Intraoperative anticoagulation in cardiovascular surgery.

The optimal heparin dose to prevent intraoperative thrombosis or excessive bleeding during the occlusive phase of cardiovascular operations has not been determined. Therefore, we studied the kinetics of heparin effect in 28 patient undergoing peripheral vascular and cardiac operations. The activated clotting time (ACT) was measured in seconds by an electronic clot timer. The maximum ACT after initial heparin administration, the time to reach maximum ACT, and the half-time of heparin effect (t1/2) were determined. The anticoagulant effect of a given dose of heparin varies greatly among patients. No correlation was found between the t1/2 and the dosage of heparin administered. Despite higher doses of heparin administered to cardiac patients, the t1/2 in cardiac and vascular patients was not significantly different. Four patients received the same dose of heparin preoperatively and intraoperatively in an effort to predict the intraoperative effect. The times to maximum effect were the same but t1/2 intraoperatively was longer. These results indicate: (1) maximum heparin effect occurs later than previously believed and is different for cardiac and peripheral vascular patients; (2) the recommendation to give more heparin based on the 5-minute ACT is not valid; (3) individual response to a standard dose of heparin is unpredictable, both in duration and maximum effect; and (4) intraoperative monitoring of the heparin effect is practical and is the only way that any consistent, specific and point of heparin can be achieved.