THE EFFECTS OF PROPOFOL ON RAT TRANSCRANIAL MAGNETIC MOTOR EVOKED-POTENTIALS

INTRAOPERATIVE MONITORING OF motor evoked potentials (MEPs) may become a valuable test of spinal cord function during surgery. Unfortunately , MEP responses are affected by most common anesthetics. We studied th e effect of intravenous propofol on transcranial magnetic MEPs (tcMMEP s) in the rat. Baseline tcMMEPs were recorded before administration of the drug. Each rat then received three induction doses of propofol, 1 0, 5, and 5 mg/kg (totaling 10, 15, and 20 mg/kg) and three successive 20-minute infusion doses at rates of 10, 20, and 40 mg/kg/h, respecti vely. An MEP intensity series was performed after each induction dose, during: each infusion, and during a 20-minute recovery period. tcMMEP s recorded during the induction period demonstrated a significant, dos e-dependent increase in onset latency and a marked decrease in amplitu de. Infusion tcMMEPs displayed increased onset latencies but demonstra ted a significant change in amplitudes only after the largest infusion dose. The MEPs approached baseline levels after discontinuation of th e propofol. This study demonstrates that tcMMEPs can be successfully r ecorded from the rat during propofol anesthesia.