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Patients in the Critical Care setting may develop HIT as a result of chronic pre-existing risk factors (malignancy, obesity, hypertension, diabetes or medications) or acquired factors secondary to their ICU stay (post-operative state, trauma, central lines or medications such as heparin).
Diagnosis of HIT:
- platelet count<150,000 or relative decrease of 50% or more from baseline
- documentation of antibodies binding platelet factor 4 and heparin, as well as a confirmation test
- typically occurs 5-14 days after initiation of heparin therapy
- can have a rapid (usually a result of previous exposure) or delayed onset
- thrombotic complications develop in 20-50 percent of patients
Treatment of HIT:
- Remove all sources of heparin (including heparin-bonded catheters)
- initiate a non-heparin anticoagulant
- Direct thrombin inhibitors:
- Lepirudin (cleared by kidney)
- Argatroban (cleared by liver)
- Bivalirudin (cleared by proteolysis 80% and kidney 20%)
- Other agents used include:
- Danaparoid (antifactor Xa activity - not available in North America)
- Fondaparinux (synthetic selective inhibitor of Xa)
References
Critical Care Med 2010 Vol. 38, No. 2 (Suppl.)