Pressure antagonism of anaesthetic-induced conduction failure in frog peripheral nerve

Experiments to investigate pressure-induced antagonism of the effects of general anaesthetics in isolated peripheral nerve from the frog are described. The doses of four gaseous general anaesthetic agents required to reduce electrically evoked action potentials by 50% (mean +/- SEM) were nitrous oxide 490 +/- 40.4 kPa, ethylene 665 +/- 212 kPa, dichlorodifluoromethane 108 +/- 17.2 kPa and cyclopropane 70 +/- 5 kPa. The combination of high pressure and the anaesthetic agent partially or completely restored the action potential amplitudes for the gaseous and some of the volatile agents (chloroform, diethyl ether, helothane). However, reversal of the effects of other volatile agents (ethanol, butanol), sodium pentobarbitone and two local anaesthetic agents (procaine, dibucaine) did not occur. The pressures used to effect a reversal were less than anticipated. This apparent inconsistency with the critical volume hypothesis for anaesthesia is discussed.