Cardiopulmonary bypass and activation of antithrombotic plasma protein C

Objective: We hypothesized that antithrombotic plasma-activated protein G p lays a defensive antithrombotic role during coronary ischemia and postische mic reperfusion, Methods and results: We evaluated protein C activation dur ing cardiopulmonary bypass and coronary reperfusion in 20 patients undergoi ng coronary bypass surgery. During cardiopulmonary bypass and during the 10 minutes after aortic unclamping, the plasma levels of protein C (mean +/- standard error of the mean) decreased from 123% +/- 7% to 74% +/- 5% of nor mal mean. In contrast, the levels of activated protein C in plasma increase d from 122% +/- 8% to 159% +/- 21%, and the activated protein C/protein C r atio increased from 1.04 +/- 0.08 to 2.29 +/- 0.31 (P = .006, 2-tailed Wilc oxon signed rank test). patients were stratified on the basis of the increa se in activated. protein C in the coronary sinus plasma at 10 minutes after reperfusion by means of the arbitrary value of 1.5 for the activated prote in C/protein C ratio, Within 24 hours, the patients with low increases in a ctivated protein C (ratio < 1.5, n = 8) had a significantly (P < .05) lower cardiac output and mean pulmonary artery pressure, as well as a higher sys temic vascular resistance, than patients (n = 11) with high increases in ac tivated protein C (ratio > 1.5). The rapid increase in activated protein C during the first 10 minutes after aortic unclamping indicated protein C act ivation in the reperfused vascular beds. Conclusions: The antithrombotic pr otein C pathway was significantly activated during cardiopulmonary bypass m ainly during the minutes after aortic unclamping in the ischemic vascular b eds. Suboptimal protein C activation during ischemia may impair the postisc hemic recovery of human heart and circulation.