Temperature‐Dependent Nerve‐Blocking Action of Lidocaine and Halothane

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Abstract
The effect of lidocaine and halothane on the compound action potential of rat sciatic nerves was studied under hypo- and hyperthermic conditions. In drug-free desheathed nerves, a total but reversible cold block occurred at 10-11.degree. C, and an irreversible heat block at 46.degree. C. Cooling potentiated the dose-dependent blocking action of lidocaine (decreased amplitude, and increased duration and latency of the compound action potential). Total block of conduction occurred at 17.degree. C with 100 .mu.M lidocaine, at 20.degree. C with 200 .mu.M lidocaine and at 24.degree. C with 400 .mu.M lidocaine. In nerves equilibrated in 200 .mu.M lidocaine solution, the lidocaine concentrations in the nerves decreased as the temperature decreased; at 20.degree. C, the lidocaine concentration was .apprx. half of that at 37.degree. C. The nerve-blocking effect of lidocaine was potentiated by increasing the temperature > 37.degree. C. At 30.degree. C and 20.degree. C, 1 vol. % halothane caused a slight time-dependent inhibition of the compound action potential. When the nerves were exposed to 2.5 vol. % halothane, the decrease in amplitude and increase in duration and latency were potentiated by hypothermia and were time dependent. Interaction of halothane and temperature of 40.degree. C was insignificant. Thermodynamic principles suggest similarities between high pressure and cooling in reversing anesthesia; cooling potentiated the anaesthetic effect of lidocaine and halothane in this study. Temperature may be an interesting physical variable in studying nerve-blocking mechanisms.

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