Metabolism of sodium nitroprusside in dogs awake and anesthetized with halothane

Sodium nitroprusside (SNP) is rapidly metabolized to cyanide (CN) and thiocyanate (SCN). The authors determined the rates of CN and SCN production during SNP infusion sufficient to maintain blood pressure at 80 per cent of baseline in the dog awake and during halothane anesthesia. Each dog served as its own control. The endogenous whole-blood CN concentration was significantly lower in anesthetized dogs (0.6 nmol/ml) than awake dogs (1.8 nmol/ml). CN concentration increased similarly during SNP infusion in awake (4.5 nmol/ml) and anesthetized dogs (2.3 nmol/ml). In another group of dogs, whole-blood CN concentration decreased significantly due to halothane anesthesia. The regression coefficient was -0.21 nmol CN/ml/hr. There was no significant difference in plasma SCN concentration following infusion of SNP in both awake (33 nmol/ml) and anesthetized dogs (26 nmol/ml). The cause of this decreased blood CN concentration with or without SNP infusion during halothane anesthesia is not known.