Platelet membrane receptors during short cardiopulmonary bypass--a flow cytometric study

To elucidate a mechanism of platelet dysfunction during extracorporeal circulation, we performed a study on the surface expression of platelet adhesive receptors (GPIb, GPIIb-IIIa) and activation markers (GMP140, GP53) during short cardiopulmonary bypass (CPB). Ten paediatric patients, age 6-13 years, with atrial or atrioventricular septal defects were studied. The mean CPB time was 52 min (21-110 min). During CPB, a significant drop in platelet count was observed, but not below 130 x 10(3)/microliter. The expression of platelet GPIb decreased slightly during CPB and the decrease was not significant. The decrease of GPIIb-IIIa was significant, but only in samples collected either at the end of CPB (89 +/- 13%, p < 0.05) or before leaving the operating room (74 +/- 14%, p < 0.05). The value of surface expression of platelet activation markers (GMP140, GP53) during CPB was in the range of values for resting platelets. Our results suggest that generalized CPB-induced defects of primary haemostasis are not directly connected to circulation of activated degranulated platelets or to loss of platelet adhesive receptors GPIb-IX and GPIIb-IIIa.