[Plasma level of the thiocyanate ion in sodium nitroprusside perfusion]

24 subjects were selected at random out of a group of 80 patients undergoing surgery under a hypotensive anaesthetic technique by means of nitroprusside perfusion; the variation of one of the metabolites, the thiocyanide ion, were assayed. Hypotension was of 30 to 380 minutes duration and mean dosage of 12,44 mg (1,99 mug/kg/min). SCN- assays were performed by means of an original technique, which is described in this publication, before any perfusion of nitroprusside, every 30 minutes during perfusion and 30 and 60 minutes after ending the perfusion. Results show that SCN- concentration is increasing during perfusion but not as much as compared with the toxic concentration. Major increase takes place 30 minutes after starting the perfusion (1,27 10(-4) M/l). Increase slows down then and remains on a plateau level until the end of the perfusion where it decreases. Those results allow to reject a toxicity risk related to an increase of SCN- during nitroprusside perfusion. However, the accidents reported after high dosage of NPS and probably related to cyanogenic ion accumulation combined with lactic acidosis as shown in this publication, led the authors to advise a dosage not over 10 mug/kg/min in a maximum of 2 hours time.