Hemostatic-endothelial interactions: a potential anticoagulant role of the endothelium in the pulmonary circulation during cardiac surgery.
The use of extracorporeal circulation during cardiopulmonary bypass (CPB) procedures is associated with significant morbidity and mortality. Exposure of blood to the foreign surface of the extracorporeal circuit results in activation of complement, kinin, fibrinolytic and coagulation systems as well as cellular mediators of inflammation. Without the use of anticoagulants, the extracorporeal circuit would clot; high-dose heparin prevents coagulation, but activation of the coagulation system and consequent thrombin generation still occur. During CPB, the lungs are effectively removed from the circulation, and, hence, heparinized blood remains static within the pulmonary vasculature for this period. It was postulated that under these conditions, the hemostatic system may become activated and could contribute to pulmonary dysfunction in some patients after CPB. However, it appears that during CPB interactions among heparin, the hemostatic system, and the endothelium may exert a protective effect, at least against activation of the tissue factor coagulation pathway. In this article, the effect of CPB on the coagulation system, with particular reference to changes in coagulation proteins occurring in the pulmonary vasculature, are reviewed.