Metabolism of sodium nitroprusside in dogs awake and anesthetized with halothane

[Blood and urinary cyanide concentrations during long-term sodium nitroprusside perfusion]

Five deeply comatose neurological patients were administered a continuous perfusion of sodium nitroprusside (SNP) at the rate of 3 microgram.kg-1.min-1. The levels of blood cyanide (CN-) were measured two hours after the start, then every 12 hours during, and 12 and 24 hours after the end of perfusion. The urinary output of CN- was also studied. The results show that total blood CN- stabilized after 36 hours to a mean value of 0.11 mg/l. When perfusion was stopped, CN- blood levels dropped but did not reach pre-perfusion values at the 24th hour. Urinary excretion of CN- which reached a maximum value of 0.050 mg/24 h represents a negligible amount and does not explain the fall of blood CN- and the occurrence of a concentration plateau. The results showing lower values obtained on non-anesthetized patients during the first hours of perfusion compared to those of a previous study done under neuroleptanaesthesia are discussed. These results suggest that prolonged perfusions at SNP at the rate of 0.177 mg.kg-1.h-1 do not produce toxic blood level of CN-.