Sodium nitroprusside metabolism in children during hypothermic cardiopulmonary bypass

Ten children, aged 1-7 yr, presenting for repair of complex congenital heart lesions, were prospectively studied. A ketamine, halothane/isoflurane, and fentanyl anesthetic was used. After initiation of hypothermic cardiopulmonary bypass, sodium nitroprusside (SNP) was titrated as necessary to maintain a target mean arterial blood pressure of 35-60 mm Hg. Blood samples drawn immediately prior to starting SNP infusion, every 15 min during infusion, and at 1, 4, and 24 h postinfusion were analyzed for whole blood cyanide (CN) and serum thiocyanate (SCN). Blood gas analysis was performed every 30 min during SNP infusion. A maximum CN level ≥1.0 μg/mL was observed in two children; four others had maximum CN levels between 0.5 μg/mL and 1.0 μg/mL (normal, <0.2 μg/mL). No child had a clinically important increase of SCN subsequent to SNP in fusion. There was substantial variability in observed CN accumulation during SNP infusion. CN levels during the first 60 min correlated with the average SNP rate of administration (P = 0.02). Cyanide levels rapidly decreased after termination of SNP infusion and were undetectable 4 h postinfusion. Despite the short-term increase of CN level, no child showed biochemical signs of toxicity (acidosis or increased mixed venous oxygen tension).