The effect of nitrous oxide on the median lethal dose (LD50) of intravenously injected air was studied in rabbits. Determinations were performed in similar animal groups anesthetized with 1.0 per cent halothane and with 0.5 per cent halothane combined with 72-76 per cent nitrous oxide. In the halothane group, the LD50 was 0.55 ml./kg. In the nitrous oxide group, the LD50 was 0.16 ml./kg. Difference in values is explained on the basis of the differential solubility of nitrous oxide and nitrogen in blood. The finding of a reduction in LD50 value by a factor of 3.4 shows good agreement with theoretical calculations. We suggest that it may be hazardous to administer high concentrations of nitrous oxide to patients in whom the possibility of air embolism exists.
(C) 1966 American Society of Anesthesiologists, Inc.