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High-frequency Stimulation Restored Motor-evoked Potentials to the Baseline Level in the Upper Extremities but Not in the Lower Extremities Under Sevoflurane Anesthesia in Spine Surgery

Shida, Yoshiteru MD*; Shida, Chikami MD; Hiratsuka, Norihiko MD*; Kaji, Kozo MD*; Ogata, Junichi MD, PhD

Journal of Neurosurgical Anesthesiology: April 2012 - Volume 24 - Issue 2 - p 113–120
doi: 10.1097/ANA.0b013e318237fa41
Clinical Investigations

Background: Volatile anesthetics attenuate medium-frequency (250 to 500 Hz) pulse train transcranial electrical stimulation (TES) motor-evoked potentials (MEPs) better than propofol. High-frequency (1000 Hz) TES may restore hand MEP amplitude under volatile anesthesia, but its effect on leg MEPs critical for spine surgery monitoring is unknown.

Methods: The effects of sevoflurane and propofol and modulation of the stimulation frequencies on MEPs elicited by TES in the anterior tibial, abductor hallucis, and abductor pollicic brevis muscles were investigated in 31 patients undergoing spine surgery. MEPs elicited by transcranial magnetic stimulation were also obtained before the surgeries and compared with the TES MEPs.

Results: Sevoflurane attenuated the MEP amplitudes significantly. The MEP amplitudes increased with the TES frequency in the case of the arms, but not the legs, under sevoflurane anesthesia. The MEPs recorded under propofol anesthesia did not differ from those elicited by transcranial magnetic stimulation before the surgery (control).

Conclusions: Sevoflurane is inadvisable for MEP monitoring in the legs during spine surgery as modulation of the TES frequency did not eliminate the suppressive effect of sevoflurane on the MEPs in the legs. Clinicians should be forewarned of the greater risk of unmonitorable MEPs, especially in the legs, under sevoflurane anesthesia.

Departments of *Orthopedics

Anesthesiology, Kyushu Rosai Hospital, Kitakyushu, Japan

The authors have no funding or conflicts of interest to disclose.

Reprints: Yoshiteru Shida, MD, Department of Orthopedics, Sasebo Kyosai Hospital, 10-17 Shimanji, Sasebo, Nagasaki 857-8575, Japan (e-mail:

Received July 2, 2011

Accepted September 15, 2011

© 2012 Lippincott Williams & Wilkins, Inc.