Nitrous oxide reduces thiopental-induced prolongation of survival in hypoxic and anoxic mice.

Arnfred's mouse model was used to test the effect of thiopental during hypoxia (5% O2) and anoxia, with and without simultaneous administration of nitrous oxide. As found by Arnfred and others, thiopental without N2O more than doubled survival time during hypoxia (from 5.2 +/- 0.6 to 13.9 +/- 2.6 min). This effect was completely offset by simultaneous use of N2O (from 13.9 +/- 2.6 to 4.8 +/- 0.7 min). Thiopental without N2O also increased survival time during complete anoxia (from 26 +/- 1 to 59 +/- 1 sec). This effect was diminished by 58% when N2O was added (from 59 +/- 1 to 40 +/- 1 sec). We conclude that nitrous oxide diminishes the effect of barbiturates upon survival time in hypoxic and anoxic mice.