Heparin, Platelet Aggregation, Neutrophils, and Cardiopulmonary Bypass

Cardiopulmonary bypass (CPB) is associated with both neutrophil activation and failure of platelets to form large stable aggregates. We aimed to determine the effects of heparin and of neutrophil activation on platelet aggregation in whole blood. Fourteen patients undergoing routine aortocoronary bypass grafting and NSAID-free for over 7 days were studied before and after heparinisation, and at end-CPB. Whole blood, anticoagulated with rHirudin, was stirred for 3 minutes, and macroaggregation in response to collagen (0.6 μg.mL −1) or the neutrophil stimulant fMLP (10 −7M) was determined by whole blood impedance aggregometry. Microaggregation was measured by counting unaggregated single platelets (corrected for haemodilution). The blood of volunteers n=14 was studied in vitro. Patients: Before CPB, heparin effectively abolished platelet macroaggregation induced by collagen (20.5 to 1.4 Ω) or fMLP (3.9 to 0 Ω) ( p