Ubags L H, Kalkman C J, Been H D
Department of Anesthesiology, Academic Hospital, University of Amsterdam, The Netherlands.
Neurosurgery. 1998 Jul;43(1):90-4; discussion 94-5. doi: 10.1097/00006123-199807000-00058.
Transcranial motor evoked potentials (tc-MEPs) are used to monitor the spinal cord intraoperatively. Volatile anesthetics considerably depress amplitudes of tc-MEPs. This study was undertaken to determine whether multipulse stimulation might overcome this depressant effect.
In 10 patients undergoing spinal surgery, incremental doses of isoflurane were added to a nitrous oxide/opioid anesthetic regimen and maintained constant at 0.2, 0.4, and 0.6% end tidal for at least 15 minutes. tc-MEP responses to single-pulse and trains of three and five (interstimulus interval, 2 ms) transcranial electrical stimuli were recorded from the tibialis anterior muscles.
Before the addition of isoflurane, tc-MEPs were recordable in all patients, even with single-pulse stimuli (median amplitude, 428 microV). With 0.2% end-tidal isoflurane, tc-MEPs were recordable in eight patients with single-pulse stimulation and in all patients with three and five successive stimuli. At 0.4% isoflurane, responses were recordable in only one patient using single-pulse stimuli and in all patients using three and five stimuli. With 0.6% isoflurane, tc-MEPs to trains of three and five stimuli were recordable in all patients except one. The amplitude of the responses obtained with 0.2, 0.4, and 0.6% end-tidal isoflurane was significantly smaller than that of control responses (P < 0.05).
These data suggest that despite the powerful depressant effects of isoflurane on myogenic motor responses, tc-MEP monitoring during isoflurane anesthesia may be feasible, provided that multipulse stimulation paradigms are used and the concentration of isoflurane does not exceed 1 minimal anesthetic concentration unit.
经颅运动诱发电位（tc-MEPs）用于术中监测脊髓。挥发性麻醉药会显著降低tc-MEPs的波幅。本研究旨在确定多脉冲刺激是否可以克服这种抑制作用。
10例接受脊柱手术的患者，在氧化亚氮/阿片类麻醉方案基础上，递增异氟烷剂量，并在呼气末浓度分别维持在0.2%、0.4%和0.6%至少15分钟。记录胫前肌对单脉冲以及三个和五个（刺激间隔2毫秒）经颅电刺激的tc-MEP反应。
在添加异氟烷之前，所有患者即使采用单脉冲刺激也可记录到tc-MEPs（中位波幅，428微伏）。呼气末异氟烷浓度为0.2%时，8例患者采用单脉冲刺激可记录到tc-MEPs，所有患者采用三个和五个连续刺激均可记录到。异氟烷浓度为0.4%时，仅1例患者采用单脉冲刺激可记录到反应，所有患者采用三个和五个刺激均可记录到。异氟烷浓度为0.6%时，除1例患者外，所有患者采用三个和五个刺激的tc-MEPs均可记录到。呼气末异氟烷浓度为0.2%、0.4%和0.6%时获得的反应波幅显著小于对照反应（P<0.05）。
这些数据表明，尽管异氟烷对肌源性运动反应有强大的抑制作用，但在异氟烷麻醉期间进行tc-MEP监测可能是可行的，前提是采用多脉冲刺激模式且异氟烷浓度不超过1个最低麻醉浓度单位。
