Transient adhesion of platelets in pump-oxygenator systems: influence of SMA and nitric oxide treatments

We employed gamma scintigraphy to quantify the transient accumulations of p latelets in pump-oxygenator systems employed in cardiopulmonary bypass (CPB ). A flat sheet microporous polypropylene membrane oxygenator (Cobe Due) wa s employed, with and without siloxane/caprolactone oligomer coating (SMA) ( n = 8 each). The effect of nitric oxide gas infusion on platelet deposition was also evaluated for the uncoated Cobe Duo system (n = 10 each). Scintig raphic images of radiolabelled cells were obtained and converted to numbers of all platelets, labeled and unlabeled. adhering to the pump and oxygenat or surfaces. These numbers were compared, by study group, for a 90-min peri od of normothermic CPB in the adult pig, employing standard prime and antic oagulation regimens. Platelets adhered in large numbers to control oxygenat ors, reaching maxima (>20% of the circulating platelet mass) 30 min followi ng institution of CPB, and decreasing for the duration of CPB. SMA treatmen t significantly decreased platelet adhesion following a 5-10-min transient accumulation period. Nitric oxide infusion significantly reduced platelet a dhesion throughout the CPB period. Platelet accumulations on the high fluid shear centrifugal pump surfaces increased monotonically to maxima at about the same time as for the oxygenators, but did not decrease thereafter. Hig her platelet surface densities were observed on the centrifugal pump surfac es than on the oxygenator surfaces. CPB with the untreated circuit tended t o reduce circulating platelet counts vs theoretical values based on hemodil ution alone. In contrast, SMA significantly increased the circulating plate let count versus the untreated control group. These results indicate that p latelet adherence to the foreign surfaces of CPB equipment are influenced i n characteristic ways by time and fluid shear. SMA treatment and nitric oxi de infusion both reduce platelet adhesion to oxygenator surfaces. SMA treat ment spares these cells for the circulation.