Electrical stimulation as a substitute for the tail clamp in the determination of minimum alveolar concentration

Circumstances may preclude the use of standard stimuli, namely tail clamp or surgical incision, to determine minimum alveolar concentration. In rats anesthesized with isoflurane, an alternative stimulus, electrical currents (10, 15, 20, or 40 V; biphasic pulses of 6.5 ms duration; 50 Hz), gave results comparable to those obtained with the tail clamp and the results did not change with repeated measurements if care was taken to avoid desensitization by exhaustion of a particular set of electrodes. The 40 V stimulation gave slightly higher values (4%; P < 0.006) than tail clamp, but the difference was too small to be of experimental significance. More importantly, the higher voltages produced desensitization after fewer attempts at stimulation. In addition to these results with isoflurane, we found that 15 V stimulation and tail clamp produced comparable minimum alveolar concentration values for halothane and for desflurane.