Response of Recombinant Antithrombin in Heparin Resistant Patients Undergoing Cardiac Surgery

Inclusion Criteria: * Patients undergoing cardiac surgery requiring cardiopulmonary bypass (CPB) * Heparin resistant according to this definition: initial activated clotting time (ACT) after an intravenous loading dose of heparin (300 u/kg) is less than 480 seconds Exclusion criteria: * current use of one or more of these medications: * warfarin (within 3 days of surgery); * streptokinase; * tissue plasminogen activator; * abciximab, * eptifibatide, * tirofiban or * clopidogrel. * known hypersensitivity to goat or goat milk proteins, * patients with pre-existing coagulopathy defined as a history of bleeding or laboratory bleeding disorder (e.g., von Willebrand disease, platelet disorder) and * patients receiving direct thrombin inhibitors