Platelet preservation during cardiopulmonary bypass with aprotinin

A remarkable reduction of postoperative blood loss after cardiopulmonary bypass (CPB) has been achieved by prophylactic treatment with the proteinase inhibitor aprotinin. To reveal the mode of action of aprotinin, 23 CPB patients were randomised for aprotinin (2 x 10(6) KIU in the pump prime) or placebo treatment during CPB. Blood samples were collected before and during operation. Blood loss and blood requirements were 50% lower in the aprotinin treated patients than in the untreated patients. The adhesive capacity of platelets assessed by the amount of platelet membrane glycoprotein Ib (GP Ib) decreased by 50% in the untreated patients within 5 min of CPB and remained low during CPB, whereas GP Ib did not decrease in the aprotinin treated patients. Fibrinogen degradation products indicating plasmin activity could only be measured after 30 min of CPB in the untreated, but not in the aprotinin treated patients. The kallikrein inhibiting capacity was 34% decreased in the untreated patients within 5 min of CPB, while it increased by 84% and remained high during CPB in the aprotinin treated patients. Our results demonstrate that the improved haemostasis during and after CPB in patients treated with aprotinin can be attributed to the preserved adhesive capacity of platelets. It remains to be found whether aprotinin has a primary effect on platelets or a secondary effect by plasmin or kallikrein inhibition.