The influence of antithrombin substitution on heparin sensitivity and activation of hemostasis during coronary artery bypass graft surgery: a dose-finding study.

BACKGROUND: Cardiopulmonary bypass is associated with a high degree of hemostatic system activation. Supplementation of antithrombin (AT) may attenuate this activation and increase a patient's susceptibility to heparin. However, the appropriate dosage of AT has not been defined. We sought to determine the dosage of AT concentrate necessary to achieve >100% AT activity at the end of cardiac surgery and the influence of AT on heparin sensitivity. METHODS: Forty-one patients were included. Thirty consecutive patients undergoing primary coronary artery bypass graft surgery with cardiopulmonary bypass were assigned to 3 groups of increasing dosages of AT concentrate. Eleven additional patients served as controls. AT activity and molecular markers of thrombin generation were determined, and heparin sensitivity was calculated. RESULTS: A median amount of 36.5 U (19.0; 42.8), 47.0 U (41.3; 61.6), and 50.0 U (47.4; 66.6) AT concentrate/kilogram body weight in the low, medium, and high AT group, respectively, was administered. At the end of surgery, AT activity with substitution was 84% (77; 111), 110% (92; 120), and 104% (97; 120) (median [25th; 75th percentile]), respectively, compared with 63% (49; 79) in controls (P < 0.05 all substitution groups versus control). Heparin sensitivity increased from 1.29 (1.17; 1.66) s/U heparin/kg in the control group to 2.02 (1.43; 3.65), 2.56 (1.52; 3.64), 1.72 (1.24; 2.66) s/U heparin/kg in the groups with substitution (P < 0.05 all substitution groups versus control). Compared with preoperative values, AT activity decreased during the postoperative period in all patients with a nadir on postoperative day 3 (P < 0.05 compared with baseline except for the medium AT group). Corresponding to this decrease, an increase in prothrombin fragment 1+2 and D-dimer could be observed postoperatively. DISCUSSION: High dosages of AT were required to preserve physiologic AT activity during coronary artery bypass graft surgery and to significantly enhance heparin sensitivity, respectively. However, a significant decrease in AT activity, accompanied by high levels of thrombin generation, was encountered up to 5 days postoperatively.