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.
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.
Department of Orthopedics, Kyushu Rosai Hospital, Kitakyushu, Japan. teru0805leo@yahoo.co.jp
Yoshiteru
Y
Shida
Chikami
C
Shida
Norihiko
N
Hiratsuka
Kozo
K
Kaji
Junichi
J
Ogata
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D018685:Anesthetics, Inhalation / Q000494:pharmacology*; D018686:Anesthetics, Intravenous / Q000494:pharmacology; D019054:Evoked Potentials, Motor / Q000187:drug effects*; D005121:Extremities; D005260:Female; D006801:Humans; D035002:Lower Extremity; D008297:Male; D008738:Methyl Ethers / Q000494:pharmacology*; D008875:Middle Aged; D016343:Monitoring, Intraoperative / Q000379:methods; D015742:Propofol / Q000494:pharmacology; D011446:Prospective Studies; D000077149:Sevoflurane; D013131:Spine / Q000601:surgery*; D050781:Transcranial Magnetic Stimulation / Q000379:methods*; D034941:Upper Extremity
D018685:Anesthetics, Inhalation; D018686:Anesthetics, Intravenous; D008738:Methyl Ethers; D000077149:Sevoflurane; D015742:Propofol