POTENCY OF MIXTURES OF GENERAL ANAESTHETIC AGENTS

The anaesthetic potencies of binary mixtures of the gases argon (Ar), nitrous oxide (N 2 O) and sulphur hexafluoride (SF 6 ) have been measured using mice. The mixtures SF 6 -N 2 O and N 2 O-Ar showed additive behaviour, whereas the constituents of the mixture SF 6 -Ar were non-additive, having a smaller total potency than expected. Further experiments on this mixture with Italian Great Newts and on the carbon tetrafluoride mixtures CF 4 -Ar and CF 4 -SF 6 with mice suggested that the anomalous potencies may arise from specific pulmonary effects associated with the breathing of SF 6 accompanied by a high pressure of some other gas.