Activated clotting time for control of anticoagulation during surgery.

Two groups of patients undergoing extracorporeal bypass were compared for heparin activity and for heparin and protamine dosage. In group I (18 patients), a uniform dosage pattern was neutralized at the end to a normal clotting time. In group II (43 patients), heparin and terminal protamine doses were regulated by activated clotting times (ACT) using a Hemochron (International Technidyne Corp., Metuchen, NJ). In group II there was a 39 per cent reduction of total heparin dose per case, protamine was reduced 76 per cent, and if the initial heparin doses were excluded, maintenance heparin was reduced 73 per cent. No pattern of heparin administration could be applied to all patients. Heparin half-life varied from 43 to 220 minutes. Other factors that alter heparin activity during bypass revealed no statistical differences. Plasma Hgb was significantly higher in group I, and platelet counts the day following operation were higher in group II. ACT allows tailoring heparin and protamine without the unnecessary dangers of variations in patient response and drug potency.