The anesthetic effect of oxygen.

Low pressures of O2 (3 to 5 atm) cause convulsions in mice but higher pressures produce a state very similar to anesthesia. The authors estimated the anesthetic potency of O2 in mice which were exposed to either N2O alone, N2O + NaBr, or O2 + NaBr. From the dose-response curves, ED50S were derived for the gases. The ED50 for N5O alone was 1.50 +/- 0.036 atm (n = 12) and 1.11 +/- 0.041 atm (n = 12) in the presence of NaBr, a reduction of 25 percent. The O2 ED50 with NaBr was 3.91 +/- 0.077 atm (n = 12). After correction for the NaBr, the ED50 of O2 is estimated at 5.3 atm. This is lower than predicted from the lipid solubility of O2.