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

Abstract Background . The protein C system is important in the regulation of hemostasis. We studied its behavior during coronary artery bypass grafting procedures with and without aprotinin treatment using assays sensitive for activation 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 complexes between activated protein C with its two major plasma inhibitors, protein C inhibitor and α 1 -antitrypsin in patients treated with placebo (n = 17), low-dose (n = 15), and high-dose (n = 16) aprotinin during elective coronary artery bypass grafting. Results . The levels of proteins C and S showed a rapid decrease after heparinization, decreased greatly after start of cardiopulmonary bypass, and remained stable during cardiopulmonary bypass. Activated protein C inhibitor complexes were markedly elevated at the start of the procedure. Activated protein C–α 1 -antitrypsin decreased greatly after the start of cardiopulmonary bypass and remained stable during cardiopulmonary bypass. A significant peak was observed at the intensive care unit. Activated protein C–protein 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 measured patterns. Conclusions . In this study no evidence was found for increased activation of the protein C system during coronary artery bypass grafting. Administration of aprotinin did not result in different patterns of activation of the protein C system.