Leucopenic effects of prolonged nitrous oxide treatment.

Studies of the leucopenic effects of nitrous oxide were made in rodents, with and without surgical wounds. The animals were exposed to one of the following atmospheres: (1) air; (2) 25 per cent nitrous oxide; (3) 60 per cent (rats) or 40 per cent (mice) nitrous oxide; the oxygen percentage was maintained at 21 per cent in each case. A leucopenic effect and suppression of the normal leucocytosis to trauma was seen with all concentrations of nitrous oxide after 2 days' treatment The effect of 60 per cent nitrous oxide was greater than 25 per cent nitrous oxide after 7 days but the difference was less pronounced in the first 4 days. The leucopenic effect was greater in animals with surgical wounds. Granulopenia was present after 3 days, but not after 1 day of nitrous oxide, and persisted for at least 3 days after completion of treatment. The safety of nitrous oxide therapy and its possible mechanisms of toxicity are discussed.