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)
