Effect of nitric oxide gas on platelets during open heart operations

The increased bleeding tendency observed after cardiopulmonary bypass is caused in part by thrombocytopenia and impaired platelet function induced by the procedure. Previous in vitro studies have shown that nitric oxide (NO) added to the oxygenator sweep gas reduces platelet activation during experimental perfusion. We evaluated the effect of 40 ppm of NO, added to the oxygenator sweep gas, on platelet consumption and activation in patients undergoing cardiopulmonary bypass.

Twenty patients scheduled to undergo cardiopulmonary bypass were randomized to either the control or the NO arm of the study. Their platelet count, plasma beta-thromboglobulin level, platelet membrane glycoprotein Ib and IIb/IIIa levels, adenosine diphosphate-induced platelet aggregation, plasma nitrate level, and plasma hemoglobin were assayed before, during, and after cardiopulmonary bypass.

After operation, slightly higher platelet counts were observed in the NO-treated patients than in the control patients, which might indicate a lower degree of platelet adhesion to the artificial surfaces of the extracorporeal circuit. However, this difference did not reach statistical significance. In addition, a difference in platelet membrane expression of glycoprotein Ib was seen between the NO and control groups after operation; the platelets of the control patients had significantly higher glycoprotein Ib expression than those of the NO-treated patients. The results of platelet aggregometry indicated preserved platelet function in both the NO-treated and control patients. The blood methemoglobin levels also were low in both groups.

Nitric oxide might reduce the platelet consumption encountered during cardiopulmonary bypass without having any adverse effect on platelet function, as reflected by the preserved aggregation response seen in our patients. However, the best route of NO administration and the optimum dose remain to be established.