Canadian Journal of Anesthesia, Vol 24, 651-660, Copyright © 1977 by Canadian Anesthesiologists' Society

Cyanide Toxicity Following Nitroprusside Induced Hypotension

¹ Department of Anaesthesia and the Divisions of Biochemistry and Neurosurgery, Ottawa Civic, Hospital, Ottawa, Ontario, Canada

Address reprint request to Dr. Frances Smith, Division of Biochemistry, Ottawa Civic, Hospital, Ottawa, Ontario, Canada. K1Y 4E9

Several recently reported deaths following the use of sodium nitroprusside have been attributed to the accumulation of the nitroprusside metabolite, cyanide. In this study, brief nitroprusside infusions (mean = 36 minutes) were administered in currently recommended doses during intracranial surgery. The peak blood cyanide following the infusions was 65.2 ± 17.5 µ per cent (mean ± SE) (n = 13). It occurred within 45 minutes after infusion. The highest cyanide level detected was 205 µ per cent, which is within the range of reported lethal blood cyanide levels. Metabolic acidosis developed in the four patients with the highest blood cyanide levels (range 90-205 µ per cent). This occurred between 45 and 180 minutes following the cyanide peak. Blood ATP levels were depressed in the same patients. These findings are indicative of disturbed aerobic metabolism. We conclude that there is evidence of cyanide toxicity when nitroprusside is infused into patients using currently recommended doses. We recommend that for short infusions the dose of sodium nitroprusside should not exceed 0.5 mg/kg.