General anesthetic effects on compound muscle action potentials elicited by single or dual spinal cord stimulation

The aim of this study was to determine the optimal conditions, during general anesthesia, to obtain reproducible monitoring of compound muscle action potentials (CMAPs) as a means to evaluate motor tract integrity. The CMAPs were recorded in the soleus muscle of cats and were elicited by either single or double pulse stimulations (with various amplitudes and interpulse durations) of the spinal cord via an epidural electrode. The effects of various depths of general anesthesia with halothane, enflurane, isoflurane, or propofol on such recordings were also determined. For each agent, the CMAP amplitudes were significantly greater following double pulse stimulations (2-ms optimal interpulse duration) relative to single pulses. The CMAP amplitudes elicited by double pulse stimulations were the same at propofol concentrations of 50, 100, 150, and 200 micrograms/kg/min, whereas those for each volatile anesthetic, at all concentrations studied (0.5%, 1.0%, 1.5%, or 2.0%), were significantly lower. It was concluded that to obtain reliable CMAP amplitudes, general anesthesia with propofol should be employed and the potentials should be evoked by double pulse stimulations.