Relationship of platelet aggregation to bleeding after cardiopulmonary bypass

Excessive bleeding after cardiopulmonary bypass operations is a persistent problem. This study assessed the influence of platelet function on blood loss for 134 patients undergoing cardiopulmonary bypass. Platelet function was measured by platelet aggregation in platelet-rich plasma and whole blood using collagen as the agonist. Adenosine triphosphate release was assessed concurrently. Measurements were made 1 day before operation and 1 hour after the cessation of cardiopulmonary bypass. Three important findings were made. First, statistically significant correlations were shown between preoperative and postoperative platelet aggregation and blood drainage for the first 3 hours postoperatively. Second, correlations were greatest when preoperative measurement was performed on whole blood and postoperative measurement was performed on platelet-rich plasma. Third, patients with reduced postoperative platelet aggregation in platelet-rich plasma had significantly greater transfusion requirements in the first 24 hours postoperatively. In defining the 16 patients who bled excessively among the 134 patients studied, the preoperative aggregation in whole blood had a sensitivity of 62%, specificity of 75%, positive predictive value of 26%, and negative predictive value of 94%. The postoperative aggregation in platelet-rich plasma had a sensitivity of 86%, specificity of 69%, positive predictive value of 28%, and negative predictive value of 97%. These results indicate that preoperative and postoperative measurement of platelet aggregation may provide a rationale for the prophylaxis or treatment of patients to reduce blood loss after cardiopulmonary bypass.