Anticoagulation for cardiac surgery in patients receiving preoperative heparin: Use of the high-dose thrombin time

Patients receiving heparin infusions have an attenuated activated clotting time (ACT) response to heparin given for cardiopulmonary bypass (CPB). We c ompared patients receiving preoperative heparin (Group H) to those not rece iving heparin (REF group) with respect to ACT, high-dose thrombin time (HiT T), and markers of thrombin generation during CPB. Sixty-five consecutive p atients (33 Group H, 32 REF group) undergoing elective CPB were evaluated. ACT and HiTT were measured at multiple time points. Plasma levels of thromb in-antithrombin III complex and fibrin monomer were determined at baseline, during CPB, and after protamine administration. Transfusion requirements a nd postoperative blood loss were measured and compared. ACT values after he parinization increased less in Group H and were significantly lower than th ose in the REF group (P < 0.01). HiTT values did not differ significantly b etween the two groups. Blood loss and transfusion requirements were not sig nificantly different between the two groups. Plasma levels of thrombin-anti thrombin III complexes and fibrin monomer also did not differ between group s at any time, despite a lower ACT in Group H after heparinization and duri ng CPB. Our data suggest that thrombin formation and activity are not enhan ced in patients receiving heparin therapy, despite a diminished ACT respons e to heparin. The utility of ACT and the threshold values indicative of ade quate anticoagulation for CPB are relatively undefined in patients receivin g preoperative heparin. HiTT should be investigated as a safe and accurate monitor of anticoagulation for CPB in patients receiving preoperative hepar in therapy. Implications: The diminished activated clotting time response t o heparin, in patients receiving preoperative heparin therapy, poses diffic ulties when attempting to provide adequate anticoagulation for cardiopulmon ary bypass. Current data suggest that heparin resistance is not observed wh en high-dose thrombin time is used to monitor anticoagulation and that a lo wer activated clotting time value in these patients may be safe.