Platelet Reactivity During Carciopulmonary Bypass : Marked Reduction Followed by Early Restitution

• INTRODUCTION. Cardiopulmonary bypass (CPB) affects platelets, and platelet dysfunction is considered to be an important risk factor for post-operative bleeding after coronary artery bypass graft (CABG) surgery. Monitoring platelet function in the peri-operative period therefore is of importance to reduce morbidity due to both bleeding and post-operative graft occlusion. Our aim was to study platelet reactivity in CABG patients in the peri-operative period.METHODS. Platelet function in 30 patients undergoing CABG was analyzed using an impedance aggregometry point-of-care (POC) instrument (Multiplate). Platelet reactivity was measured preoperatively at induction of anaesthesia, preoperatively immediately before CPB, after 30 minutes of CPB, after end of CPB, postoperatively at arrival to the ICU and finally at 3 and 18 h after surgery. Whole blood platelet aggregation was measured after activation with ADP (adenosin diphosphate), TRAP (thrombin receptor activating peptide), AA (arachidonic acid) and collagen. Platelet count was measured, and circulating platelet pool was assessed by correcting for hemodilution by indexing to hemoglobin. Non-parametric statistics were used, results are presented as median and 25–75%-percentiles.RESULTS. Reactivity to ADP, TRAP and AA agonists was significantly reduced at 30 min of CPB and at the end of CPB, followed by a rapid increase after CPB to preoperative values. Collagen showed a similar, but not significant, decrease during CPB followed by a post-CPB increase to values above baseline (p\0.001). Platelet count dropped after 30 min of CPB from 240 (204–301) preoperatively to 150 (132–189) after 30 min of CPB and further to 134 (120–151) 9 109/L at the end of CPB (p\0.001). Corrected for blood loss and hemodilution there was a reduced platelet pool at the end of CPB and at arrival at the ICU (p\0.001)CONCLUSION. There is an early decrease in platelet reactivity during CPB followed by a rapid post-CPB restitution of platelet function, despite low preoperative aggregometry values and lower post-CPB platelet count. The rapid preoperative changes in aggregometry points to a possible role for POC analysis of hemostatic function. The post-CPB increase in platelet reactivity simultaneously to the decrease in platelet count could imply increased aggregating tendency for remaining platelets, with possible implications for early graft failure and postoperative anti-platelet therapy.

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