Effect of nitrous oxide on serum vitamin-B12 levels under surgical anesthesia

To evaluate the effect of nitrous oxide (66%) as used in surgical anesthesia on serum vitamin-B12 levels, 27 patients were studied undergoing operations longer than 2 hours. In addition a group of 10 patients was given oxygen/halothane for comparison. In patients receiving nitrous oxide, serum-B12 concentrations showed significant reductions during anesthesia, but increased at the 24th hour and recovered completely at the 72nd hour postoperatively. No significant changes were seen in vitamin levels during and after anesthesia in patients not receiving nitrous oxide. There was also no macrocytosis or hypersegmentation of neutrophils on blood slides taken concomitantly with blood samples in both groups. In view of the rapid recovery of vitamin levels and the fact that, in spite of the significant reductions caused by nitrous oxide none of the individual values decreased below normal, it is suggested that the effect of nitrous oxide as used in surgical anesthesia may be considered insignificant in patients with normal vitamin-B12 values.