Invited commentary

Abstract

Tranexamic acid and aprotinin are routinely used to reduce bleeding in cardiac surgery. Aprotinin is a serine protease inhibitor of low molecular weight, isolated from bovine lung. In a high dose formulation, the Hammersmith group showed that it was effective in reducing the need for blood transfusion in adults undergoing redo surgery or surgery for infective endocarditis and in primary coronary surgery. But it was not long before surgeons ran into problems with control of the clotting time in some patients receiving aprotonin. There are two methods commonly used for automatic clotting times. They use different systems for activation of coagulation and monitoring of the time to clot formation. Hemochron (International Techdyne Corporation, Edison, NJ) uses celite as the activator. The Hemo-Tec system (Hemo-Tec Inc, Englewood, CO.) uses kaolin as the activator. There are significant differences between results when these instruments are used on the same blood sample drawn during open heart surgery and when aprotinin is administered to the heparinised patient on cardiopulmonary bypass. This is due to the effect of the activator. Kaolin is a very powerful activator of the intrinsic coagulation system and therefore aprotinin has little effect on activation in its presence whereas clotting induced by contact with other surfaces is inhibited by aprotinin.