Teratogenicity of nitrous oxide

Nitrous oxide (N2O) is the only inhalation anaesthetic that has definitely been shown to be teratogenic in experimental animals. Studies to date indicate that there may be many mechanisms contributing to this effect. Two of the major contributing factors are N2O-induced methionine synthase inhibition and sympathomimetic effects. N2O-induced methionine synthase inhibition leads to reduced DNA synthesis and methylation reactions. The latter is a particularly important factor in teratogenic outcomes. N2O-induced sympathomimetic effects lead to decreased maternal uterine blood flow and the direct stimulation of α1 adrenoceptors in the embryo. The former partially contributes to resorption (embryonic/fetal death), and the latter to situs inversus (impairment of left–right body axis development). Contrary to the findings from animal studies, the teratogenic potential of N2O in humans has not been well established. Epidemiological studies suggest that N2O does not cause a teratogenic effect in clinical circumstances.