8396-4b27704af982" xlink:to="loc_us-gaap_ScheduleOfRevenuesFromExternalCustomersAndLongLivedAssetsTable_1708b686-5973-4421-a413-ba056234b2c7" xlink:type="arc" order="2" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementGeographicalAxis_7bef7481-6895-439a-b19a-dd9c36d6e3b0" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_StatementGeographicalAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRevenuesFromExternalCustomersAndLongLivedAssetsTable_1708b686-5973-4421-a413-ba056234b2c7" xlink:to="loc_srt_StatementGeographicalAxis_7bef7481-6895-439a-b19a-dd9c36d6e3b0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_7bef7481-6895-439a-b19a-dd9c36d6e3b0_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementGeographicalAxis_7bef7481-6895-439a-b19a-dd9c36d6e3b0" xlink:to="loc_srt_SegmentGeographicalDomain_7bef7481-6895-439a-b19a-dd9c36d6e3b0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_b71aadda-c3e0-435c-894b-8fa0f5e4c18c" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementGeographicalAxis_7bef7481-6895-439a-b19a-dd9c36d6e3b0" xlink:to="loc_srt_SegmentGeographicalDomain_b71aadda-c3e0-435c-894b-8fa0f5e4c18c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_CR_ed7c3009-3260-446f-8f20-f40ca535a7cc" xlink:href="https://xbrl.sec.gov/country/2025/country-2025.xsd#country_CR"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_b71aadda-c3e0-435c-894b-8fa0f5e4c18c" xlink:to="loc_country_CR_ed7c3009-3260-446f-8f20-f40ca535a7cc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_MX_b114052f-b090-4607-a83d-e42edfe5e1c0" xlink:href="https://xbrl.sec.gov/country/2025/country-2025.xsd#country_MX"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_b71aadda-c3e0-435c-894b-8fa0f5e4c18c" xlink:to="loc_country_MX_b114052f-b090-4607-a83d-e42edfe5e1c0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_OtherLATAMMember_41e5ca31-006f-40ae-920e-a28e0c40b165" xlink:href="icui-20250930.xsd#icui_OtherLATAMMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_b71aadda-c3e0-435c-894b-8fa0f5e4c18c" xlink:to="loc_icui_OtherLATAMMember_41e5ca31-006f-40ae-920e-a28e0c40b165" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_CA_e21f6fe0-6876-4ddd-8f3a-b1bca6e2bb59" xlink:href="https://xbrl.sec.gov/country/2025/country-2025.xsd#country_CA"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_b71aadda-c3e0-435c-894b-8fa0f5e4c18c" xlink:to="loc_country_CA_e21f6fe0-6876-4ddd-8f3a-b1bca6e2bb59" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_IT_87f5b191-c0a1-44fe-8935-cb4fa20e5ca9" xlink:href="https://xbrl.sec.gov/country/2025/country-2025.xsd#country_IT"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_b71aadda-c3e0-435c-894b-8fa0f5e4c18c" xlink:to="loc_country_IT_87f5b191-c0a1-44fe-8935-cb4fa20e5ca9" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_ES_ab8fd2f3-9c4b-494d-971a-87150d8fd374" xlink:href="https://xbrl.sec.gov/country/2025/country-2025.xsd#country_ES"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_b71aadda-c3e0-435c-894b-8fa0f5e4c18c" xlink:to="loc_country_ES_ab8fd2f3-9c4b-494d-971a-87150d8fd374" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_CZ_3e9eef81-3be4-46e3-88c2-5d4e176f6b81" xlink:href="https://xbrl.sec.gov/country/2025/country-2025.xsd#country_CZ"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_b71aadda-c3e0-435c-894b-8fa0f5e4c18c" xlink:to="loc_country_CZ_3e9eef81-3be4-46e3-88c2-5d4e176f6b81" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EuropeMember_73fe8957-3e49-4564-980f-ed8be777c53a" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_EuropeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_b71aadda-c3e0-435c-894b-8fa0f5e4c18c" xlink:to="loc_srt_EuropeMember_73fe8957-3e49-4564-980f-ed8be777c53a" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_AsiaPacificMember_9675a78f-a9d3-4217-a744-b09619133a56" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_AsiaPacificMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_b71aadda-c3e0-435c-894b-8fa0f5e4c18c" xlink:to="loc_srt_AsiaPacificMember_9675a78f-a9d3-4217-a744-b09619133a56" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_ForeignMember_779729ef-9086-45d7-99ff-1c9e0cfd1723" xlink:href="icui-20250930.xsd#icui_ForeignMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_b71aadda-c3e0-435c-894b-8fa0f5e4c18c" xlink:to="loc_icui_ForeignMember_779729ef-9086-45d7-99ff-1c9e0cfd1723" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_US_a06eac40-1b13-473d-a285-7b28621665e9" xlink:href="https://xbrl.sec.gov/country/2025/country-2025.xsd#country_US"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_b71aadda-c3e0-435c-894b-8fa0f5e4c18c" xlink:to="loc_country_US_a06eac40-1b13-473d-a285-7b28621665e9" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentGross_d143f19b-b6a1-4e94-bbb3-bd1d6b8b8af3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenuesFromExternalCustomersAndLongLivedAssetsLineItems_02a30a36-8ffa-4588-8396-4b27704af982" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentGross_d143f19b-b6a1-4e94-bbb3-bd1d6b8b8af3" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.icumed.com/role/LeasesTextDetails" xlink:type="simple" xlink:href="icui-20250930.xsd#LeasesTextDetails"/>
  <link:definitionLink xlink:role="http://www.icumed.com/role/LeasesTextDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeLeaseDescriptionLineItems_db4796ce-ba93-4e6a-b636-82669f021c5c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LesseeLeaseDescriptionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeLeaseDescriptionTable_c3e77d4c-2521-47ff-805d-4cebef9bf287" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LesseeLeaseDescriptionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_db4796ce-ba93-4e6a-b636-82669f021c5c" xlink:to="loc_us-gaap_LesseeLeaseDescriptionTable_c3e77d4c-2521-47ff-805d-4cebef9bf287" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_1a64a445-df7f-4661-b57e-d0911519c1dd" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LesseeLeaseDescriptionTable_c3e77d4c-2521-47ff-805d-4cebef9bf287" xlink:to="loc_srt_RangeAxis_1a64a445-df7f-4661-b57e-d0911519c1dd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_1a64a445-df7f-4661-b57e-d0911519c1dd_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_1a64a445-df7f-4661-b57e-d0911519c1dd" xlink:to="loc_srt_RangeMember_1a64a445-df7f-4661-b57e-d0911519c1dd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_2d07219f-98b0-4f09-b6c7-463d7b342d96" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_1a64a445-df7f-4661-b57e-d0911519c1dd" xlink:to="loc_srt_RangeMember_2d07219f-98b0-4f09-b6c7-463d7b342d96" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_fa3d206b-db4d-4922-ae4b-1eff3798f72a" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_2d07219f-98b0-4f09-b6c7-463d7b342d96" xlink:to="loc_srt_MinimumMember_fa3d206b-db4d-4922-ae4b-1eff3798f72a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_6f022d29-29ef-49b3-8c1e-e8471aa7e814" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_2d07219f-98b0-4f09-b6c7-463d7b342d96" xlink:to="loc_srt_MaximumMember_6f022d29-29ef-49b3-8c1e-e8471aa7e814" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeOperatingLeaseTermOfContract_f832e49b-9fb3-4a6e-bd74-c72fd0119c94" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LesseeOperatingLeaseTermOfContract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_db4796ce-ba93-4e6a-b636-82669f021c5c" xlink:to="loc_us-gaap_LesseeOperatingLeaseTermOfContract_f832e49b-9fb3-4a6e-bd74-c72fd0119c94" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_Optiontoextendinyears_ba911e76-e8f7-403a-8ef1-e244afd39dcf" xlink:href="icui-20250930.xsd#icui_Optiontoextendinyears"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_db4796ce-ba93-4e6a-b636-82669f021c5c" xlink:to="loc_icui_Optiontoextendinyears_ba911e76-e8f7-403a-8ef1-e244afd39dcf" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.icumed.com/role/DerivativeFinancialInstrumentsForeignExchangeForwardContractsDetails" xlink:type="simple" xlink:href="icui-20250930.xsd#DerivativeFinancialInstrumentsForeignExchangeForwardContractsDetails"/>
  <link:definitionLink xlink:role="http://www.icumed.com/role/DerivativeFinancialInstrumentsForeignExchangeForwardContractsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLineItems_1e6a3b26-60b1-4414-bc61-1ce81cf9f3ee" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeTable_46b5646b-d964-40ea-b203-55eda14906eb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeLineItems_1e6a3b26-60b1-4414-bc61-1ce81cf9f3ee" xlink:to="loc_us-gaap_DerivativeTable_46b5646b-d964-40ea-b203-55eda14906eb" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CurrencyAxis_851d7f95-176d-495c-bc1c-c78f30c3c3b2" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_CurrencyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_46b5646b-d964-40ea-b203-55eda14906eb" xlink:to="loc_srt_CurrencyAxis_851d7f95-176d-495c-bc1c-c78f30c3c3b2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_currency_AllCurrenciesDomain_851d7f95-176d-495c-bc1c-c78f30c3c3b2_default" xlink:href="https://xbrl.sec.gov/currency/2025/currency-2025.xsd#currency_AllCurrenciesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CurrencyAxis_851d7f95-176d-495c-bc1c-c78f30c3c3b2" xlink:to="loc_currency_AllCurrenciesDomain_851d7f95-176d-495c-bc1c-c78f30c3c3b2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_currency_AllCurrenciesDomain_2a52ae48-fdc4-484a-b45c-097566080470" xlink:href="https://xbrl.sec.gov/currency/2025/currency-2025.xsd#currency_AllCurrenciesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CurrencyAxis_851d7f95-176d-495c-bc1c-c78f30c3c3b2" xlink:to="loc_currency_AllCurrenciesDomain_2a52ae48-fdc4-484a-b45c-097566080470" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_currency_CAD_68ae1ec3-5593-4d59-8182-679d79861237" xlink:href="https://xbrl.sec.gov/currency/2025/currency-2025.xsd#currency_CAD"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_currency_AllCurrenciesDomain_2a52ae48-fdc4-484a-b45c-097566080470" xlink:to="loc_currency_CAD_68ae1ec3-5593-4d59-8182-679d79861237" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_currency_EUR_fc9bb481-7657-411e-be48-fd7db3b6c0b2" xlink:href="https://xbrl.sec.gov/currency/2025/currency-2025.xsd#currency_EUR"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_currency_AllCurrenciesDomain_2a52ae48-fdc4-484a-b45c-097566080470" xlink:to="loc_currency_EUR_fc9bb481-7657-411e-be48-fd7db3b6c0b2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_currency_MXN_204e36ff-bfa2-4da1-9369-c0c5c3536ce7" xlink:href="https://xbrl.sec.gov/currency/2025/currency-2025.xsd#currency_MXN"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_currency_AllCurrenciesDomain_2a52ae48-fdc4-484a-b45c-097566080470" xlink:to="loc_currency_MXN_204e36ff-bfa2-4da1-9369-c0c5c3536ce7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_currency_USD_7c49c2aa-6a93-43ad-b2cd-5500a7d8c316" xlink:href="https://xbrl.sec.gov/currency/2025/currency-2025.xsd#currency_USD"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_currency_AllCurrenciesDomain_2a52ae48-fdc4-484a-b45c-097566080470" xlink:to="loc_currency_USD_7c49c2aa-6a93-43ad-b2cd-5500a7d8c316" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OtherCurrencyMember_666130da-8d1b-4dc1-a688-4f0c25c6eac8" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_OtherCurrencyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_currency_AllCurrenciesDomain_2a52ae48-fdc4-484a-b45c-097566080470" xlink:to="loc_srt_OtherCurrencyMember_666130da-8d1b-4dc1-a688-4f0c25c6eac8" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_currency_JPY_0c371844-0564-4621-8172-7bc4810c9180" xlink:href="https://xbrl.sec.gov/currency/2025/currency-2025.xsd#currency_JPY"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_currency_AllCurrenciesDomain_2a52ae48-fdc4-484a-b45c-097566080470" xlink:to="loc_currency_JPY_0c371844-0564-4621-8172-7bc4810c9180" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_currency_AUD_13c6615f-29cd-4d65-835f-fc65f299dd82" xlink:href="https://xbrl.sec.gov/currency/2025/currency-2025.xsd#currency_AUD"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_currency_AllCurrenciesDomain_2a52ae48-fdc4-484a-b45c-097566080470" xlink:to="loc_currency_AUD_13c6615f-29cd-4d65-835f-fc65f299dd82" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeNotionalAmount_653e8ba8-8e5a-48e2-80db-b613385ec13f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeNotionalAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_1e6a3b26-60b1-4414-bc61-1ce81cf9f3ee" xlink:to="loc_us-gaap_DerivativeNotionalAmount_653e8ba8-8e5a-48e2-80db-b613385ec13f" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.icumed.com/role/DerivativeFinancialInstrumentsInterestRateSwapsDetails" xlink:type="simple" xlink:href="icui-20250930.xsd#DerivativeFinancialInstrumentsInterestRateSwapsDetails"/>
  <link:definitionLink xlink:role="http://www.icumed.com/role/DerivativeFinancialInstrumentsInterestRateSwapsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLineItems_222eaab8-bf51-4373-8777-8327be8feac2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeTable_a6aba46f-d126-41b6-bb34-4eafd76f8d6a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeLineItems_222eaab8-bf51-4373-8777-8327be8feac2" xlink:to="loc_us-gaap_DerivativeTable_a6aba46f-d126-41b6-bb34-4eafd76f8d6a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_8b92758a-8c16-4c90-9b67-5fbe8f50e80b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_a6aba46f-d126-41b6-bb34-4eafd76f8d6a" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_8b92758a-8c16-4c90-9b67-5fbe8f50e80b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_8b92758a-8c16-4c90-9b67-5fbe8f50e80b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_8b92758a-8c16-4c90-9b67-5fbe8f50e80b" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_8b92758a-8c16-4c90-9b67-5fbe8f50e80b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_1f5efe51-4209-46f9-b376-ed3e20c3e770" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_8b92758a-8c16-4c90-9b67-5fbe8f50e80b" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_1f5efe51-4209-46f9-b376-ed3e20c3e770" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateSwapMember_6872c022-dab5-48e7-a9a0-46b87b19d018" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InterestRateSwapMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_1f5efe51-4209-46f9-b376-ed3e20c3e770" xlink:to="loc_us-gaap_InterestRateSwapMember_6872c022-dab5-48e7-a9a0-46b87b19d018" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_TermLoanAxis_45a2d09d-ea17-456d-bfa4-b67542344f11" xlink:href="icui-20250930.xsd#icui_TermLoanAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_a6aba46f-d126-41b6-bb34-4eafd76f8d6a" xlink:to="loc_icui_TermLoanAxis_45a2d09d-ea17-456d-bfa4-b67542344f11" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_TermLoanDomain_45a2d09d-ea17-456d-bfa4-b67542344f11_default" xlink:href="icui-20250930.xsd#icui_TermLoanDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_icui_TermLoanAxis_45a2d09d-ea17-456d-bfa4-b67542344f11" xlink:to="loc_icui_TermLoanDomain_45a2d09d-ea17-456d-bfa4-b67542344f11_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_TermLoanDomain_dd9f22da-d367-46c2-8cfb-4608aad317d6" xlink:href="icui-20250930.xsd#icui_TermLoanDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_icui_TermLoanAxis_45a2d09d-ea17-456d-bfa4-b67542344f11" xlink:to="loc_icui_TermLoanDomain_dd9f22da-d367-46c2-8cfb-4608aad317d6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_TermLoanAMember_ffa16880-fca7-453b-b954-9c218ceec0fb" xlink:href="icui-20250930.xsd#icui_TermLoanAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_icui_TermLoanDomain_dd9f22da-d367-46c2-8cfb-4608aad317d6" xlink:to="loc_icui_TermLoanAMember_ffa16880-fca7-453b-b954-9c218ceec0fb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_TermLoanBMember_dfcb24b3-e1dd-45d7-ab51-36d187bc4897" xlink:href="icui-20250930.xsd#icui_TermLoanBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_icui_TermLoanDomain_dd9f22da-d367-46c2-8cfb-4608aad317d6" xlink:to="loc_icui_TermLoanBMember_dfcb24b3-e1dd-45d7-ab51-36d187bc4897" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_Swap3TermLoanABMember_12070820-ff72-44a0-926c-1c118aaf7150" xlink:href="icui-20250930.xsd#icui_Swap3TermLoanABMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_icui_TermLoanDomain_dd9f22da-d367-46c2-8cfb-4608aad317d6" xlink:to="loc_icui_Swap3TermLoanABMember_12070820-ff72-44a0-926c-1c118aaf7150" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_Swap3Member_af804346-5eba-40a3-a310-74d2bde6afd1" xlink:href="icui-20250930.xsd#icui_Swap3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_icui_TermLoanDomain_dd9f22da-d367-46c2-8cfb-4608aad317d6" xlink:to="loc_icui_Swap3Member_af804346-5eba-40a3-a310-74d2bde6afd1" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeNotionalAmount_8df0b024-2b8c-4e48-96a4-541093820078" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeNotionalAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_222eaab8-bf51-4373-8777-8327be8feac2" xlink:to="loc_us-gaap_DerivativeNotionalAmount_8df0b024-2b8c-4e48-96a4-541093820078" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_InterestRateSwapEndingNotionalValue_79e71bb6-3b70-4b82-93e8-26b54c8898e6" xlink:href="icui-20250930.xsd#icui_InterestRateSwapEndingNotionalValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_222eaab8-bf51-4373-8777-8327be8feac2" xlink:to="loc_icui_InterestRateSwapEndingNotionalValue_79e71bb6-3b70-4b82-93e8-26b54c8898e6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeFixedInterestRate_470cde42-581f-4a14-bd9c-b84947694c7a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeFixedInterestRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_222eaab8-bf51-4373-8777-8327be8feac2" xlink:to="loc_us-gaap_DerivativeFixedInterestRate_470cde42-581f-4a14-bd9c-b84947694c7a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_DerivativeVariableRateFloor_ea188e45-6ded-4ee0-8b18-e99ec60cd639" xlink:href="icui-20250930.xsd#icui_DerivativeVariableRateFloor"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_222eaab8-bf51-4373-8777-8327be8feac2" xlink:to="loc_icui_DerivativeVariableRateFloor_ea188e45-6ded-4ee0-8b18-e99ec60cd639" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.icumed.com/role/DerivativeFinancialInstrumentsDerivativeInstrumentsandHedgingActivitiesFVofDerivativeInstrumentsIncludedWithinConsolidatedBalanceSheetDetails" xlink:type="simple" xlink:href="icui-20250930.xsd#DerivativeFinancialInstrumentsDerivativeInstrumentsandHedgingActivitiesFVofDerivativeInstrumentsIncludedWithinConsolidatedBalanceSheetDetails"/>
  <link:definitionLink xlink:role="http://www.icumed.com/role/DerivativeFinancialInstrumentsDerivativeInstrumentsandHedgingActivitiesFVofDerivativeInstrumentsIncludedWithinConsolidatedBalanceSheetDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativesFairValueLineItems_72c6db6f-3916-4c3d-8a47-e56185d8ec6e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativesFairValueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValuesDerivativesBalanceSheetLocationByDerivativeContractTypeByHedgingDesignationTable_5d2eb36a-8462-4d6a-b640-068580f927ea" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValuesDerivativesBalanceSheetLocationByDerivativeContractTypeByHedgingDesignationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativesFairValueLineItems_72c6db6f-3916-4c3d-8a47-e56185d8ec6e" xlink:to="loc_us-gaap_FairValuesDerivativesBalanceSheetLocationByDerivativeContractTypeByHedgingDesignationTable_5d2eb36a-8462-4d6a-b640-068580f927ea" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_001c2119-743e-4d63-8f9d-24f3cb6ea774" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValuesDerivativesBalanceSheetLocationByDerivativeContractTypeByHedgingDesignationTable_5d2eb36a-8462-4d6a-b640-068580f927ea" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_001c2119-743e-4d63-8f9d-24f3cb6ea774" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_001c2119-743e-4d63-8f9d-24f3cb6ea774_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_001c2119-743e-4d63-8f9d-24f3cb6ea774" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_001c2119-743e-4d63-8f9d-24f3cb6ea774_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_21bc29d8-06d7-4a8e-8fd1-42dc61235196" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_001c2119-743e-4d63-8f9d-24f3cb6ea774" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_21bc29d8-06d7-4a8e-8fd1-42dc61235196" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignExchangeContractMember_5b3300e4-47b3-41a2-8793-15dd9c6a380a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ForeignExchangeContractMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_21bc29d8-06d7-4a8e-8fd1-42dc61235196" xlink:to="loc_us-gaap_ForeignExchangeContractMember_5b3300e4-47b3-41a2-8793-15dd9c6a380a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateSwapMember_91999d5a-1041-4064-9502-a743ed090d28" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InterestRateSwapMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_21bc29d8-06d7-4a8e-8fd1-42dc61235196" xlink:to="loc_us-gaap_InterestRateSwapMember_91999d5a-1041-4064-9502-a743ed090d28" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeAssetCurrentStatementOfFinancialPositionExtensibleEnumeration_dc604368-bc02-4277-900c-b51497f5c4af" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeAssetCurrentStatementOfFinancialPositionExtensibleEnumeration"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativesFairValueLineItems_72c6db6f-3916-4c3d-8a47-e56185d8ec6e" xlink:to="loc_us-gaap_DerivativeAssetCurrentStatementOfFinancialPositionExtensibleEnumeration_dc604368-bc02-4277-900c-b51497f5c4af" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeAssetsCurrent_a75a8697-d175-4f40-bfbd-316e984a143b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeAssetsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativesFairValueLineItems_72c6db6f-3916-4c3d-8a47-e56185d8ec6e" xlink:to="loc_us-gaap_DerivativeAssetsCurrent_a75a8697-d175-4f40-bfbd-316e984a143b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeAssetNoncurrentStatementOfFinancialPositionExtensibleEnumeration_8517f058-08be-4f5f-b17f-0ca7a52f31b5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeAssetNoncurrentStatementOfFinancialPositionExtensibleEnumeration"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativesFairValueLineItems_72c6db6f-3916-4c3d-8a47-e56185d8ec6e" xlink:to="loc_us-gaap_DerivativeAssetNoncurrentStatementOfFinancialPositionExtensibleEnumeration_8517f058-08be-4f5f-b17f-0ca7a52f31b5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeAssetsNoncurrent_a5f3fdbd-9da4-44ca-a04d-77ec69903654" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeAssetsNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativesFairValueLineItems_72c6db6f-3916-4c3d-8a47-e56185d8ec6e" xlink:to="loc_us-gaap_DerivativeAssetsNoncurrent_a5f3fdbd-9da4-44ca-a04d-77ec69903654" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeAssets_b5efc0f8-efd5-45e1-968d-afa327163451" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativesFairValueLineItems_72c6db6f-3916-4c3d-8a47-e56185d8ec6e" xlink:to="loc_us-gaap_DerivativeAssets_b5efc0f8-efd5-45e1-968d-afa327163451" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLiabilityCurrentStatementOfFinancialPositionExtensibleEnumeration_a289018d-be4a-4a04-aff6-96cd407dec95" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeLiabilityCurrentStatementOfFinancialPositionExtensibleEnumeration"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativesFairValueLineItems_72c6db6f-3916-4c3d-8a47-e56185d8ec6e" xlink:to="loc_us-gaap_DerivativeLiabilityCurrentStatementOfFinancialPositionExtensibleEnumeration_a289018d-be4a-4a04-aff6-96cd407dec95" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLiabilitiesCurrent_6d60d801-9ac7-461a-accd-aa9efa9105d1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeLiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativesFairValueLineItems_72c6db6f-3916-4c3d-8a47-e56185d8ec6e" xlink:to="loc_us-gaap_DerivativeLiabilitiesCurrent_6d60d801-9ac7-461a-accd-aa9efa9105d1" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLiabilityNoncurrentStatementOfFinancialPositionExtensibleEnumeration_fdea984a-bec6-4a39-af97-8a3ab83768d5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeLiabilityNoncurrentStatementOfFinancialPositionExtensibleEnumeration"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativesFairValueLineItems_72c6db6f-3916-4c3d-8a47-e56185d8ec6e" xlink:to="loc_us-gaap_DerivativeLiabilityNoncurrentStatementOfFinancialPositionExtensibleEnumeration_fdea984a-bec6-4a39-af97-8a3ab83768d5" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLiabilitiesNoncurrent_02b20bc0-7f84-428e-96c9-1e997a142f97" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeLiabilitiesNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativesFairValueLineItems_72c6db6f-3916-4c3d-8a47-e56185d8ec6e" xlink:to="loc_us-gaap_DerivativeLiabilitiesNoncurrent_02b20bc0-7f84-428e-96c9-1e997a142f97" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLiabilities_e1f84334-2dcf-4ca1-8ddb-f5effa23c647" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativesFairValueLineItems_72c6db6f-3916-4c3d-8a47-e56185d8ec6e" xlink:to="loc_us-gaap_DerivativeLiabilities_e1f84334-2dcf-4ca1-8ddb-f5effa23c647" xlink:type="arc" order="9"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.icumed.com/role/DerivativeFinancialInstrumentsDerivativeInstrumentsandHedgingActivitiesCashFlowHedgeActivityIncludedinAccumulatedOtherComprehensiveIncomeLossDetails" xlink:type="simple" xlink:href="icui-20250930.xsd#DerivativeFinancialInstrumentsDerivativeInstrumentsandHedgingActivitiesCashFlowHedgeActivityIncludedinAccumulatedOtherComprehensiveIncomeLossDetails"/>
  <link:definitionLink xlink:role="http://www.icumed.com/role/DerivativeFinancialInstrumentsDerivativeInstrumentsandHedgingActivitiesCashFlowHedgeActivityIncludedinAccumulatedOtherComprehensiveIncomeLossDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems_a3df1d77-cb6b-4c8e-8f32-2bbd6aca8e54" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable_0bfd6755-de6d-47f3-b48e-7fd742eb5a29" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems_a3df1d77-cb6b-4c8e-8f32-2bbd6aca8e54" xlink:to="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable_0bfd6755-de6d-47f3-b48e-7fd742eb5a29" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_45129e85-0147-4dec-81db-b0859f524c58" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable_0bfd6755-de6d-47f3-b48e-7fd742eb5a29" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_45129e85-0147-4dec-81db-b0859f524c58" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_45129e85-0147-4dec-81db-b0859f524c58_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_45129e85-0147-4dec-81db-b0859f524c58" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_45129e85-0147-4dec-81db-b0859f524c58_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_0a4cb5f8-d156-4761-af4e-287a091384a4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_45129e85-0147-4dec-81db-b0859f524c58" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_0a4cb5f8-d156-4761-af4e-287a091384a4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignExchangeContractMember_3f101cf4-bd11-4e61-b9e6-46f6eeaab100" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ForeignExchangeContractMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_0a4cb5f8-d156-4761-af4e-287a091384a4" xlink:to="loc_us-gaap_ForeignExchangeContractMember_3f101cf4-bd11-4e61-b9e6-46f6eeaab100" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateSwapMember_af11c08f-9100-4035-8a40-a73e24ec6f57" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InterestRateSwapMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_0a4cb5f8-d156-4761-af4e-287a091384a4" xlink:to="loc_us-gaap_InterestRateSwapMember_af11c08f-9100-4035-8a40-a73e24ec6f57" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossBeforeTax_9378cc4d-3d6d-4510-a034-b6ea1ff4da5c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherComprehensiveIncomeLossBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems_a3df1d77-cb6b-4c8e-8f32-2bbd6aca8e54" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossBeforeTax_9378cc4d-3d6d-4510-a034-b6ea1ff4da5c" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.icumed.com/role/DerivativeFinancialInstrumentsDerivativeInstrumentsandHedgingActivitiesAmountsAffectingConsolidatedStatementsofIncomeDetails" xlink:type="simple" xlink:href="icui-20250930.xsd#DerivativeFinancialInstrumentsDerivativeInstrumentsandHedgingActivitiesAmountsAffectingConsolidatedStatementsofIncomeDetails"/>
  <link:definitionLink xlink:role="http://www.icumed.com/role/DerivativeFinancialInstrumentsDerivativeInstrumentsandHedgingActivitiesAmountsAffectingConsolidatedStatementsofIncomeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_ed8212cf-d93a-47e2-994f-602766467406" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeInstrumentsGainLossLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_20286095-e66e-4743-b444-c02cd05f2592" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_ed8212cf-d93a-47e2-994f-602766467406" xlink:to="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_20286095-e66e-4743-b444-c02cd05f2592" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_95fd6317-b6f1-4ee7-bbb8-7b63ebc139e5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_20286095-e66e-4743-b444-c02cd05f2592" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_95fd6317-b6f1-4ee7-bbb8-7b63ebc139e5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_95fd6317-b6f1-4ee7-bbb8-7b63ebc139e5_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_95fd6317-b6f1-4ee7-bbb8-7b63ebc139e5" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_95fd6317-b6f1-4ee7-bbb8-7b63ebc139e5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_63c83dcd-0115-41b3-8e2c-293a3a19eeda" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_95fd6317-b6f1-4ee7-bbb8-7b63ebc139e5" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_63c83dcd-0115-41b3-8e2c-293a3a19eeda" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignExchangeContractMember_9779bba4-3b14-4be4-8881-da0654279e35" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ForeignExchangeContractMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_63c83dcd-0115-41b3-8e2c-293a3a19eeda" xlink:to="loc_us-gaap_ForeignExchangeContractMember_9779bba4-3b14-4be4-8881-da0654279e35" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateSwapMember_72993336-6ac3-4f1b-81df-4ed8588ffd8e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InterestRateSwapMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_63c83dcd-0115-41b3-8e2c-293a3a19eeda" xlink:to="loc_us-gaap_InterestRateSwapMember_72993336-6ac3-4f1b-81df-4ed8588ffd8e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationAxis_b7436510-08ef-4744-8767-716859a7e024" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_20286095-e66e-4743-b444-c02cd05f2592" xlink:to="loc_us-gaap_IncomeStatementLocationAxis_b7436510-08ef-4744-8767-716859a7e024" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_b7436510-08ef-4744-8767-716859a7e024_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_b7436510-08ef-4744-8767-716859a7e024" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_b7436510-08ef-4744-8767-716859a7e024_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_29825b57-ff04-4aec-835b-0d65462c2807" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_b7436510-08ef-4744-8767-716859a7e024" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_29825b57-ff04-4aec-835b-0d65462c2807" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerMember_ea6e4904-033c-4a23-8fa1-e358e644724f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueFromContractWithCustomerMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_29825b57-ff04-4aec-835b-0d65462c2807" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerMember_ea6e4904-033c-4a23-8fa1-e358e644724f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfSalesMember_8d9fc0ba-f887-419a-84a9-ae07a8b46b68" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CostOfSalesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_29825b57-ff04-4aec-835b-0d65462c2807" xlink:to="loc_us-gaap_CostOfSalesMember_8d9fc0ba-f887-419a-84a9-ae07a8b46b68" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpenseMember_aeb1711e-37bb-4283-b01f-218a46e4a9bb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InterestExpenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_29825b57-ff04-4aec-835b-0d65462c2807" xlink:to="loc_us-gaap_InterestExpenseMember_aeb1711e-37bb-4283-b01f-218a46e4a9bb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_84266024-9528-4c11-a0f8-7359f5f004dd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_20286095-e66e-4743-b444-c02cd05f2592" xlink:to="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_84266024-9528-4c11-a0f8-7359f5f004dd" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingRelationshipDomain_84266024-9528-4c11-a0f8-7359f5f004dd_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_HedgingRelationshipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_84266024-9528-4c11-a0f8-7359f5f004dd" xlink:to="loc_us-gaap_HedgingRelationshipDomain_84266024-9528-4c11-a0f8-7359f5f004dd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingRelationshipDomain_86e5dd93-7e86-44bd-862b-3bab5ae33e2a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_HedgingRelationshipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_84266024-9528-4c11-a0f8-7359f5f004dd" xlink:to="loc_us-gaap_HedgingRelationshipDomain_86e5dd93-7e86-44bd-862b-3bab5ae33e2a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashFlowHedgingMember_61b815f7-f0d2-4334-9ad3-2d1eb7a2ae22" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CashFlowHedgingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingRelationshipDomain_86e5dd93-7e86-44bd-862b-3bab5ae33e2a" xlink:to="loc_us-gaap_CashFlowHedgingMember_61b815f7-f0d2-4334-9ad3-2d1eb7a2ae22" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainLossOnDerivativeInstrumentsNetPretax_f0a2b042-ed94-4d7a-a672-a4e2f2541f58" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GainLossOnDerivativeInstrumentsNetPretax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_ed8212cf-d93a-47e2-994f-602766467406" xlink:to="loc_us-gaap_GainLossOnDerivativeInstrumentsNetPretax_f0a2b042-ed94-4d7a-a672-a4e2f2541f58" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignCurrencyCashFlowHedgeGainLossToBeReclassifiedDuringNext12Months_71a388cb-c010-4500-bb99-9011b9f34417" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ForeignCurrencyCashFlowHedgeGainLossToBeReclassifiedDuringNext12Months"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_ed8212cf-d93a-47e2-994f-602766467406" xlink:to="loc_us-gaap_ForeignCurrencyCashFlowHedgeGainLossToBeReclassifiedDuringNext12Months_71a388cb-c010-4500-bb99-9011b9f34417" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateCashFlowHedgeGainLossToBeReclassifiedDuringNext12MonthsNet_d2bb27cd-dca6-4201-bc3f-7851bc3a8602" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InterestRateCashFlowHedgeGainLossToBeReclassifiedDuringNext12MonthsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_ed8212cf-d93a-47e2-994f-602766467406" xlink:to="loc_us-gaap_InterestRateCashFlowHedgeGainLossToBeReclassifiedDuringNext12MonthsNet_d2bb27cd-dca6-4201-bc3f-7851bc3a8602" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.icumed.com/role/FairValueMeasuresandDisclosuresDetails" xlink:type="simple" xlink:href="icui-20250930.xsd#FairValueMeasuresandDisclosuresDetails"/>
  <link:definitionLink xlink:role="http://www.icumed.com/role/FairValueMeasuresandDisclosuresDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_8f204417-64c7-4c9c-9b97-ca1636ba097e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable_ef287e31-8400-4405-8bcf-b148d955d0b1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_8f204417-64c7-4c9c-9b97-ca1636ba097e" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable_ef287e31-8400-4405-8bcf-b148d955d0b1" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_d3cea21d-19a6-4800-a097-2edd0e4845d9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable_ef287e31-8400-4405-8bcf-b148d955d0b1" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_d3cea21d-19a6-4800-a097-2edd0e4845d9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_d3cea21d-19a6-4800-a097-2edd0e4845d9_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_d3cea21d-19a6-4800-a097-2edd0e4845d9" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_d3cea21d-19a6-4800-a097-2edd0e4845d9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_e9564e67-f29c-40b5-89a0-db3188a2eef1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_d3cea21d-19a6-4800-a097-2edd0e4845d9" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_e9564e67-f29c-40b5-89a0-db3188a2eef1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_SmithsMedicalMember_5f634bfd-0790-4a0a-bba2-4eb89f62ee95" xlink:href="icui-20250930.xsd#icui_SmithsMedicalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_e9564e67-f29c-40b5-89a0-db3188a2eef1" xlink:to="loc_icui_SmithsMedicalMember_5f634bfd-0790-4a0a-bba2-4eb89f62ee95" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_ForeignInfusionSystemSupplierMember_e09b9018-1d6e-48c7-a5ec-5e9dd59be834" xlink:href="icui-20250930.xsd#icui_ForeignInfusionSystemSupplierMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_e9564e67-f29c-40b5-89a0-db3188a2eef1" xlink:to="loc_icui_ForeignInfusionSystemSupplierMember_e09b9018-1d6e-48c7-a5ec-5e9dd59be834" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_InternationalDistributorMember_a66a676d-02f8-41d1-8874-342a733ac7c4" xlink:href="icui-20250930.xsd#icui_InternationalDistributorMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_e9564e67-f29c-40b5-89a0-db3188a2eef1" xlink:to="loc_icui_InternationalDistributorMember_a66a676d-02f8-41d1-8874-342a733ac7c4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContingentConsiderationByTypeAxis_2ae2e0b4-c282-4168-9693-ae0d77e99397" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ContingentConsiderationByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable_ef287e31-8400-4405-8bcf-b148d955d0b1" xlink:to="loc_us-gaap_ContingentConsiderationByTypeAxis_2ae2e0b4-c282-4168-9693-ae0d77e99397" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContingentConsiderationTypeDomain_2ae2e0b4-c282-4168-9693-ae0d77e99397_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ContingentConsiderationTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ContingentConsiderationByTypeAxis_2ae2e0b4-c282-4168-9693-ae0d77e99397" xlink:to="loc_us-gaap_ContingentConsiderationTypeDomain_2ae2e0b4-c282-4168-9693-ae0d77e99397_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContingentConsiderationTypeDomain_6c47c59d-33d9-4433-8fff-419b4e4b51c5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ContingentConsiderationTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ContingentConsiderationByTypeAxis_2ae2e0b4-c282-4168-9693-ae0d77e99397" xlink:to="loc_us-gaap_ContingentConsiderationTypeDomain_6c47c59d-33d9-4433-8fff-419b4e4b51c5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilityMember_c1ed5407-75c4-4ba7-b077-9fe7b22804d6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LiabilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ContingentConsiderationTypeDomain_6c47c59d-33d9-4433-8fff-419b4e4b51c5" xlink:to="loc_us-gaap_LiabilityMember_c1ed5407-75c4-4ba7-b077-9fe7b22804d6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_Contingentconsiderationgross_02d53baa-778a-40dd-9bc2-b5f94f297992" xlink:href="icui-20250930.xsd#icui_Contingentconsiderationgross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_8f204417-64c7-4c9c-9b97-ca1636ba097e" xlink:to="loc_icui_Contingentconsiderationgross_02d53baa-778a-40dd-9bc2-b5f94f297992" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_OwnershipRequirementForEarnoutPayment_ac78a71b-bdaa-436f-bd5b-4f45317a5f59" xlink:href="icui-20250930.xsd#icui_OwnershipRequirementForEarnoutPayment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_8f204417-64c7-4c9c-9b97-ca1636ba097e" xlink:to="loc_icui_OwnershipRequirementForEarnoutPayment_ac78a71b-bdaa-436f-bd5b-4f45317a5f59" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue_27746675-09f1-4afd-affa-6c8dbf4b93ea" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_8f204417-64c7-4c9c-9b97-ca1636ba097e" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue_27746675-09f1-4afd-affa-6c8dbf4b93ea" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationContingentConsiderationArrangementsChangeInAmountOfContingentConsiderationLiability1_1ffdf2a6-bc2d-47bb-b17a-590b191a4348" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationContingentConsiderationArrangementsChangeInAmountOfContingentConsiderationLiability1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_8f204417-64c7-4c9c-9b97-ca1636ba097e" xlink:to="loc_us-gaap_BusinessCombinationContingentConsiderationArrangementsChangeInAmountOfContingentConsiderationLiability1_1ffdf2a6-bc2d-47bb-b17a-590b191a4348" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.icumed.com/role/FairValueMeasuresandDisclosuresLiabilitiesRecurringBasisUnobservableInputReconciliationRollForwardDetails" xlink:type="simple" xlink:href="icui-20250930.xsd#FairValueMeasuresandDisclosuresLiabilitiesRecurringBasisUnobservableInputReconciliationRollForwardDetails"/>
  <link:definitionLink xlink:role="http://www.icumed.com/role/FairValueMeasuresandDisclosuresLiabilitiesRecurringBasisUnobservableInputReconciliationRollForwardDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_a28f1912-7fbc-4aa2-8a94-5bf116cbe23e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable_1b68a327-89a6-4680-a44a-1585e78c623b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_a28f1912-7fbc-4aa2-8a94-5bf116cbe23e" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable_1b68a327-89a6-4680-a44a-1585e78c623b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_f554e3eb-614f-4476-9a0f-2de3c3358ab7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable_1b68a327-89a6-4680-a44a-1585e78c623b" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_f554e3eb-614f-4476-9a0f-2de3c3358ab7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_f554e3eb-614f-4476-9a0f-2de3c3358ab7_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_f554e3eb-614f-4476-9a0f-2de3c3358ab7" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_f554e3eb-614f-4476-9a0f-2de3c3358ab7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_3052b150-549a-44b9-bc98-fa84775a4eb0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_f554e3eb-614f-4476-9a0f-2de3c3358ab7" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_3052b150-549a-44b9-bc98-fa84775a4eb0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_SmithsMedicalMember_c4eb5274-9129-445b-b59d-ce1de3edd108" xlink:href="icui-20250930.xsd#icui_SmithsMedicalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_3052b150-549a-44b9-bc98-fa84775a4eb0" xlink:to="loc_icui_SmithsMedicalMember_c4eb5274-9129-445b-b59d-ce1de3edd108" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_ForeignInfusionSystemSupplierMember_1c076839-4e76-40fb-9b47-0d52fa73128f" xlink:href="icui-20250930.xsd#icui_ForeignInfusionSystemSupplierMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_3052b150-549a-44b9-bc98-fa84775a4eb0" xlink:to="loc_icui_ForeignInfusionSystemSupplierMember_1c076839-4e76-40fb-9b47-0d52fa73128f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_InternationalDistributorMember_d206fe50-bafe-4341-bd1a-b3b2cb80fab0" xlink:href="icui-20250930.xsd#icui_InternationalDistributorMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_3052b150-549a-44b9-bc98-fa84775a4eb0" xlink:to="loc_icui_InternationalDistributorMember_d206fe50-bafe-4341-bd1a-b3b2cb80fab0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationAxis_570f1bc0-4c01-4fe4-bf42-85770e8eee85" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable_1b68a327-89a6-4680-a44a-1585e78c623b" xlink:to="loc_us-gaap_IncomeStatementLocationAxis_570f1bc0-4c01-4fe4-bf42-85770e8eee85" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_570f1bc0-4c01-4fe4-bf42-85770e8eee85_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_570f1bc0-4c01-4fe4-bf42-85770e8eee85" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_570f1bc0-4c01-4fe4-bf42-85770e8eee85_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_0403f4b1-0043-4800-8184-7942c0bf4762" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_570f1bc0-4c01-4fe4-bf42-85770e8eee85" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_0403f4b1-0043-4800-8184-7942c0bf4762" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByLiabilityClassAxis_262b9c56-73e4-4c8c-a678-720b3823110f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueByLiabilityClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable_1b68a327-89a6-4680-a44a-1585e78c623b" xlink:to="loc_us-gaap_FairValueByLiabilityClassAxis_262b9c56-73e4-4c8c-a678-720b3823110f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_262b9c56-73e4-4c8c-a678-720b3823110f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByLiabilityClassAxis_262b9c56-73e4-4c8c-a678-720b3823110f" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_262b9c56-73e4-4c8c-a678-720b3823110f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_3a2e5cac-493c-4b0b-8908-c9cfc79608bb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByLiabilityClassAxis_262b9c56-73e4-4c8c-a678-720b3823110f" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_3a2e5cac-493c-4b0b-8908-c9cfc79608bb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLocationAxis_0ce6ca28-59aa-4e1f-ae4c-4ab1df1daeae" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherComprehensiveIncomeLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable_1b68a327-89a6-4680-a44a-1585e78c623b" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLocationAxis_0ce6ca28-59aa-4e1f-ae4c-4ab1df1daeae" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLocationDomain_0ce6ca28-59aa-4e1f-ae4c-4ab1df1daeae_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherComprehensiveIncomeLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_OtherComprehensiveIncomeLocationAxis_0ce6ca28-59aa-4e1f-ae4c-4ab1df1daeae" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLocationDomain_0ce6ca28-59aa-4e1f-ae4c-4ab1df1daeae_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLocationDomain_974ad95c-989c-4f85-aec4-6c8b1b7ff649" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherComprehensiveIncomeLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_OtherComprehensiveIncomeLocationAxis_0ce6ca28-59aa-4e1f-ae4c-4ab1df1daeae" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLocationDomain_974ad95c-989c-4f85-aec4-6c8b1b7ff649" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue_8cbaa4ab-5542-4d2e-b861-582674d0152c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_a28f1912-7fbc-4aa2-8a94-5bf116cbe23e" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue_8cbaa4ab-5542-4d2e-b861-582674d0152c" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.icumed.com/role/FairValueMeasuresandDisclosuresLiabilityMeasurementInputsDetails" xlink:type="simple" xlink:href="icui-20250930.xsd#FairValueMeasuresandDisclosuresLiabilityMeasurementInputsDetails"/>
  <link:definitionLink xlink:role="http://www.icumed.com/role/FairValueMeasuresandDisclosuresLiabilityMeasurementInputsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_203d6412-1889-424c-9193-52fbde290bb3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_3bc93769-73d5-42b2-8508-18bb87b9effd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_203d6412-1889-424c-9193-52fbde290bb3" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_3bc93769-73d5-42b2-8508-18bb87b9effd" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_f143b69a-ae88-458a-bb0a-e3fded190f46" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_3bc93769-73d5-42b2-8508-18bb87b9effd" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_f143b69a-ae88-458a-bb0a-e3fded190f46" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_f143b69a-ae88-458a-bb0a-e3fded190f46_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_f143b69a-ae88-458a-bb0a-e3fded190f46" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_f143b69a-ae88-458a-bb0a-e3fded190f46_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_d0f334c2-904f-4a68-ad5b-84e1fdbd2e8e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_f143b69a-ae88-458a-bb0a-e3fded190f46" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_d0f334c2-904f-4a68-ad5b-84e1fdbd2e8e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_SmithsMedicalMember_53eaa167-fd86-4f85-a13a-7e4bb805a79f" xlink:href="icui-20250930.xsd#icui_SmithsMedicalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_d0f334c2-904f-4a68-ad5b-84e1fdbd2e8e" xlink:to="loc_icui_SmithsMedicalMember_53eaa167-fd86-4f85-a13a-7e4bb805a79f" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.icumed.com/role/FairValueMeasuresandDisclosuresAssetsandLiabilitiesbyBalanceSheetGroupingDetails" xlink:type="simple" xlink:href="icui-20250930.xsd#FairValueMeasuresandDisclosuresAssetsandLiabilitiesbyBalanceSheetGroupingDetails"/>
  <link:definitionLink xlink:role="http://www.icumed.com/role/FairValueMeasuresandDisclosuresAssetsandLiabilitiesbyBalanceSheetGroupingDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_de2420a2-89de-4ff2-a1bc-28815e271b69" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByBalanceSheetGroupingTable_fef0564f-64ee-44a5-a28e-68392b62cde5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueByBalanceSheetGroupingTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_de2420a2-89de-4ff2-a1bc-28815e271b69" xlink:to="loc_us-gaap_FairValueByBalanceSheetGroupingTable_fef0564f-64ee-44a5-a28e-68392b62cde5" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_8f7fc098-4c4a-4794-b424-9d72c8e14635" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueByBalanceSheetGroupingTable_fef0564f-64ee-44a5-a28e-68392b62cde5" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_8f7fc098-4c4a-4794-b424-9d72c8e14635" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_8f7fc098-4c4a-4794-b424-9d72c8e14635_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_8f7fc098-4c4a-4794-b424-9d72c8e14635" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_8f7fc098-4c4a-4794-b424-9d72c8e14635_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_828e846b-e1ec-454a-9380-51951fb69db9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_8f7fc098-4c4a-4794-b424-9d72c8e14635" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_828e846b-e1ec-454a-9380-51951fb69db9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_da0ba2b9-af97-4f42-aed4-dc53ca839bf7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueInputsLevel1Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_828e846b-e1ec-454a-9380-51951fb69db9" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_da0ba2b9-af97-4f42-aed4-dc53ca839bf7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_eca69c5e-d5b7-40a7-a7bc-324c6202b650" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueInputsLevel2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_828e846b-e1ec-454a-9380-51951fb69db9" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_eca69c5e-d5b7-40a7-a7bc-324c6202b650" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_c384dbee-7c46-49e9-a294-c1bc1e866850" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_828e846b-e1ec-454a-9380-51951fb69db9" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_c384dbee-7c46-49e9-a294-c1bc1e866850" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationAxis_8ac74644-03bf-4b97-9c50-ff769fe73c3f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BalanceSheetLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueByBalanceSheetGroupingTable_fef0564f-64ee-44a5-a28e-68392b62cde5" xlink:to="loc_us-gaap_BalanceSheetLocationAxis_8ac74644-03bf-4b97-9c50-ff769fe73c3f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationDomain_8ac74644-03bf-4b97-9c50-ff769fe73c3f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BalanceSheetLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BalanceSheetLocationAxis_8ac74644-03bf-4b97-9c50-ff769fe73c3f" xlink:to="loc_us-gaap_BalanceSheetLocationDomain_8ac74644-03bf-4b97-9c50-ff769fe73c3f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationDomain_94c929ed-1b28-46ec-87d5-d7ba52e993b9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BalanceSheetLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BalanceSheetLocationAxis_8ac74644-03bf-4b97-9c50-ff769fe73c3f" xlink:to="loc_us-gaap_BalanceSheetLocationDomain_94c929ed-1b28-46ec-87d5-d7ba52e993b9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PrepaidExpensesAndOtherCurrentAssetsMember_386ffee0-b72c-42c0-95f3-1d4a3258223e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PrepaidExpensesAndOtherCurrentAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetLocationDomain_94c929ed-1b28-46ec-87d5-d7ba52e993b9" xlink:to="loc_us-gaap_PrepaidExpensesAndOtherCurrentAssetsMember_386ffee0-b72c-42c0-95f3-1d4a3258223e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByLiabilityClassAxis_e4a7f906-6eae-4993-8f57-49f12649c3a6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueByLiabilityClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueByBalanceSheetGroupingTable_fef0564f-64ee-44a5-a28e-68392b62cde5" xlink:to="loc_us-gaap_FairValueByLiabilityClassAxis_e4a7f906-6eae-4993-8f57-49f12649c3a6" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_e4a7f906-6eae-4993-8f57-49f12649c3a6_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByLiabilityClassAxis_e4a7f906-6eae-4993-8f57-49f12649c3a6" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_e4a7f906-6eae-4993-8f57-49f12649c3a6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_98c7b5e7-e535-49fb-9fc1-634f51df7857" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByLiabilityClassAxis_e4a7f906-6eae-4993-8f57-49f12649c3a6" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_98c7b5e7-e535-49fb-9fc1-634f51df7857" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesTotalMember_e62af501-a3de-400e-9120-abb2a443b17f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LiabilitiesTotalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_98c7b5e7-e535-49fb-9fc1-634f51df7857" xlink:to="loc_us-gaap_LiabilitiesTotalMember_e62af501-a3de-400e-9120-abb2a443b17f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentTypeAxis_6d694a18-96c1-4f77-9f45-0e072fc04ce1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InvestmentTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueByBalanceSheetGroupingTable_fef0564f-64ee-44a5-a28e-68392b62cde5" xlink:to="loc_us-gaap_InvestmentTypeAxis_6d694a18-96c1-4f77-9f45-0e072fc04ce1" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentTypeCategorizationMember_6d694a18-96c1-4f77-9f45-0e072fc04ce1_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InvestmentTypeCategorizationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_InvestmentTypeAxis_6d694a18-96c1-4f77-9f45-0e072fc04ce1" xlink:to="loc_us-gaap_InvestmentTypeCategorizationMember_6d694a18-96c1-4f77-9f45-0e072fc04ce1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentTypeCategorizationMember_3506a4da-8c53-4ec3-a7e8-5853ceddc0a5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InvestmentTypeCategorizationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_InvestmentTypeAxis_6d694a18-96c1-4f77-9f45-0e072fc04ce1" xlink:to="loc_us-gaap_InvestmentTypeCategorizationMember_3506a4da-8c53-4ec3-a7e8-5853ceddc0a5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_33a6de28-0482-4fd5-983f-b64a057120ce" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueByBalanceSheetGroupingTable_fef0564f-64ee-44a5-a28e-68392b62cde5" xlink:to="loc_us-gaap_FinancialInstrumentAxis_33a6de28-0482-4fd5-983f-b64a057120ce" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_33a6de28-0482-4fd5-983f-b64a057120ce_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_33a6de28-0482-4fd5-983f-b64a057120ce" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_33a6de28-0482-4fd5-983f-b64a057120ce_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_31730f1a-5334-4fa8-a7f0-afb6c1f38bac" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_33a6de28-0482-4fd5-983f-b64a057120ce" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_31730f1a-5334-4fa8-a7f0-afb6c1f38bac" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_ClassificationAxis_db756e46-6652-4b32-bc75-0009c0cc9a29" xlink:href="icui-20250930.xsd#icui_ClassificationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueByBalanceSheetGroupingTable_fef0564f-64ee-44a5-a28e-68392b62cde5" xlink:to="loc_icui_ClassificationAxis_db756e46-6652-4b32-bc75-0009c0cc9a29" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_ClassificationDomain_db756e46-6652-4b32-bc75-0009c0cc9a29_default" xlink:href="icui-20250930.xsd#icui_ClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_icui_ClassificationAxis_db756e46-6652-4b32-bc75-0009c0cc9a29" xlink:to="loc_icui_ClassificationDomain_db756e46-6652-4b32-bc75-0009c0cc9a29_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_ClassificationDomain_03260793-52ca-42b4-89a7-45273e539e42" xlink:href="icui-20250930.xsd#icui_ClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_icui_ClassificationAxis_db756e46-6652-4b32-bc75-0009c0cc9a29" xlink:to="loc_icui_ClassificationDomain_03260793-52ca-42b4-89a7-45273e539e42" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_CurrentMember_d51c6b1f-1e19-45cd-b389-b9c285afac9c" xlink:href="icui-20250930.xsd#icui_CurrentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_icui_ClassificationDomain_03260793-52ca-42b4-89a7-45273e539e42" xlink:to="loc_icui_CurrentMember_d51c6b1f-1e19-45cd-b389-b9c285afac9c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_NoncurrentMember_5cf4877f-0ee2-4ad5-8960-c42243c44524" xlink:href="icui-20250930.xsd#icui_NoncurrentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_icui_ClassificationDomain_03260793-52ca-42b4-89a7-45273e539e42" xlink:to="loc_icui_NoncurrentMember_5cf4877f-0ee2-4ad5-8960-c42243c44524" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignCurrencyContractAssetFairValueDisclosure_d405ea08-4e5e-4073-955b-6192dd8b7fb4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ForeignCurrencyContractAssetFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_de2420a2-89de-4ff2-a1bc-28815e271b69" xlink:to="loc_us-gaap_ForeignCurrencyContractAssetFairValueDisclosure_d405ea08-4e5e-4073-955b-6192dd8b7fb4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateDerivativeAssetsAtFairValue_1c9cad55-551c-4972-95e4-6bc98ddd900f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InterestRateDerivativeAssetsAtFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_de2420a2-89de-4ff2-a1bc-28815e271b69" xlink:to="loc_us-gaap_InterestRateDerivativeAssetsAtFairValue_1c9cad55-551c-4972-95e4-6bc98ddd900f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsFairValueDisclosure_1018a6df-6557-4230-9f6d-1ec8f9591e0e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AssetsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_de2420a2-89de-4ff2-a1bc-28815e271b69" xlink:to="loc_us-gaap_AssetsFairValueDisclosure_1018a6df-6557-4230-9f6d-1ec8f9591e0e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignCurrencyContractsLiabilityFairValueDisclosure_3b4c14dd-0cd6-4a49-afb8-1322dcc4c319" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ForeignCurrencyContractsLiabilityFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_de2420a2-89de-4ff2-a1bc-28815e271b69" xlink:to="loc_us-gaap_ForeignCurrencyContractsLiabilityFairValueDisclosure_3b4c14dd-0cd6-4a49-afb8-1322dcc4c319" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateDerivativeLiabilitiesAtFairValue_e49582c7-838d-4289-a17b-5c7053b25664" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InterestRateDerivativeLiabilitiesAtFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_de2420a2-89de-4ff2-a1bc-28815e271b69" xlink:to="loc_us-gaap_InterestRateDerivativeLiabilitiesAtFairValue_e49582c7-838d-4289-a17b-5c7053b25664" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialLiabilitiesFairValueDisclosure_f8d1f579-e376-4437-a94f-01b9766ddf9f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancialLiabilitiesFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_de2420a2-89de-4ff2-a1bc-28815e271b69" xlink:to="loc_us-gaap_FinancialLiabilitiesFairValueDisclosure_f8d1f579-e376-4437-a94f-01b9766ddf9f" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeAssetCurrentStatementOfFinancialPositionExtensibleEnumeration_74c052f0-a674-4ea3-950b-888ef2344ae3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeAssetCurrentStatementOfFinancialPositionExtensibleEnumeration"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_de2420a2-89de-4ff2-a1bc-28815e271b69" xlink:to="loc_us-gaap_DerivativeAssetCurrentStatementOfFinancialPositionExtensibleEnumeration_74c052f0-a674-4ea3-950b-888ef2344ae3" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeAssetNoncurrentStatementOfFinancialPositionExtensibleEnumeration_5dd9b5ea-7289-409b-b531-3c0ee7031b0e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeAssetNoncurrentStatementOfFinancialPositionExtensibleEnumeration"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_de2420a2-89de-4ff2-a1bc-28815e271b69" xlink:to="loc_us-gaap_DerivativeAssetNoncurrentStatementOfFinancialPositionExtensibleEnumeration_5dd9b5ea-7289-409b-b531-3c0ee7031b0e" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLiabilityCurrentStatementOfFinancialPositionExtensibleEnumeration_2050436e-90a9-46d0-b2f3-3015b66b5f75" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeLiabilityCurrentStatementOfFinancialPositionExtensibleEnumeration"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_de2420a2-89de-4ff2-a1bc-28815e271b69" xlink:to="loc_us-gaap_DerivativeLiabilityCurrentStatementOfFinancialPositionExtensibleEnumeration_2050436e-90a9-46d0-b2f3-3015b66b5f75" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLiabilityNoncurrentStatementOfFinancialPositionExtensibleEnumeration_a09d18c4-275c-43e3-ab42-cf9ca5d2eeec" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeLiabilityNoncurrentStatementOfFinancialPositionExtensibleEnumeration"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_de2420a2-89de-4ff2-a1bc-28815e271b69" xlink:to="loc_us-gaap_DerivativeLiabilityNoncurrentStatementOfFinancialPositionExtensibleEnumeration_a09d18c4-275c-43e3-ab42-cf9ca5d2eeec" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonfinancialLiabilitiesFairValueDisclosure_4e12e743-0e10-4735-8b5c-4dd7b494d9f2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NonfinancialLiabilitiesFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_de2420a2-89de-4ff2-a1bc-28815e271b69" xlink:to="loc_us-gaap_NonfinancialLiabilitiesFairValueDisclosure_4e12e743-0e10-4735-8b5c-4dd7b494d9f2" xlink:type="arc" order="10"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.icumed.com/role/InvestmentsEquityMethodandJointVenturesDetails" xlink:type="simple" xlink:href="icui-20250930.xsd#InvestmentsEquityMethodandJointVenturesDetails"/>
  <link:definitionLink xlink:role="http://www.icumed.com/role/InvestmentsEquityMethodandJointVenturesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_88f6ae7b-bec1-497f-a508-cc5127964f49" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfEquityMethodInvestmentsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_80636e19-ff82-4d09-9f99-b4687cad570f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfEquityMethodInvestmentsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_88f6ae7b-bec1-497f-a508-cc5127964f49" xlink:to="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_80636e19-ff82-4d09-9f99-b4687cad570f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeAxis_2c80b1ea-e1a2-4a5e-9df4-d4eaf4a8968d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_80636e19-ff82-4d09-9f99-b4687cad570f" xlink:to="loc_us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeAxis_2c80b1ea-e1a2-4a5e-9df4-d4eaf4a8968d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeDomain_2c80b1ea-e1a2-4a5e-9df4-d4eaf4a8968d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeAxis_2c80b1ea-e1a2-4a5e-9df4-d4eaf4a8968d" xlink:to="loc_us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeDomain_2c80b1ea-e1a2-4a5e-9df4-d4eaf4a8968d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeDomain_02bde2e2-9b64-41e3-b44b-5e2c11d639e5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeAxis_2c80b1ea-e1a2-4a5e-9df4-d4eaf4a8968d" xlink:to="loc_us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeDomain_02bde2e2-9b64-41e3-b44b-5e2c11d639e5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_UsGaap_OtsukaICUMedicalLLCMember_d5dbcfc8-cab6-469d-b5d0-81ebd8484a2a" xlink:href="icui-20250930.xsd#icui_UsGaap_OtsukaICUMedicalLLCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeDomain_02bde2e2-9b64-41e3-b44b-5e2c11d639e5" xlink:to="loc_icui_UsGaap_OtsukaICUMedicalLLCMember_d5dbcfc8-cab6-469d-b5d0-81ebd8484a2a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_UsGaap_OtherInvestmentsMemberMember_33c6ee42-f93d-4b63-a17c-811a82a9a451" xlink:href="icui-20250930.xsd#icui_UsGaap_OtherInvestmentsMemberMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeDomain_02bde2e2-9b64-41e3-b44b-5e2c11d639e5" xlink:to="loc_icui_UsGaap_OtherInvestmentsMemberMember_33c6ee42-f93d-4b63-a17c-811a82a9a451" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_JVandVIMember_877eb8a5-5228-4aa9-b934-63d7afb6b22e" xlink:href="icui-20250930.xsd#icui_JVandVIMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeDomain_02bde2e2-9b64-41e3-b44b-5e2c11d639e5" xlink:to="loc_icui_JVandVIMember_877eb8a5-5228-4aa9-b934-63d7afb6b22e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_UsGaap_EquityMethodInvestmentNonconsolidatedInvesteeNameAxisAxis_1ca2f4de-b877-4af5-a6f0-22df31d6f8c1" xlink:href="icui-20250930.xsd#icui_UsGaap_EquityMethodInvestmentNonconsolidatedInvesteeNameAxisAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_80636e19-ff82-4d09-9f99-b4687cad570f" xlink:to="loc_icui_UsGaap_EquityMethodInvestmentNonconsolidatedInvesteeNameAxisAxis_1ca2f4de-b877-4af5-a6f0-22df31d6f8c1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_UsGaap_EquityMethodInvestmentNonconsolidatedInvesteeNameAxisDomain_1ca2f4de-b877-4af5-a6f0-22df31d6f8c1_default" xlink:href="icui-20250930.xsd#icui_UsGaap_EquityMethodInvestmentNonconsolidatedInvesteeNameAxisDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_icui_UsGaap_EquityMethodInvestmentNonconsolidatedInvesteeNameAxisAxis_1ca2f4de-b877-4af5-a6f0-22df31d6f8c1" xlink:to="loc_icui_UsGaap_EquityMethodInvestmentNonconsolidatedInvesteeNameAxisDomain_1ca2f4de-b877-4af5-a6f0-22df31d6f8c1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_UsGaap_EquityMethodInvestmentNonconsolidatedInvesteeNameAxisDomain_6d7b5234-6850-4732-8409-e8473910e0f4" xlink:href="icui-20250930.xsd#icui_UsGaap_EquityMethodInvestmentNonconsolidatedInvesteeNameAxisDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_icui_UsGaap_EquityMethodInvestmentNonconsolidatedInvesteeNameAxisAxis_1ca2f4de-b877-4af5-a6f0-22df31d6f8c1" xlink:to="loc_icui_UsGaap_EquityMethodInvestmentNonconsolidatedInvesteeNameAxisDomain_6d7b5234-6850-4732-8409-e8473910e0f4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_UsGaap_OtsukaICUMedicalLLCMember_996b7485-981e-4541-909f-6f3811917477" xlink:href="icui-20250930.xsd#icui_UsGaap_OtsukaICUMedicalLLCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_icui_UsGaap_EquityMethodInvestmentNonconsolidatedInvesteeNameAxisDomain_6d7b5234-6850-4732-8409-e8473910e0f4" xlink:to="loc_icui_UsGaap_OtsukaICUMedicalLLCMember_996b7485-981e-4541-909f-6f3811917477" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_UsGaap_OtherInvestmentsMemberMember_e29803ac-719b-4866-ab3a-1b47f40fc8a2" xlink:href="icui-20250930.xsd#icui_UsGaap_OtherInvestmentsMemberMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_icui_UsGaap_EquityMethodInvestmentNonconsolidatedInvesteeNameAxisDomain_6d7b5234-6850-4732-8409-e8473910e0f4" xlink:to="loc_icui_UsGaap_OtherInvestmentsMemberMember_e29803ac-719b-4866-ab3a-1b47f40fc8a2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_383d5bba-5c55-426e-ab3a-2f5f2d9bb586" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_80636e19-ff82-4d09-9f99-b4687cad570f" xlink:to="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_383d5bba-5c55-426e-ab3a-2f5f2d9bb586" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_383d5bba-5c55-426e-ab3a-2f5f2d9bb586_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_EquityMethodInvesteeNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_383d5bba-5c55-426e-ab3a-2f5f2d9bb586" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_383d5bba-5c55-426e-ab3a-2f5f2d9bb586_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_680f5856-ef61-4bc0-85ed-1a09a8f25414" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_EquityMethodInvesteeNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_383d5bba-5c55-426e-ab3a-2f5f2d9bb586" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_680f5856-ef61-4bc0-85ed-1a09a8f25414" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_UsGaap_OtsukaICUMedicalLLCMember_e360fd5f-d9a8-400c-9194-ebf76f6c2802" xlink:href="icui-20250930.xsd#icui_UsGaap_OtsukaICUMedicalLLCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_EquityMethodInvesteeNameDomain_680f5856-ef61-4bc0-85ed-1a09a8f25414" xlink:to="loc_icui_UsGaap_OtsukaICUMedicalLLCMember_e360fd5f-d9a8-400c-9194-ebf76f6c2802" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_UsGaap_OtherInvestmentsMemberMember_d930c029-6077-417c-94db-dd56caaae1b1" xlink:href="icui-20250930.xsd#icui_UsGaap_OtherInvestmentsMemberMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_EquityMethodInvesteeNameDomain_680f5856-ef61-4bc0-85ed-1a09a8f25414" xlink:to="loc_icui_UsGaap_OtherInvestmentsMemberMember_d930c029-6077-417c-94db-dd56caaae1b1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_JVandVIMember_921ca012-c697-4225-8c15-76d51a735882" xlink:href="icui-20250930.xsd#icui_JVandVIMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_EquityMethodInvesteeNameDomain_680f5856-ef61-4bc0-85ed-1a09a8f25414" xlink:to="loc_icui_JVandVIMember_921ca012-c697-4225-8c15-76d51a735882" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityMethodInvestmentOwnershipPercentage_d2b20ad7-c2fd-4822-9a28-7f3f5b53eab9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityMethodInvestmentOwnershipPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_88f6ae7b-bec1-497f-a508-cc5127964f49" xlink:to="loc_us-gaap_EquityMethodInvestmentOwnershipPercentage_d2b20ad7-c2fd-4822-9a28-7f3f5b53eab9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityMethodInvestmentAggregateCost_b6e07a07-d5a4-4e0c-b8de-fa3a63146d9d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityMethodInvestmentAggregateCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_88f6ae7b-bec1-497f-a508-cc5127964f49" xlink:to="loc_us-gaap_EquityMethodInvestmentAggregateCost_b6e07a07-d5a4-4e0c-b8de-fa3a63146d9d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityMethodInvestments_779ff455-8808-4792-a079-332d94dd3fd3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityMethodInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_88f6ae7b-bec1-497f-a508-cc5127964f49" xlink:to="loc_us-gaap_EquityMethodInvestments_779ff455-8808-4792-a079-332d94dd3fd3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromEquityMethodInvestments_c66fffef-c8a1-46d7-83a4-6d0674780e32" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeLossFromEquityMethodInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_88f6ae7b-bec1-497f-a508-cc5127964f49" xlink:to="loc_us-gaap_IncomeLossFromEquityMethodInvestments_c66fffef-c8a1-46d7-83a4-6d0674780e32" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransferToInvestments_8d7d528b-609e-4977-aff8-b4c27e87b0c0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TransferToInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_88f6ae7b-bec1-497f-a508-cc5127964f49" xlink:to="loc_us-gaap_TransferToInvestments_8d7d528b-609e-4977-aff8-b4c27e87b0c0" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.icumed.com/role/PrepaidsandOtherCurrentAssetsPrepaidsandOtherAssetsDetails" xlink:type="simple" xlink:href="icui-20250930.xsd#PrepaidsandOtherCurrentAssetsPrepaidsandOtherAssetsDetails"/>
  <link:definitionLink xlink:role="http://www.icumed.com/role/PrepaidsandOtherCurrentAssetsPrepaidsandOtherAssetsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLineItems_950be2c4-2d72-42fc-919f-228ac875549f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeTable_abbee1d0-82ed-4993-ae23-5f8fa9303654" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeLineItems_950be2c4-2d72-42fc-919f-228ac875549f" xlink:to="loc_us-gaap_DerivativeTable_abbee1d0-82ed-4993-ae23-5f8fa9303654" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationAxis_7c4c7f64-7bed-4912-ba7f-adb58f01ec18" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BalanceSheetLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_abbee1d0-82ed-4993-ae23-5f8fa9303654" xlink:to="loc_us-gaap_BalanceSheetLocationAxis_7c4c7f64-7bed-4912-ba7f-adb58f01ec18" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationDomain_7c4c7f64-7bed-4912-ba7f-adb58f01ec18_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BalanceSheetLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BalanceSheetLocationAxis_7c4c7f64-7bed-4912-ba7f-adb58f01ec18" xlink:to="loc_us-gaap_BalanceSheetLocationDomain_7c4c7f64-7bed-4912-ba7f-adb58f01ec18_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationDomain_96f7a86e-a2c8-4bd7-86eb-cfc78919d339" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BalanceSheetLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BalanceSheetLocationAxis_7c4c7f64-7bed-4912-ba7f-adb58f01ec18" xlink:to="loc_us-gaap_BalanceSheetLocationDomain_96f7a86e-a2c8-4bd7-86eb-cfc78919d339" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PrepaidExpensesAndOtherCurrentAssetsMember_2a02a431-8f0a-4aff-b0be-297122344a1b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PrepaidExpensesAndOtherCurrentAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetLocationDomain_96f7a86e-a2c8-4bd7-86eb-cfc78919d339" xlink:to="loc_us-gaap_PrepaidExpensesAndOtherCurrentAssetsMember_2a02a431-8f0a-4aff-b0be-297122344a1b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateDerivativeAssetsAtFairValue_b5cf4d1a-95c8-40ae-9a27-2be133445ddd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InterestRateDerivativeAssetsAtFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_950be2c4-2d72-42fc-919f-228ac875549f" xlink:to="loc_us-gaap_InterestRateDerivativeAssetsAtFairValue_b5cf4d1a-95c8-40ae-9a27-2be133445ddd" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.icumed.com/role/GoodwillandIntangibleAssetsIntangiblesTableDetails" xlink:type="simple" xlink:href="icui-20250930.xsd#GoodwillandIntangibleAssetsIntangiblesTableDetails"/>
  <link:definitionLink xlink:role="http://www.icumed.com/role/GoodwillandIntangibleAssetsIntangiblesTableDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_96e70d79-52bc-4f04-9e47-f4f34b1d5469" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_cba2c08f-5ede-40c2-89ae-3aee59f2e21c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_96e70d79-52bc-4f04-9e47-f4f34b1d5469" xlink:to="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_cba2c08f-5ede-40c2-89ae-3aee59f2e21c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_26b02c73-1375-43a3-9ab1-13b29b534d10" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_cba2c08f-5ede-40c2-89ae-3aee59f2e21c" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_26b02c73-1375-43a3-9ab1-13b29b534d10" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_26b02c73-1375-43a3-9ab1-13b29b534d10_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_26b02c73-1375-43a3-9ab1-13b29b534d10" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_26b02c73-1375-43a3-9ab1-13b29b534d10_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_3628c7f7-8ac6-4c93-ac8f-64035b0e78e3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_26b02c73-1375-43a3-9ab1-13b29b534d10" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_3628c7f7-8ac6-4c93-ac8f-64035b0e78e3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PatentsMember_288aefd4-f958-40d6-a1ed-2f06d03b1b0e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PatentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_3628c7f7-8ac6-4c93-ac8f-64035b0e78e3" xlink:to="loc_us-gaap_PatentsMember_288aefd4-f958-40d6-a1ed-2f06d03b1b0e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerContractsMember_94bb04e2-88d3-45fa-9d23-e34056ef0c2a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CustomerContractsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_3628c7f7-8ac6-4c93-ac8f-64035b0e78e3" xlink:to="loc_us-gaap_CustomerContractsMember_94bb04e2-88d3-45fa-9d23-e34056ef0c2a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerRelatedIntangibleAssetsMember_45a7267c-fa4d-45fc-a00a-abd0a7ec7d90" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CustomerRelatedIntangibleAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_3628c7f7-8ac6-4c93-ac8f-64035b0e78e3" xlink:to="loc_us-gaap_CustomerRelatedIntangibleAssetsMember_45a7267c-fa4d-45fc-a00a-abd0a7ec7d90" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TrademarksMember_6551d6ec-6163-45d1-af97-387d3a5a3054" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TrademarksMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_3628c7f7-8ac6-4c93-ac8f-64035b0e78e3" xlink:to="loc_us-gaap_TrademarksMember_6551d6ec-6163-45d1-af97-387d3a5a3054" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TradeNamesMember_cb3b7803-40ef-4e1c-bc82-5c159cb7a29d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TradeNamesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_3628c7f7-8ac6-4c93-ac8f-64035b0e78e3" xlink:to="loc_us-gaap_TradeNamesMember_cb3b7803-40ef-4e1c-bc82-5c159cb7a29d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DevelopedTechnologyRightsMember_37ee7bff-1abf-4ea7-80b1-2d08c3a48813" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DevelopedTechnologyRightsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_3628c7f7-8ac6-4c93-ac8f-64035b0e78e3" xlink:to="loc_us-gaap_DevelopedTechnologyRightsMember_37ee7bff-1abf-4ea7-80b1-2d08c3a48813" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NoncompeteAgreementsMember_6d04824e-75ac-4e7e-b981-434019f6abe0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NoncompeteAgreementsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_3628c7f7-8ac6-4c93-ac8f-64035b0e78e3" xlink:to="loc_us-gaap_NoncompeteAgreementsMember_6d04824e-75ac-4e7e-b981-434019f6abe0" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_8daeac91-8f8b-40a2-b058-169f885ff6f2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_96e70d79-52bc-4f04-9e47-f4f34b1d5469" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_8daeac91-8f8b-40a2-b058-169f885ff6f2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsGross_6380544b-1a24-4bb3-bbb1-9074331ce924" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_96e70d79-52bc-4f04-9e47-f4f34b1d5469" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsGross_6380544b-1a24-4bb3-bbb1-9074331ce924" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_4ea94e4d-67ea-4c6b-bebd-0f2077b20eaa" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_96e70d79-52bc-4f04-9e47-f4f34b1d5469" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_4ea94e4d-67ea-4c6b-bebd-0f2077b20eaa" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsNet_0e227a7b-cfd0-4d13-b357-dc171bbece81" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_96e70d79-52bc-4f04-9e47-f4f34b1d5469" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsNet_0e227a7b-cfd0-4d13-b357-dc171bbece81" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill_e0a8c375-db4b-43e3-b797-d473d38891f0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_96e70d79-52bc-4f04-9e47-f4f34b1d5469" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill_e0a8c375-db4b-43e3-b797-d473d38891f0" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IntangibleAssetsGrossExcludingGoodwill_270e48f4-8c28-4cb6-9a42-a78710a6b6cf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IntangibleAssetsGrossExcludingGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_96e70d79-52bc-4f04-9e47-f4f34b1d5469" xlink:to="loc_us-gaap_IntangibleAssetsGrossExcludingGoodwill_270e48f4-8c28-4cb6-9a42-a78710a6b6cf" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IntangibleAssetsNetExcludingGoodwill_a39c03a8-40ea-4101-91d0-b9d640b5fab8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IntangibleAssetsNetExcludingGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_96e70d79-52bc-4f04-9e47-f4f34b1d5469" xlink:to="loc_us-gaap_IntangibleAssetsNetExcludingGoodwill_a39c03a8-40ea-4101-91d0-b9d640b5fab8" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.icumed.com/role/IncomeTaxesEffectivetaxrateDetails" xlink:type="simple" xlink:href="icui-20250930.xsd#IncomeTaxesEffectivetaxrateDetails"/>
  <link:definitionLink xlink:role="http://www.icumed.com/role/IncomeTaxesEffectivetaxrateDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionContingentConsiderationLineItems_66c5d7c0-e8b0-496e-8eaf-f5511efe8658" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionContingentConsiderationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionContingentConsiderationTable_b564e7fe-c8dd-49ce-8537-ad8d9dd671e5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionContingentConsiderationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionContingentConsiderationLineItems_66c5d7c0-e8b0-496e-8eaf-f5511efe8658" xlink:to="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionContingentConsiderationTable_b564e7fe-c8dd-49ce-8537-ad8d9dd671e5" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_e2303710-5265-47a5-9c56-b9d40297bf40" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionContingentConsiderationTable_b564e7fe-c8dd-49ce-8537-ad8d9dd671e5" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_e2303710-5265-47a5-9c56-b9d40297bf40" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_e2303710-5265-47a5-9c56-b9d40297bf40_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_e2303710-5265-47a5-9c56-b9d40297bf40" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_e2303710-5265-47a5-9c56-b9d40297bf40_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_b0e2b9e9-6ffa-463b-9920-b4ee97cc5056" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_e2303710-5265-47a5-9c56-b9d40297bf40" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_b0e2b9e9-6ffa-463b-9920-b4ee97cc5056" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_SmithsMedicalMember_e6546744-fd23-4cb7-b1a9-d475476310e7" xlink:href="icui-20250930.xsd#icui_SmithsMedicalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_b0e2b9e9-6ffa-463b-9920-b4ee97cc5056" xlink:to="loc_icui_SmithsMedicalMember_e6546744-fd23-4cb7-b1a9-d475476310e7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationContingentConsiderationArrangementsChangeInAmountOfContingentConsiderationLiability1_bc8587dd-e427-4a93-8283-4a090363b0c3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationContingentConsiderationArrangementsChangeInAmountOfContingentConsiderationLiability1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionContingentConsiderationLineItems_66c5d7c0-e8b0-496e-8eaf-f5511efe8658" xlink:to="loc_us-gaap_BusinessCombinationContingentConsiderationArrangementsChangeInAmountOfContingentConsiderationLiability1_bc8587dd-e427-4a93-8283-4a090363b0c3" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.icumed.com/role/LongTermObligationsDetails" xlink:type="simple" xlink:href="icui-20250930.xsd#LongTermObligationsDetails"/>
  <link:definitionLink xlink:role="http://www.icumed.com/role/LongTermObligationsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_4716f797-75f6-410e-a304-111fdda01047" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_59892e71-7622-47b4-a0be-31c34966cead" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_4716f797-75f6-410e-a304-111fdda01047" xlink:to="loc_us-gaap_DebtInstrumentTable_59892e71-7622-47b4-a0be-31c34966cead" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_c9e62b2e-c274-45f3-942e-ef5ac0041819" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_59892e71-7622-47b4-a0be-31c34966cead" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_c9e62b2e-c274-45f3-942e-ef5ac0041819" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_c9e62b2e-c274-45f3-942e-ef5ac0041819_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_c9e62b2e-c274-45f3-942e-ef5ac0041819" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_c9e62b2e-c274-45f3-942e-ef5ac0041819_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_7674f752-fe3e-4749-b75a-32d1036ca77d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_c9e62b2e-c274-45f3-942e-ef5ac0041819" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_7674f752-fe3e-4749-b75a-32d1036ca77d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevolvingCreditFacilityMember_205a3598-fa2f-451e-8b99-c376787087bc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_7674f752-fe3e-4749-b75a-32d1036ca77d" xlink:to="loc_us-gaap_RevolvingCreditFacilityMember_205a3598-fa2f-451e-8b99-c376787087bc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_TermLoanAxis_eee46a5c-2dcb-4fc2-bcaa-1faea6664e06" xlink:href="icui-20250930.xsd#icui_TermLoanAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_59892e71-7622-47b4-a0be-31c34966cead" xlink:to="loc_icui_TermLoanAxis_eee46a5c-2dcb-4fc2-bcaa-1faea6664e06" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_TermLoanDomain_eee46a5c-2dcb-4fc2-bcaa-1faea6664e06_default" xlink:href="icui-20250930.xsd#icui_TermLoanDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_icui_TermLoanAxis_eee46a5c-2dcb-4fc2-bcaa-1faea6664e06" xlink:to="loc_icui_TermLoanDomain_eee46a5c-2dcb-4fc2-bcaa-1faea6664e06_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_TermLoanDomain_3ae4edd3-d807-49d4-971d-be0dde870bc0" xlink:href="icui-20250930.xsd#icui_TermLoanDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_icui_TermLoanAxis_eee46a5c-2dcb-4fc2-bcaa-1faea6664e06" xlink:to="loc_icui_TermLoanDomain_3ae4edd3-d807-49d4-971d-be0dde870bc0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_TermLoanAMember_0e8f3c3e-697c-4208-bea5-229b4094013d" xlink:href="icui-20250930.xsd#icui_TermLoanAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_icui_TermLoanDomain_3ae4edd3-d807-49d4-971d-be0dde870bc0" xlink:to="loc_icui_TermLoanAMember_0e8f3c3e-697c-4208-bea5-229b4094013d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_TermLoanBMember_3170fd5d-0adb-4bf6-b1c5-aa5f76582e6a" xlink:href="icui-20250930.xsd#icui_TermLoanBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_icui_TermLoanDomain_3ae4edd3-d807-49d4-971d-be0dde870bc0" xlink:to="loc_icui_TermLoanBMember_3170fd5d-0adb-4bf6-b1c5-aa5f76582e6a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_TotalSeniorSecuredCreditFacility_c0271745-50b6-4d96-b06e-25e825b06d6d" xlink:href="icui-20250930.xsd#icui_TotalSeniorSecuredCreditFacility"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_4716f797-75f6-410e-a304-111fdda01047" xlink:to="loc_icui_TotalSeniorSecuredCreditFacility_c0271745-50b6-4d96-b06e-25e825b06d6d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromIssuanceOfDebt_04edb660-e1b3-4e26-9f53-d84a8babc219" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ProceedsFromIssuanceOfDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_4716f797-75f6-410e-a304-111fdda01047" xlink:to="loc_us-gaap_ProceedsFromIssuanceOfDebt_04edb660-e1b3-4e26-9f53-d84a8babc219" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentCarryingAmount_b129c78b-63bd-4ba5-8df0-dbffbaab97e4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentCarryingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_4716f797-75f6-410e-a304-111fdda01047" xlink:to="loc_us-gaap_DebtInstrumentCarryingAmount_b129c78b-63bd-4ba5-8df0-dbffbaab97e4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_RevolverSubLimits_e911f844-14a3-4dbd-8533-1bed4687ed57" xlink:href="icui-20250930.xsd#icui_RevolverSubLimits"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_4716f797-75f6-410e-a304-111fdda01047" xlink:to="loc_icui_RevolverSubLimits_e911f844-14a3-4dbd-8533-1bed4687ed57" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredFinanceCostsGross_21429d97-01ac-4caf-9e61-1262e9aa243d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DeferredFinanceCostsGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_4716f797-75f6-410e-a304-111fdda01047" xlink:to="loc_us-gaap_DeferredFinanceCostsGross_21429d97-01ac-4caf-9e61-1262e9aa243d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebt_f37f6a25-d755-4449-bc93-cdf1faaf842f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_4716f797-75f6-410e-a304-111fdda01047" xlink:to="loc_us-gaap_LongTermDebt_f37f6a25-d755-4449-bc93-cdf1faaf842f" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentMaturityDate_1161a9d3-937a-45a2-9198-cd2788fc4086" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentMaturityDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_4716f797-75f6-410e-a304-111fdda01047" xlink:to="loc_us-gaap_DebtInstrumentMaturityDate_1161a9d3-937a-45a2-9198-cd2788fc4086" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_LeverageRatioCalculationCeilingSubtractedAmount_d7145c8e-0cba-47f9-bd58-e761dc51647b" xlink:href="icui-20250930.xsd#icui_LeverageRatioCalculationCeilingSubtractedAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_4716f797-75f6-410e-a304-111fdda01047" xlink:to="loc_icui_LeverageRatioCalculationCeilingSubtractedAmount_d7145c8e-0cba-47f9-bd58-e761dc51647b" xlink:type="arc" order="7"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.icumed.com/role/LongTermObligationsInterestRateTermsDetails" xlink:type="simple" xlink:href="icui-20250930.xsd#LongTermObligationsInterestRateTermsDetails"/>
  <link:definitionLink xlink:role="http://www.icumed.com/role/LongTermObligationsInterestRateTermsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_icui_ApplicableMarginBasedOnLeverageRatioLineItems_75c73eb2-9976-4441-913d-cf3ad36f9ae5" xlink:href="icui-20250930.xsd#icui_ApplicableMarginBasedOnLeverageRatioLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_ApplicableMarginBasedOnLeverageRatioTable_c90a3209-f507-4097-974a-ca88622f8d0f" xlink:href="icui-20250930.xsd#icui_ApplicableMarginBasedOnLeverageRatioTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_icui_ApplicableMarginBasedOnLeverageRatioLineItems_75c73eb2-9976-4441-913d-cf3ad36f9ae5" xlink:to="loc_icui_ApplicableMarginBasedOnLeverageRatioTable_c90a3209-f507-4097-974a-ca88622f8d0f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_TermLoanAxis_6ad3350e-2d57-4b8c-b6c7-dfe365bb3aad" xlink:href="icui-20250930.xsd#icui_TermLoanAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_icui_ApplicableMarginBasedOnLeverageRatioTable_c90a3209-f507-4097-974a-ca88622f8d0f" xlink:to="loc_icui_TermLoanAxis_6ad3350e-2d57-4b8c-b6c7-dfe365bb3aad" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_TermLoanDomain_6ad3350e-2d57-4b8c-b6c7-dfe365bb3aad_default" xlink:href="icui-20250930.xsd#icui_TermLoanDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_icui_TermLoanAxis_6ad3350e-2d57-4b8c-b6c7-dfe365bb3aad" xlink:to="loc_icui_TermLoanDomain_6ad3350e-2d57-4b8c-b6c7-dfe365bb3aad_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_TermLoanDomain_0d3fff97-fc71-462c-9117-7e958a2b53f6" xlink:href="icui-20250930.xsd#icui_TermLoanDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_icui_TermLoanAxis_6ad3350e-2d57-4b8c-b6c7-dfe365bb3aad" xlink:to="loc_icui_TermLoanDomain_0d3fff97-fc71-462c-9117-7e958a2b53f6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_TermLoanAMember_1343c00a-6d2f-4b3a-86c0-34174ec7b1cf" xlink:href="icui-20250930.xsd#icui_TermLoanAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_icui_TermLoanDomain_0d3fff97-fc71-462c-9117-7e958a2b53f6" xlink:to="loc_icui_TermLoanAMember_1343c00a-6d2f-4b3a-86c0-34174ec7b1cf" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_TermLoanBMember_219df9ce-83ef-4ab4-89b4-89767dae9fbc" xlink:href="icui-20250930.xsd#icui_TermLoanBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_icui_TermLoanDomain_0d3fff97-fc71-462c-9117-7e958a2b53f6" xlink:to="loc_icui_TermLoanBMember_219df9ce-83ef-4ab4-89b4-89767dae9fbc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_LeverageRatioLevelAxis_90c1b350-69a5-4598-b5c7-c629d5c790c1" xlink:href="icui-20250930.xsd#icui_LeverageRatioLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_icui_ApplicableMarginBasedOnLeverageRatioTable_c90a3209-f507-4097-974a-ca88622f8d0f" xlink:to="loc_icui_LeverageRatioLevelAxis_90c1b350-69a5-4598-b5c7-c629d5c790c1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_LeverageRatioLevelDomain_90c1b350-69a5-4598-b5c7-c629d5c790c1_default" xlink:href="icui-20250930.xsd#icui_LeverageRatioLevelDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_icui_LeverageRatioLevelAxis_90c1b350-69a5-4598-b5c7-c629d5c790c1" xlink:to="loc_icui_LeverageRatioLevelDomain_90c1b350-69a5-4598-b5c7-c629d5c790c1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_LeverageRatioLevelDomain_b5fa11a9-5e87-45ab-bc58-383ca09d4d75" xlink:href="icui-20250930.xsd#icui_LeverageRatioLevelDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_icui_LeverageRatioLevelAxis_90c1b350-69a5-4598-b5c7-c629d5c790c1" xlink:to="loc_icui_LeverageRatioLevelDomain_b5fa11a9-5e87-45ab-bc58-383ca09d4d75" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_Greaterthan400to100Member_67a8d684-2bc1-4f0e-9dd5-7246a2f39772" xlink:href="icui-20250930.xsd#icui_Greaterthan400to100Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_icui_LeverageRatioLevelDomain_b5fa11a9-5e87-45ab-bc58-383ca09d4d75" xlink:to="loc_icui_Greaterthan400to100Member_67a8d684-2bc1-4f0e-9dd5-7246a2f39772" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_LessThanOrEqualTo400To100ButGreaterThan300To100Member_c334ed55-c1a6-45d2-bcdb-181f02ace502" xlink:href="icui-20250930.xsd#icui_LessThanOrEqualTo400To100ButGreaterThan300To100Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_icui_LeverageRatioLevelDomain_b5fa11a9-5e87-45ab-bc58-383ca09d4d75" xlink:to="loc_icui_LessThanOrEqualTo400To100ButGreaterThan300To100Member_c334ed55-c1a6-45d2-bcdb-181f02ace502" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_LessThanOrEqual300To100ButGreaterThan250to100Member_859d1fd3-07fa-4ed4-8055-95b6ed21e3ac" xlink:href="icui-20250930.xsd#icui_LessThanOrEqual300To100ButGreaterThan250to100Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_icui_LeverageRatioLevelDomain_b5fa11a9-5e87-45ab-bc58-383ca09d4d75" xlink:to="loc_icui_LessThanOrEqual300To100ButGreaterThan250to100Member_859d1fd3-07fa-4ed4-8055-95b6ed21e3ac" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_LessThanOrEqualTo250To100ButGreaterThan200To100Member_704e077c-aa71-4fc3-8b65-8130a48937de" xlink:href="icui-20250930.xsd#icui_LessThanOrEqualTo250To100ButGreaterThan200To100Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_icui_LeverageRatioLevelDomain_b5fa11a9-5e87-45ab-bc58-383ca09d4d75" xlink:to="loc_icui_LessThanOrEqualTo250To100ButGreaterThan200To100Member_704e077c-aa71-4fc3-8b65-8130a48937de" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_LessThanOrEqualTo200To100Member_6eee6473-e417-4a77-841a-4e0c4579a1c5" xlink:href="icui-20250930.xsd#icui_LessThanOrEqualTo200To100Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_icui_LeverageRatioLevelDomain_b5fa11a9-5e87-45ab-bc58-383ca09d4d75" xlink:to="loc_icui_LessThanOrEqualTo200To100Member_6eee6473-e417-4a77-841a-4e0c4579a1c5" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_GreaterThan275To100Member_a5b4faa0-567f-476a-9c2d-ad628d74adbf" xlink:href="icui-20250930.xsd#icui_GreaterThan275To100Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_icui_LeverageRatioLevelDomain_b5fa11a9-5e87-45ab-bc58-383ca09d4d75" xlink:to="loc_icui_GreaterThan275To100Member_a5b4faa0-567f-476a-9c2d-ad628d74adbf" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_LessThan275To100Member_46669897-5175-4085-8e0f-863d373a888c" xlink:href="icui-20250930.xsd#icui_LessThan275To100Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_icui_LeverageRatioLevelDomain_b5fa11a9-5e87-45ab-bc58-383ca09d4d75" xlink:to="loc_icui_LessThan275To100Member_46669897-5175-4085-8e0f-863d373a888c" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_774c4900-5649-4ff3-8ce8-ada3a701f693" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_icui_ApplicableMarginBasedOnLeverageRatioTable_c90a3209-f507-4097-974a-ca88622f8d0f" xlink:to="loc_srt_RangeAxis_774c4900-5649-4ff3-8ce8-ada3a701f693" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_774c4900-5649-4ff3-8ce8-ada3a701f693_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_774c4900-5649-4ff3-8ce8-ada3a701f693" xlink:to="loc_srt_RangeMember_774c4900-5649-4ff3-8ce8-ada3a701f693_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_d75c55f6-31a8-4bc8-9ff6-ffc08652bd05" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_774c4900-5649-4ff3-8ce8-ada3a701f693" xlink:to="loc_srt_RangeMember_d75c55f6-31a8-4bc8-9ff6-ffc08652bd05" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_dd63c51d-de54-4dfd-987c-9b2de53c0641" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_d75c55f6-31a8-4bc8-9ff6-ffc08652bd05" xlink:to="loc_srt_MaximumMember_dd63c51d-de54-4dfd-987c-9b2de53c0641" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_eb6566da-46ba-4e4d-893c-811c5898488a" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_d75c55f6-31a8-4bc8-9ff6-ffc08652bd05" xlink:to="loc_srt_MinimumMember_eb6566da-46ba-4e4d-893c-811c5898488a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_ApplicableMarginBaseRateLoans_dbc44d4b-b624-41ef-a6eb-3e4bc4303016" xlink:href="icui-20250930.xsd#icui_ApplicableMarginBaseRateLoans"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_icui_ApplicableMarginBasedOnLeverageRatioLineItems_75c73eb2-9976-4441-913d-cf3ad36f9ae5" xlink:to="loc_icui_ApplicableMarginBaseRateLoans_dbc44d4b-b624-41ef-a6eb-3e4bc4303016" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_ApplicableMarginTermSOFRLoans_58e193ec-137f-475c-9580-31b475e7b333" xlink:href="icui-20250930.xsd#icui_ApplicableMarginTermSOFRLoans"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_icui_ApplicableMarginBasedOnLeverageRatioLineItems_75c73eb2-9976-4441-913d-cf3ad36f9ae5" xlink:to="loc_icui_ApplicableMarginTermSOFRLoans_58e193ec-137f-475c-9580-31b475e7b333" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityCommitmentFeePercentage_7fa5ea66-f7be-4cd6-91ea-f8d925003be0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCreditFacilityCommitmentFeePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_icui_ApplicableMarginBasedOnLeverageRatioLineItems_75c73eb2-9976-4441-913d-cf3ad36f9ae5" xlink:to="loc_us-gaap_LineOfCreditFacilityCommitmentFeePercentage_7fa5ea66-f7be-4cd6-91ea-f8d925003be0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_TermSOFRAdjustmentInterestRateAdjustmentTermSOFRLoans_c5962d51-26e5-479d-b4b9-f07e38c2ffdb" xlink:href="icui-20250930.xsd#icui_TermSOFRAdjustmentInterestRateAdjustmentTermSOFRLoans"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_icui_ApplicableMarginBasedOnLeverageRatioLineItems_75c73eb2-9976-4441-913d-cf3ad36f9ae5" xlink:to="loc_icui_TermSOFRAdjustmentInterestRateAdjustmentTermSOFRLoans_c5962d51-26e5-479d-b4b9-f07e38c2ffdb" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.icumed.com/role/LongTermObligationsTableDetails" xlink:type="simple" xlink:href="icui-20250930.xsd#LongTermObligationsTableDetails"/>
  <link:definitionLink xlink:role="http://www.icumed.com/role/LongTermObligationsTableDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_7cfb5a35-34bc-47eb-9f37-e39f854ea239" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_352053d5-bf2b-46bb-8c83-8335e2c28311" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_7cfb5a35-34bc-47eb-9f37-e39f854ea239" xlink:to="loc_us-gaap_DebtInstrumentTable_352053d5-bf2b-46bb-8c83-8335e2c28311" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_TermLoanAxis_0de6b90e-9583-43a3-88aa-cf8e5f53e5b7" xlink:href="icui-20250930.xsd#icui_TermLoanAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_352053d5-bf2b-46bb-8c83-8335e2c28311" xlink:to="loc_icui_TermLoanAxis_0de6b90e-9583-43a3-88aa-cf8e5f53e5b7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_TermLoanDomain_0de6b90e-9583-43a3-88aa-cf8e5f53e5b7_default" xlink:href="icui-20250930.xsd#icui_TermLoanDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_icui_TermLoanAxis_0de6b90e-9583-43a3-88aa-cf8e5f53e5b7" xlink:to="loc_icui_TermLoanDomain_0de6b90e-9583-43a3-88aa-cf8e5f53e5b7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_TermLoanDomain_cc9fa883-2938-48c5-9f50-6339d56aea21" xlink:href="icui-20250930.xsd#icui_TermLoanDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_icui_TermLoanAxis_0de6b90e-9583-43a3-88aa-cf8e5f53e5b7" xlink:to="loc_icui_TermLoanDomain_cc9fa883-2938-48c5-9f50-6339d56aea21" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_TermLoanAMember_5007e82a-898b-4c42-a8dd-beb927fbacc4" xlink:href="icui-20250930.xsd#icui_TermLoanAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_icui_TermLoanDomain_cc9fa883-2938-48c5-9f50-6339d56aea21" xlink:to="loc_icui_TermLoanAMember_5007e82a-898b-4c42-a8dd-beb927fbacc4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_TermLoanBMember_57a88bdb-bd6d-4d9a-afb0-f4ed11daa370" xlink:href="icui-20250930.xsd#icui_TermLoanBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_icui_TermLoanDomain_cc9fa883-2938-48c5-9f50-6339d56aea21" xlink:to="loc_icui_TermLoanBMember_57a88bdb-bd6d-4d9a-afb0-f4ed11daa370" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_e00282f4-7751-47c0-8cf6-ff5228af91e8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_352053d5-bf2b-46bb-8c83-8335e2c28311" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_e00282f4-7751-47c0-8cf6-ff5228af91e8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_e00282f4-7751-47c0-8cf6-ff5228af91e8_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_e00282f4-7751-47c0-8cf6-ff5228af91e8" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_e00282f4-7751-47c0-8cf6-ff5228af91e8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_0b893cad-dd78-41e7-bdbf-3742bf5f81bd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_e00282f4-7751-47c0-8cf6-ff5228af91e8" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_0b893cad-dd78-41e7-bdbf-3742bf5f81bd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevolvingCreditFacilityMember_7745d440-03dc-4ccc-ae15-8b236d277742" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_0b893cad-dd78-41e7-bdbf-3742bf5f81bd" xlink:to="loc_us-gaap_RevolvingCreditFacilityMember_7745d440-03dc-4ccc-ae15-8b236d277742" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentCarryingAmount_2f7a21e8-3ee4-45ef-bd80-bb3d04d15d4a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentCarryingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_7cfb5a35-34bc-47eb-9f37-e39f854ea239" xlink:to="loc_us-gaap_DebtInstrumentCarryingAmount_2f7a21e8-3ee4-45ef-bd80-bb3d04d15d4a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityFairValueOfAmountOutstanding_b38416b5-f993-4e14-b476-4ba446c71d1e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCreditFacilityFairValueOfAmountOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_7cfb5a35-34bc-47eb-9f37-e39f854ea239" xlink:to="loc_us-gaap_LineOfCreditFacilityFairValueOfAmountOutstanding_b38416b5-f993-4e14-b476-4ba446c71d1e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentUnamortizedDiscountPremiumAndDebtIssuanceCostsNet_58428e96-13e2-4d0d-9b3d-74d2f860f80c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentUnamortizedDiscountPremiumAndDebtIssuanceCostsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_7cfb5a35-34bc-47eb-9f37-e39f854ea239" xlink:to="loc_us-gaap_DebtInstrumentUnamortizedDiscountPremiumAndDebtIssuanceCostsNet_58428e96-13e2-4d0d-9b3d-74d2f860f80c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtLongtermAndShorttermCombinedAmount_0d17716d-e5ac-4159-be0c-3ffdb894ac93" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtLongtermAndShorttermCombinedAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_7cfb5a35-34bc-47eb-9f37-e39f854ea239" xlink:to="loc_us-gaap_DebtLongtermAndShorttermCombinedAmount_0d17716d-e5ac-4159-be0c-3ffdb894ac93" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtCurrent_e8cc7a8b-b748-4c1a-9221-2f62855bb799" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_7cfb5a35-34bc-47eb-9f37-e39f854ea239" xlink:to="loc_us-gaap_DebtCurrent_e8cc7a8b-b748-4c1a-9221-2f62855bb799" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtNoncurrent_7fa60369-b121-45d3-8f4f-199dfd0ae66b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongTermDebtNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_7cfb5a35-34bc-47eb-9f37-e39f854ea239" xlink:to="loc_us-gaap_LongTermDebtNoncurrent_7fa60369-b121-45d3-8f4f-199dfd0ae66b" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateDuringPeriod_ec430cb1-2b31-4f85-a2ab-450593dc1f5e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentInterestRateDuringPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_7cfb5a35-34bc-47eb-9f37-e39f854ea239" xlink:to="loc_us-gaap_DebtInstrumentInterestRateDuringPeriod_ec430cb1-2b31-4f85-a2ab-450593dc1f5e" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.icumed.com/role/CommitmentsandContingenciesContingencyDetails" xlink:type="simple" xlink:href="icui-20250930.xsd#CommitmentsandContingenciesContingencyDetails"/>
  <link:definitionLink xlink:role="http://www.icumed.com/role/CommitmentsandContingenciesContingencyDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionContingentConsiderationLineItems_9cc45303-adb7-4e03-9d15-f1c82b10b6e7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionContingentConsiderationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionContingentConsiderationTable_99a876f1-9db3-4a42-ad5a-0625f23eb044" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionContingentConsiderationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionContingentConsiderationLineItems_9cc45303-adb7-4e03-9d15-f1c82b10b6e7" xlink:to="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionContingentConsiderationTable_99a876f1-9db3-4a42-ad5a-0625f23eb044" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_7407b699-7116-4405-9785-d69bf1bc4710" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionContingentConsiderationTable_99a876f1-9db3-4a42-ad5a-0625f23eb044" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_7407b699-7116-4405-9785-d69bf1bc4710" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_7407b699-7116-4405-9785-d69bf1bc4710_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_7407b699-7116-4405-9785-d69bf1bc4710" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_7407b699-7116-4405-9785-d69bf1bc4710_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_d8cf5246-a9c9-4756-a72c-43aa0e4f4e3e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_7407b699-7116-4405-9785-d69bf1bc4710" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_d8cf5246-a9c9-4756-a72c-43aa0e4f4e3e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_SmithsMedicalMember_33776e93-c731-4457-8bc7-31571f9acb2e" xlink:href="icui-20250930.xsd#icui_SmithsMedicalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_d8cf5246-a9c9-4756-a72c-43aa0e4f4e3e" xlink:to="loc_icui_SmithsMedicalMember_33776e93-c731-4457-8bc7-31571f9acb2e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_ForeignInfusionSystemSupplierMember_3a6294d6-5041-44b1-a1b2-ff2521d44d02" xlink:href="icui-20250930.xsd#icui_ForeignInfusionSystemSupplierMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_d8cf5246-a9c9-4756-a72c-43aa0e4f4e3e" xlink:to="loc_icui_ForeignInfusionSystemSupplierMember_3a6294d6-5041-44b1-a1b2-ff2521d44d02" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_InternationalDistributorMember_78f7c189-0c3b-4b39-b89d-cf6aa362c5b4" xlink:href="icui-20250930.xsd#icui_InternationalDistributorMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_d8cf5246-a9c9-4756-a72c-43aa0e4f4e3e" xlink:to="loc_icui_InternationalDistributorMember_78f7c189-0c3b-4b39-b89d-cf6aa362c5b4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_Contingentconsiderationgross_57c3347d-d4cc-411a-a919-4babab4cd1d6" xlink:href="icui-20250930.xsd#icui_Contingentconsiderationgross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionContingentConsiderationLineItems_9cc45303-adb7-4e03-9d15-f1c82b10b6e7" xlink:to="loc_icui_Contingentconsiderationgross_57c3347d-d4cc-411a-a919-4babab4cd1d6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_ContingentConsiderationGrossST_3ff2f752-8bdc-47fb-a747-d15e8e2a724e" xlink:href="icui-20250930.xsd#icui_ContingentConsiderationGrossST"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionContingentConsiderationLineItems_9cc45303-adb7-4e03-9d15-f1c82b10b6e7" xlink:to="loc_icui_ContingentConsiderationGrossST_3ff2f752-8bdc-47fb-a747-d15e8e2a724e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_ContingentConsiderationGrossLT_3354e2d2-0601-4b9b-a87a-b24e3bc4362d" xlink:href="icui-20250930.xsd#icui_ContingentConsiderationGrossLT"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionContingentConsiderationLineItems_9cc45303-adb7-4e03-9d15-f1c82b10b6e7" xlink:to="loc_icui_ContingentConsiderationGrossLT_3354e2d2-0601-4b9b-a87a-b24e3bc4362d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProductLiabilityAccrualComponentAmount_9f56acbe-0787-4f73-b02d-c10ace426fed" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ProductLiabilityAccrualComponentAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionContingentConsiderationLineItems_9cc45303-adb7-4e03-9d15-f1c82b10b6e7" xlink:to="loc_us-gaap_ProductLiabilityAccrualComponentAmount_9f56acbe-0787-4f73-b02d-c10ace426fed" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.icumed.com/role/SubsequentEventsDetails" xlink:type="simple" xlink:href="icui-20250930.xsd#SubsequentEventsDetails"/>
  <link:definitionLink xlink:role="http://www.icumed.com/role/SubsequentEventsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventLineItems_09d85fb5-dcc6-40f4-8412-f1d14ed53897" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTable_c10bc15e-66ec-4f48-865f-d5da435e86e8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SubsequentEventLineItems_09d85fb5-dcc6-40f4-8412-f1d14ed53897" xlink:to="loc_us-gaap_SubsequentEventTable_c10bc15e-66ec-4f48-865f-d5da435e86e8" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_TermLoanAxis_49dd3274-d48a-4f59-accb-414b4c11ae10" xlink:href="icui-20250930.xsd#icui_TermLoanAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_c10bc15e-66ec-4f48-865f-d5da435e86e8" xlink:to="loc_icui_TermLoanAxis_49dd3274-d48a-4f59-accb-414b4c11ae10" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_TermLoanDomain_49dd3274-d48a-4f59-accb-414b4c11ae10_default" xlink:href="icui-20250930.xsd#icui_TermLoanDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_icui_TermLoanAxis_49dd3274-d48a-4f59-accb-414b4c11ae10" xlink:to="loc_icui_TermLoanDomain_49dd3274-d48a-4f59-accb-414b4c11ae10_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_TermLoanDomain_a3574031-71c2-4a12-ac57-0c11606cdcf9" xlink:href="icui-20250930.xsd#icui_TermLoanDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_icui_TermLoanAxis_49dd3274-d48a-4f59-accb-414b4c11ae10" xlink:to="loc_icui_TermLoanDomain_a3574031-71c2-4a12-ac57-0c11606cdcf9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_TermLoanAMember_dd00ca3a-b2f7-4fa0-97ab-7a51d96d9e0b" xlink:href="icui-20250930.xsd#icui_TermLoanAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_icui_TermLoanDomain_a3574031-71c2-4a12-ac57-0c11606cdcf9" xlink:to="loc_icui_TermLoanAMember_dd00ca3a-b2f7-4fa0-97ab-7a51d96d9e0b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_TermLoanA1Member_9c68c1de-caec-44b9-81e4-d36047246ebe" xlink:href="icui-20250930.xsd#icui_TermLoanA1Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_icui_TermLoanDomain_a3574031-71c2-4a12-ac57-0c11606cdcf9" xlink:to="loc_icui_TermLoanA1Member_9c68c1de-caec-44b9-81e4-d36047246ebe" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeAxis_d6ecfbdc-bd07-4c28-82a8-a1c552415fbd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_c10bc15e-66ec-4f48-865f-d5da435e86e8" xlink:to="loc_us-gaap_SubsequentEventTypeAxis_d6ecfbdc-bd07-4c28-82a8-a1c552415fbd" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_d6ecfbdc-bd07-4c28-82a8-a1c552415fbd_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_d6ecfbdc-bd07-4c28-82a8-a1c552415fbd" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_d6ecfbdc-bd07-4c28-82a8-a1c552415fbd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_331107a4-0003-414a-8a8a-43e837b2039e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_d6ecfbdc-bd07-4c28-82a8-a1c552415fbd" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_331107a4-0003-414a-8a8a-43e837b2039e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventMember_953c1f1b-898b-40e4-823e-c436c9b9b5a4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventTypeDomain_331107a4-0003-414a-8a8a-43e837b2039e" xlink:to="loc_us-gaap_SubsequentEventMember_953c1f1b-898b-40e4-823e-c436c9b9b5a4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_af834713-1cbd-4476-9b88-39e8a8b12e3e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_c10bc15e-66ec-4f48-865f-d5da435e86e8" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_af834713-1cbd-4476-9b88-39e8a8b12e3e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_af834713-1cbd-4476-9b88-39e8a8b12e3e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_af834713-1cbd-4476-9b88-39e8a8b12e3e" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_af834713-1cbd-4476-9b88-39e8a8b12e3e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_efced389-52ee-4f1b-9b08-d40d13c914a3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_af834713-1cbd-4476-9b88-39e8a8b12e3e" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_efced389-52ee-4f1b-9b08-d40d13c914a3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevolvingCreditFacilityMember_ec3181d6-6884-4f3f-b917-81bb9389a1a6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_efced389-52ee-4f1b-9b08-d40d13c914a3" xlink:to="loc_us-gaap_RevolvingCreditFacilityMember_ec3181d6-6884-4f3f-b917-81bb9389a1a6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_icui_UsGaap_NewRevolvingCreditFacilityMember_8c3eab04-92c4-4868-8804-a4dda650dc2b" xlink:href="icui-20250930.xsd#icui_UsGaap_NewRevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_efced389-52ee-4f1b-9b08-d40d13c914a3" xlink:to="loc_icui_UsGaap_NewRevolvingCreditFacilityMember_8c3eab04-92c4-4868-8804-a4dda650dc2b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentCarryingAmount_245d7682-b4e5-45ca-b993-5ec163e4838f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentCarryingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_09d85fb5-dcc6-40f4-8412-f1d14ed53897" xlink:to="loc_us-gaap_DebtInstrumentCarryingAmount_245d7682-b4e5-45ca-b993-5ec163e4838f" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://fasb.org/us-gaap/role/eedm/ExtensibleEnumerationLists" xlink:type="simple" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-roles-2025.xsd#eedm"/>
  <link:definitionLink xlink:role="http://fasb.org/us-gaap/role/eedm/ExtensibleEnumerationLists" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesCurrentAbstract" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LiabilitiesCurrentAbstract"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccruedLiabilitiesCurrent" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccruedLiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract" xlink:to="loc_us-gaap_AccruedLiabilitiesCurrent" xlink:type="arc" order="41"/>
  </link:definitionLink>
</link:linkbase>
