The influence of the duration of cardiopulmonary bypass on coagulation, fibrinolysis and platelet function.

BACKGROUND: The duration of cardiopulmonary bypass (CPB) might influence blood coagulation. This appears particularly relevant in the light of new, less invasive techniques that propose smaller incisions at the expense of a possible prolongation of time on CPB. METHODS: The time-dependent effects on coagulation, fibrinolysis and platelet function were investigated in 94 patients scheduled for elective coronary artery bypass grafting. Tests on coagulation, fibrinolysis, and platelet function (flow cytometric assay of expression densities of glycoprotein IIb/IIIa and P-selection were performed the day before surgery and after completion of surgery. RESULTS: A significant correlation was found between the duration of CPB and parameters of increased coagulation, decrease of platelet counts during CPB and platelet function. Longer duration of CPB led to an increased need for transfusion of red blood cells. CONCLUSIONS: The duration of CPB affects thrombin formation as well as platelet count and function, but not the fibrinolytic system. This may prove to be a disadvantage when employing minimally invasive techniques that prolong the duration of CPB.

Effects of extracorporeal circulation and heparin on the phenotype of platelet surface antigens following heart surgery.

In this prospective study, the time-dependent effects of extracorporeal circulation and heparin-mediated effects on platelet surface antigens in vitro were investigated using whole blood flow cytometry. Blood samples were drawn prior to and following extracorporeal circulation in 89 patients. The response of surface antigen expression (glycoprotein IIb/IIIa, P-selectin, and glycoprotein Ib) with and without in vitro stimulation was measured. A significant correlation of the duration of extracorporeal circulation with the postoperative response of glycoprotein IIb/IIIa, glycoprotein Ib, and P-selectin to in vitro activation was found. Postoperative P-selectin and glycoprotein Ib expression stimulated with ADP correlated to blood loss. Heparin in vitro significantly reduced glycoprotein Ib expression. Heparin, as well as the duration of extracorporeal circulation, independently correlated to phenotypic changes of platelets following extracorporeal circulation. The significant correlation of these variables to postoperative blood loss demonstrates their relevance to platelet function in vivo.

Predictors of blood loss after coronary artery bypass grafting.

OBJECTIVE: To assess the predictive value of variables possibly associated with blood loss after coronary artery bypass grafting (CABG). DESIGN: A prospective study. SETTING: A university hospital. PARTICIPANTS: Eighty-nine patients scheduled for elective CABG. INTERVENTIONS: Blood samples were drawn before and after surgery. Chest tube drainage was measured hourly until removal of drains. MEASUREMENTS AND MAIN RESULTS: Activation of coagulation and fibrinolysis, routine clotting tests, and expression of platelet surface antigens were analyzed using flow cytometry. A significant correlation was found among blood loss and activated partial thromboplastin time, fibrinogen, prothrombin fragment 1 + 2, D-dimers, platelet count, GPIb and P-selectin expression on platelets, use of internal thoracic artery, cross-clamp time, and thrombin-antithrombin III complex. In a multiple regression model, glycoprotein (GP) Ib expression on platelets, platelet count, use of internal thoracic artery, and D-dimers were significantly associated with blood loss. Logistic regression analysis showed that GPIb and D-dimers predicted an increased blood loss with a positive predictive value of 73% and a negative predictive value of 91%. CONCLUSIONS: Postoperative D-dimers and GPIb expression may be useful to exclude nonsurgical causes in bleeding patients after CABG.