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Heparin associated thrombocytopenia is often seen, but "heparin-induced hypercoagulability" is infrequent. In the hypercoagulable state, IgG antibodies form against platelet-heparin complexes that are sequestered on platelets at platelet Fc receptors and on endothelial cells where they may cause serious vascular occlusive disease and thrombocytopenia. Recently, it has been recognized that warfarin accelerates this phenomenon by further decreasing proteins of the protein C pathways, thereby enhancing hypercoagulability. The treatment of heparin-induced hypercoagulability, including purpura fulminans, requires immediate discontinuance of heparin administration. Hirudin (leech anticoagulant) and argatroban (synthetic antithrombin) are approved by the Food and Drug Administration and are the recommended treatment. Other options include ancrod (snake venom with antifibrinolytic activity), danaparoid (heparin, chrondroitin, and dermatan), and plasmapheresis. Low molecular weight heparin (LMWH) is risky because of potential cross reactivity with heparin antibodies. HIT TYPE I
Non-immune
10-20% relative decrease in PLT count
Early onset (i.e. day 1 of treatment)
Spontaeous resolution despite heparin continuation
Asymptomatic
HIT TYPE II
Immune-mediated
>30% relative decrease in PLT count
Delayed onset (day 5 of treatment)
(could start earlier if prior sensitization)
persistant or brutal aggravation until cessation of heparin
Manifestations include thrombosis (venous & arterial)
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Hirudin Dosage
1. HIT & THROMBOSIS:
0.4 mg/kg IV bolus followed by 0.15 mg/kg/hr target PTT 1.5-2.5
2. HIT & CONCOMITANT THROMBOLYSIS:
0.2 mg/kg IV bolus followed by 0.10 mg/kg/hr target PTT 1.5-2.5
3. HIT & ISOLATED THROMBOCYTOPENIA:
No bolus, 0.1 mg/kg/hr target PTT 1.5-2.5
4. THROMBOSIS PROPHYLAXIS IN PTS WITH HISTORY OF HIT:
No bolus, 0.1 mg/kg/hr target PTT 1.5-2.0
5. RENAL DIALYSIS OR CWH IN ICU PTS:
0.005 mg/kg/hr target PTT 1.5-2.5
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