PREVENTION OF FETAL AND MATERNAL CYANIDE TOXICITY FROM NITROPRUSSIDE WITH COINFUSION OF SODIUM THIOSULFATE IN GRAVID EWES

Coadministration of sodium thiosulfate with sodium nitroprusside (SNP) to children and adults prevents increases in cyanide concentrations d uring anesthesia or long-term SNP infusions. We wondered whether mater nally administered sodium thiosulfate would prevent increases in fetal red cell cyanide concentrations in gravid ewes receiving SNP infusion s. Under anesthesia, the fetal head was delivered through a lateral hy sterotomy for catheterization of the jugular vein; the fetus was left in utero. Six control ewes near term received SNP at 25 mu g.kg(-1).mi n(-1) for 4 h. Norepinephrine was used to maintain maternal mean arter ial pressure at 80% baseline values. Six experimental ewes received th e same treatment except that sodium thiosulfate was infused with SNP ( 1 g sodium thiosulfate per 100 mg SNP). Serial red cell cyanide concen trations in ewes and fetuses were followed. One control fetal death re sulted from abruptio placenta, and this ewe and fetus were excluded fr om analysis. An additional control ewe and fetus died from apparent cy anide poisoning late during the course of the experiment. While contro l ewes and fetuses suffered progressive increases in red cell cyanide concentrations into the toxic range, experimental ewes and fetuses nev er developed toxic red cell cyanide levels (ewes P <.003, fetuses P <. 004). These data, if applicable to humans, suggest that coadministrati on of sodium thiosulfate with SNP to pregnant women at doses currently in use for nonpregnant patients will prevent fetal, as well as matern al, cyanide toxicity.