Preservation of neurogenic motor-evoked potentials during isoflurane electroencephalographic burst suppression in rats.

Abstract

A prospective laboratory study was performed in a rat model. To test the hypothesis that neurogenic motor-evoked potentials are more resistant to suppressive changes from the volatile anesthetic isoflurane than cortically recorded somatosensory-evoked potentials and electroencephalography. Techniques for monitoring spinal cord motor tracts have been developed because sensory tract monitoring with somatosensory-evoked potentials is at times inadequate. Potentials from transcranial magnetic and electrical stimulation are very sensitive to anesthesia. Neurogenic motor-evoked potentials are thought to be more resistant. Eight mature Sprague-Dawley rats were studied during isoflurane general anesthesia. Two-channel raw and computer-processed electroencephalograms, somatosensory-evoked potentials, and neurogenic motor-evoked potentials were recorded at six levels of anesthetic depths. Neurogenic motor-evoked potential amplitudes and latencies were unaltered. The electroencephalograms were depressed to isoelectricity with periodic burst activity above 1.27% isoflurane. Processed electroencephalograms showed depression above 0.72%. The somatosensory-evoked potentials were suppressed by increasing isoflurane and were not discernible at 2.2%. Neurogenic motor-evoked potential signals are well preserved in rats during exposure to isoflurane concentrations that eliminate somatosensory-evoked potential waveforms and depress electroencephalograms to burst suppression.