THROMBIN ACTIVATION IN CARDIAC SURGICAL PATIENTS RECEIVING PREOPERATIVE HEPARIN INFUSIONS

Abstract

Introduction: Patients on heparin infusions (H) have a diminished activated coagulation time (ACT) response to the heparin bolus given for cardiopulmonary bypass (CPB), [1] which may place them at risk for inadequate anticoagulation. The High Dose Thrombin Time (HiTT), a specific measure of heparin activity, may be useful for patients on heparin therapy. [2] We compared patients receiving (H) and not receiving (nH) heparin with respect to ACT, HiTT, and thrombin generation during CPB. Methods: With IRB approval, 65 consecutive patients undergoing elective CPB were studied. Using bovine heparin 300 U/kg, ACT>or=to400 sec was maintained. ACT, and HiTT were measured at multiple time points. Plasma levels of F1.2, thrombin-antithrombin III complex (TAT), and fibrin monomer were determined at baseline, 30 min into CPB and after protamine administration. Blood loss and transfusions were recorded. Patients were compared using ANOVA, and Mann Whitney-U test where appropriate. P<0.05 was considered significant. Results: ACT values differed significantly in H (dotted line, n=32) vs. nH (solid line, n=33) patients, (p<0.003). HiTT values did not significantly differ between groups (p=0.33). (Figure 1) The two groups did not differ in any marker of thrombin formation or activity. (n=20, see Figure 2) Neither CTD (722 +/- 520 ml vs. 724 +/- 311 ml) nor transfusion requirements differed between groups.Figure 1Figure 2Discussion: H patients often receive additional boluses of heparin to maintain ACT>480 sec. Our data suggest that thrombin formation and activity are not enhanced in patients receiving H therapy despite a diminished ACT response to heparin. The utility of ACT in patients receiving H therapy and the threshold values perceived as indicative of adequate anticoagulation for CPB are questioned. The use of HiTT is currently under investigation.