Activation of the protein C system during cardiopulmonary bypass with and without aprotinin

Background. The protein C system is important in the regulation of hemostas is. We studied its behavior during coronary artery bypass grafting procedur es with and without aprotinin treatment using assays sensitive for activati on of the protein C system. Methods. In a prospective, double-blind, randomized study of 48 patients we investigated the levels of antigen to proteins C and S and of the complexe s between activated protein C with its two major plasma inhibitors, protein C inhibitor and alpha(1)-antitrypsin in patients treated with placebo (n = 17), low-dose (n = 15), and high-dose (n = 16) aprotinin during elective c oronary artery bypass grafting. Results. The levels of proteins C and S showed a rapid decrease after hepar inization, decreased greatly after start of cardiopulmonary bypass, and rem ained stable during cardiopulmonary bypass. Activated protein C inhibitor c omplexes were markedly elevated at the start of the procedure. Activated pr otein C-alpha(1)-antitrypsin decreased greatly after the start of cardiopul monary bypass and remained stable during cardiopulmonary bypass. A signific ant peak was observed at the intensive care unit. Activated protein C-prote in C inhibitor levels showed a peak after heparinization in accordance with the accelerating effect of heparin on the complex formation but decreased thereafter. Treatment with aprotinin did not notably alter any of the measu red patterns. Conclusions. In this study no evidence was found for increased activation o f the protein C system during coronary artery bypass grafting. Administrati on of aprotinin did not result in different patterns of activation of the p rotein C system. (C) 1998 by The Society of Thoracic Surgeons.