The Value of Activated Coagulation Time in Monitoring Heparin Therapy During Extracorporeal Circulation

The anticoagulant effect of heparin was studied in 20 patients undergoing aortocoronary bypass surgery. The protamine dose necessary to reverse heparin after extracorporeal circulation (ECC) was assessed in ten patients from individual heparin dose-response curves (HDR group). The other ten patients received protamine according to a routine protocol (control group). The protamine administration was followed in both groups by injection of 3-5 g tranexamic acid (Cyklokapron). A wide range of sensitivity to heparin was shown by the patients. Although almost twice as much protamine was given to the control group as to the HDR group, the effect on heparin reversal was similar. The variability of protamine dose did not influence the post-bypass levels of fibrinogen, AT-III, activated coagulation time (ACT) or Cephotest, and fibrinolysis was not observed in either of the groups. During ECC there was poor correlation between ACT and plasma heparin levels, and the use of heparin dose-response curves was grossly misleading in regard to true heparin concentration. The postoperative bleeding was not related to the levels of heparin or coagulation parameters after heparin reversal. The concentrations of fibrinogen and AT-III showed variations dependent on the changes in haematocrit. A number of factors other than heparin that influence ACT are discussed.