Alterations in coagulation and fibrinolysis associated with cardiopulmonary bypass during open heart surgery

The effect of heparin as an anticoagulant was examined and the extent of fibrinolytic activity during cardiopulmonary bypass (CPB) was measured. Twenty patients undergoing valve replacement or aortocoronary bypass surgery were studied. Fibrinopeptide A (FPA) levels gradually became elevated as CPB proceeded, and antithrombin III (AT III) decreased during CPB. This indicates that despite the use of heparin, the coagulation system was activated, leading to fibrin formation in the microcirculation. On the other hand, fibrinopeptide B (FPB beta 15-42) also increased to four times the preoperative value at two hours on CPB. Intrinsic fibrinolytic activity, as determined by the activity of kaolin-activated euglobulin, was transiently increased only at the beginning of CPB. The C1 inactivator-resistant fibrinolytic activity and tissue plasminogen activator antigen (t-PA;Ag) increased sharply during CPB and reached maximum levels one hour after the start of CPB, indicating that enhanced fibrinolytic activity during CPB is predominantly of extrinsic origin as the result of t-PA release from the vascular walls. It is concluded from the above findings that thrombin activity continues during CPB. Enhanced fibrinolytic activity during CPB appears to be important because t-PA activates plasminogen predominantly where fibrin is formed, leading to dissolution of the microthrombi formed during CPB.