What are the effects of CPB on hemostasis?
Patients undergoing CPB have a variety of hemostatic defects that lead to bleeding and the frequent need for transfusions. Dilution of the patient’s blood volume by the extracorporeal circuit priming solution causes depletion of platelets and a lowering of coagulation factor levels. Contact of blood with the extracorporeal circuit causes acti-vation of many systems. Contact activation causes intrinsic coagulation to begin, subsequently leading to the forma-tion of thrombin and fibrin. Then fibrinolysis ensues creating a subclinical disseminated intravascular coagula-tion (DIC) to occur. Sometimes this DIC is clinically evident and hemorrhage and thrombosis occurs. The formation of kallikrein, bradykinin, and complement leads to a “whole-body inflammatory reaction.” Platelet dysfunc-tion also occurs and is due to the effects of the extracorpo-real circuit on platelet membrane integrity and the effects of circulating platelet inhibitors. Heparin causes platelet activation and dysfunction. Protamine, given to reverse heparin’s effects, has antiplatelet properties and anticoagu-lant effects when given in excess.