ANTICOAGULATION IN CARDIOPULMONARY BYPASS

Abstract

Prolonging the whole blood clotting time (WBCT) 2 to 3 times normal is said to provide a “safe” level of anticoagulation during cardiopulmonary bypass. To test this level of anticoagulation 9 monkeys were anticoagulated with heparin at the start of cardiopulmonary bypass so that WBCT's ranged from 201 sec to > 1000 sec (normal 91 sec). WBCT, platelet count (P), fibrinogen concentrations (F), and fibrin monomer concentrations (FM) were measured at 10, 30, 60, 90, and 120 minutes during bypass. Antithrombin III levels (AT3) were measured before and after bypass. Six monkeys developed increased FM indicating active coagulation beginning from 10 to 60 minutes on bypass. WBCT's were > 200 sec in all animals at the time of FM detection. P fell below 100,000/mm3 in the 6 animals with elevated FM, but remained above 100,000/mm3 in the other 3 animals. The mean value of AT3 decreased from 69% before, to 24.4% after bypass in the 6 animals with elevated FM, but was 61% after bypass in the others. F decreased from 167 mgm% to 80.5 mgm% in monkeys with elevated FM and to 117 mgm% in those with normal FM concentrations. Excessive bleeding did not occur in the animals without increased FM though WBCT's were in excess of 1000 sec. The results suggest that prolonging the WBCT 2 to 3 times normal is not sufficient anticoagulation to prevent activation of clotting during cardiopulmonary bypass.