Infusion of sodium nitroprusside induces platelet dysfunction in vitro

The effect of sodium nitroprusside (SNP) infusion on platelet function was prospectively evaluated in 29 patients undergoing cardiac surgical procedures requiring cardiopulmonary bypass. Any patient receiving preoperative medication known to interfere with platelet function was excluded from this study. Platelet function was evaluated by measurement of platelet aggregation with both adenosine diphosphate (ADP) and epinephrine-induced aggregation tests. Ten patients served as a control population receiving fentanyl anesthesia and no SNP. Nineteen patients received SNP, as clinically indicated, following the induction of anesthesia (and prior to cardiopulmonary bypass) to maintain a mean blood pressure of 80 mmHg. The infusion rate and total dose of SNP delivered was recorded for each patient. Infusion rates of SNP greater than or equal to 3 micrograms.kg.-1 min-1 resulted in a dose-related decrease in platelet aggregation (P less than 0.05). This reduction in platelet function was accompanied by a concomitant increase in bleeding time from 5.8 +/- 0.6 to 9.3 +/- 0.4 min in the patients receiving SNP (P less than 0.05). In addition, with the administration of a total dose of SNP greater than or equal to 16 mg, a significant reduction in platelet aggregation (P less than 0.05) was observed. Platelet aggregation studies and bleeding time performed in the control group (following the administration of fentanyl (30 micrograms/kg) did not reveal any deviation from baseline values. The results from this in vivo study support previous in vitro data demonstrating a detrimental effect upon platelet function following SNP infusion.