The Influence Of Volatile Anesthetics Sevoflurane And Isoflurane On Motor Evoked Potential Of The Forearm Muscle

Objective：With index of the latency and amplitude of motor evoked potential， toinvestigate the influence of volatile anesthetics sevoflurane and isoflurane on MotorEvoked Potential of the forearm muscle，provide some information for Motionevoked potential monitoring．Methods： thirty-seven ASA I-II patients aged45-65years old undergoingneurosurgery operation under general anesthesia were randomly divided into2groups：sevoflurane group (group I，n=18) and isoflurane (group II，n=19). Thepatients were infused midazolam0.05mg/kg before induction of anaesthesia in bothgroups.Group I (sevoflurane group) induced with sevoflurane administered byup-and-down，The patients breathed sevoflurane until the predetermined targetend-tidal sevoflurane concentration was reached for15min. The initial end-tidalconcentration of sevoflurane was set at2.8%. If the latency and amplitude of motorevoked potential disappear，the end-tidal concentration of sevoflurane was decreasedby0.4%，while if not，increased by0.4%;GroupII (isoflurane group) induced withisoflurane administered by up-and-down，The patients breathed isoflurane until the predetermined target end-tidal isoflurane concentration was reached for15min.The initial end-tidal concentration of isoflurane was set at2.0%．If the latencyand amplitude of motor evoked potential disappear，the end-tidal concentration ofisoflurane was decreased by0.4%，while if not，increased by0.4%. Every5minutesto record the patients’ abductor pollicis brevi muscle of the amplitude and latency ofmotor evoked potentials (MEP)，mean arterial pressure (MAP)， heart rate (HR)，and pulse oxygen saturation (SpO2)，and Breathe out at the end of the CO2partialpressure (ETCO2)， The median effective dose (the latency and amplitude of motorevoked potential disappear)and its95%confidence interval of sevoflurane andisoflurane were calculated.Results：(1) ED50of sevoflurane in group I is2.35%or1.39MAC(minimum alveolarconcentration),and its95%confidence interval is2.21%~2.50%or1.31MAC~1.47MAC;(2) ED50of isoflurane in group II is1.59%or1.38MAC(minimum alveolarconcentration),and its95%confidenceinterval is1.50%~1.67%or1.30MAC~1.45MAC．(3) When the end-tidal sevoflurane concentration was2.0%, the success rate of MEPwas100%;When the end-tidal sevoflurane concentration was24%, the success rateof MEP was33%;When the end-tidal sevoflurane concentration was2.8%, thesuccess rate of MEP was0.(4) When the end-tidal isoflurane concentration was1.2%, the success rate of MEPwas100%;When the end-tidal isoflurane concentration was1.6%, the success rate ofMEP was44%;When the end-tidal isoflurane concentration was2.0%, the successrate of MEP was0.Conclusion：When motion evoked potential monitoring is implemented，(1)Application of sevoflurane anesthesia alone, when motion evoked potentialmonitoring success, its ED50is2.35%or1.39MAC，and its95%confidence interval is2.21%-2.50%， or1.31MAC-1.47MAC;(2)Application of isoflurane anesthesia alone, when motion evoked potentialmonitoring success, its ED50is1.59%or1.38MAC， and its95%confidenceinterval is1.50%-1.67%or1.30MAC-1.45MAC;(3)Sevoflurane can restrain the upper limbs motion evoked potential (MEP), theeffects are dose dependent;(4)Isoflurane can restrain the upper limbs motion evoked potential (MEP), theeffects are dose dependent．...