Nitroprusside-Induced Formation of Cyanide and Its Detoxication with Thiosulfate During Deliberate Hypotension

Publisher Website
Google Scholar
Abstract
Infusion of sodium nitroprusside (SNP) leads to the formation of cyanide, which is potentially toxic for the patient. The extent of cyanide formation as a function of the SNP dose, and the protective effect of simultaneously administered thiosulfate were investigated in 55 patients in whom controlled hypotension was induced during surgery. 17 patients (group I) received less than 2 μg/kg/min of SNP, 14 patients (group II) 2–4 μg/kg/min, and 8 patients (group III) more than 4 μg/kg/min. In 8 cases (group IV), bolus injections of thiosulfate were given intermittently at hourly intervals. Eight patients (group V) were given an infusion of a mixture of SNP and thiosulfate (ratio by weight 1:8.3), which was administered with the aid of light-protected perfusing sets. The mean maximum cyanide concentrations in the red blood cells were 4.5 ± 1.1 nmol/ml for group I, 14.4 ± 2.9 nmol/ml for group II, and 48.2 ± 11.0 nmol/ml (mean ± SEM) for group III. In group I almost all the individual figures were less than 10 nmol/ml, in groups II and III the cyanide level increased with the rate of infusion and with the total dose (mg/kg). In group IV, the maximal cyanide levels were 13.0 ± 5.0 nmol/ml at a mean infusion rate of 4.79 ± 1.10 μg/kg/min. In group V, despite higher rates of infusion (5.56 ± 0.77 μg/kg/min), no cyanide levels in excess of 10 nmol/ml were found; the mean value was 5.7 ± 0.8 nmol/ml. These findings show that even with moderately long durations of administration (2–3 h), markedly elevated cyanide levels can result from SNP infusion rates in excess of 4–5 μg/kg/min. An infusion of a mixture of SNP and thiosulfate reliably prevents such SNP-induced increases in cyanide levels. If opaque perfusing sets are employed, such infusions can be carried out without any problems arising.