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October 13, 2007
9:00 AM - 10:30 PM
Room Room 301
Somatosensory and Motor Evoked Potentials during Sevoflurane and Propofol Anesthesia
Michael S. Kincaid, M.D., Michael J. Souter, M.D., Patrick D. Bryan, Mark Klein, Arthur M. Lam, M.D.
Anesthesiology, University of Washington, Seattle, Washington
Background and Purpose: Transcranial electrical motor evoked potentials (MEP) have joined somatosensory evoked potentials (SSEP) as an important aspect of neurophysiologic monitoring during both intracranial and spine surgery. General anesthesia is known to diminish the quality of signals with SSEP, decreasing amplitude and increasing latency, with volatile anesthesia having a greater effect than intravenous anesthesia. There is little quantitative information on the comparative effect of volatile and intravenous anesthetics on MEP signal quality, however. The purpose of this study is to describe the effects of propofol and sevoflurane on SSEP and MEP in patients undergoing both spine and neurosurgical procedures.

Methods: Following IRB approval, we prospectively collected data on patients undergoing surgery in which monitoring of both MEP and SSEP was requested. Baseline MEP and SSEP, as well as mean arterial pressure (MAP) and patient temperature were recorded during stable sevoflurane and opioid anesthesia. The subjects were then transitioned to propofol and opioid anesthesia. Following a time lapse of greater than one hour to allow for steady state conditions, MEP and SSEP were again recorded. MEP, SSEP, and physiologic parameters were then compared using a paired t-test.

All data are presented as mean ± SD.

Results: 15 subjects (5 men, 10 women), age 50 ± 15 years, were included in this analysis. During sevoflurane anesthesia, end-tidal concentration was 1.3% ± 0.3, while the infusion rate during propofol anesthesia was 147 mcg/kg/min ± 36. From discontinuation of sevoflurane to recording of signals on propofol anesthesia, 1 hour 58 minutes ± 22 minutes elapsed. Temperature and MAP were unchanged (Temp: 35.6 ± 0.86 vs. 35.4 ± 0.94, p = 0.49; MAP: 76 ± 7 vs. 75 ± 5, p = 0.35). SSEP amplitudes in the upper and lower extremities were unchanged by the switch from volatile to intravenous anesthesia (N20-P25: 2.0 ± 1.4 vs. 2.2 ± 1.9, p = 0.25; N33-P37: 0.80 ± 0.64 vs. 0.80 ± 0.68, p = 0.97). Both upper and lower extremity MEP improved with propofol anesthesia, however (UE: 192 ± 217 vs. 1716 ± 1731, p = 0.003; LE: 100 ± 174 vs. 886 ± 1247, p = 0.017).

Conclusion: Although propofol anesthesia has little benefit over sevoflurane anesthesia while performing SSEP monitoring, it does offer substantial benefit when MEP monitoring is needed, with nearly a 9 fold increase in amplitude two hours after discontinuation of sevoflurane. This study is limited by the absence of a study arm in which subjects receive propofol anesthesia prior to sevoflurane, which would help eliminate the bias engendered by time-related decline in signal quality under anesthesia. Given the significant improvement in MEP in this study with propofol, despite the passage of time, it is unlikely that such a group of subjects would add clinically relevant information, however.[table1]

Anesthesiology 2007; 107: A1
Somatosensory and Motor Evoked Potentials
Sevoflurane2.0 ± 1.40.80 ± 0.64192 ± 217100 ± 174
Propofol2.2 ± 1.90.80 ± 0.681716 ± 1731886 ± 1247
UE = Upper Extremity, LE = Lower Extremity