Estimation of Minimum Heparin Circulation Time for Activated Clotting Time Determination

Prior to commencing cardiopulmonary bypass (CPB) anticoagulation is generally monitored by the activated clotting time (ACT). Serial ACT estimations at one minute time intervals were performed on 50 CPB patients following heparinization to establish the time required for heparin circulation and for elevation of the ACT to a preset target value of 400 seconds. The results showed that adequate anticoagulation for cannulation to proceed was achieved in 86% of samples taken one minute following heparinization. Confirmation of adequate anticoagulation at one minute would allow earlier cannulation in an emergency situation and alert the cardiac team if the heparin failed to enter the systemic circulation. Patients in whom ACT values failed to reach the target value at one minute subsequently required additional heparin, immediately, or at a later stage.