Platelet mapping as part of modified thromboelastography (TEG®) in patients undergoing cardiac surgery and cardiopulmonary bypass.

The platelet-mapping assay of the thromboelastograph was used to measure platelet aggregation and to examine the effect of cardiopulmonary bypass on multiple platelet receptors and the role of altered receptor activity in postoperative bleeding. The percentage platelet aggregation for collagen, adenosine diphosphate and arachidonic acid was measured in 40 patients divided post-hoc into high- or low-bleeding groups depending on postoperative 24-h chest tube output. Platelet aggregation was lower after cardiopulmonary bypass compared to before it using collagen (mean (SD) 45 (25) vs 19 (12)%, p<0.001), adenosine diphosphate (76 (23) vs 35 (24)%, p<0.001), and arachidonic acid (61 (33) vs 31 (35)%, p<0.001). Only platelet aggregation as measured using collagen pre- and post-cardiopulmonary bypass was significantly less in the high- compared to the low-bleeding group. This finding was significantly correlated with the 24-h chest tube drainage, and it predicted postoperative bleeding with a sensitivity of 83% and a specificity of 68%. Therefore, platelet aggregation is reduced following cardiopulmonary bypass, and this may play a role in predicting postoperative blood loss.