**1. Introduction**

210 Perioperative Considerations in Cardiac Surgery

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> Intravenous heparin remains main stem therapy during cardiac and vascular surgical procedures. Heparin therapy is often continued after surgery as part of prophylactic treatment (deep venous thrombosis) or bridging therapy (for atrial fibrillation, prosthetic valve(s) or Dacron grafts implanted in the heart) until INR levels reach therapeutic levels with warfarin therapy.

> Complications resulting from the use of heparin are relatively rare. Among the most common are bleeding initiated by excessive inhibition of thrombin and other clotting factors and thrombosis caused by inadequate anticoagulation. Heparin Induced Thrombocytopenia (HIT) is a rare but potentially life-threatening complication. The literature, which is describing HIT is still somewhat confusing since it uses a variety for terms for HIT. Type I HIT, sometimes called non-immune heparin-associated thrombocytopenia, is a benign process and presents as a mild thrombocytopenia with the platelet count rarely decreasing below 100.000/ml. Type I HIT develops early after heparin exposure, typically within 2-3 days. It probably results from a direct effect of heparin on platelets and occurs in about 10%–30% of patients receiving heparin (1).

> In contrast, and of greater clinical concern, is type II HIT - and immune mediated syndrome associated with platelet activation, increased thrombin production and thrombogenesis leading to thrombo-embolic complications.

> The following chapter will briefly discuss the epidemiology, pathogenesis and management options for ICU and cardiac surgical patients diagnosed with true HIT.
