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.)