Dependence of halothane potency on pH.

The effect of halothane on the amplitude and conduction time of the evoked nerve action potential of a mammalian nerve preparation was determined in vitro. The action of 4 per cent v/v halothane on the action potential was measured at three different hydrogen ion concentrations in the Krebs perfusate, namely, pH 6.57, pH 7.40, pH 8.00. Halothane potency, assessed by the depression of the action potential amplitude, was inversely proportional to the extracellular pH and represented a mean 18.7 per cent decrease of halothane potency for a rise of one pH unit. The change in nerve conduction time induced by halothane was found to be less with a high extracellular pH than with a normal pH, and represented an 18.8 per cent decrease in halothane potency for a rise of one pH unit.