Blood cyanide and thiocyanate concentrations after administration of sodium nitroprusside as hypotensive agent in neurosurgery.

In a group of 50 neurosurgical patients receiving sodium nitroprusside as a hypotensive agent, in doses of 50--2131 microgram/kg body weight, whole blood cyanide was estimated before infusion of drug, during infusion, immediately after infusion, and 1 and 3 h later. Cyanide values increased significantly, reaching the maximum in a sample taken immediately after infusion (mean value, 333; highest value, 1800 microgram/liter). Values correlated closely with both dose and rate of infusion. Blood thiocyanate, estimated before, immediately after, and 3 h after the infusion, showed no significant changes in thiocyanate concentration. In any case, no signs or symptoms of cyanide or thiocyanate poisoning were observed. We conclude that sodium nitroprusside, in the proper dose and given at the proper rate, does not precipitate cyanide poisoning.