Modified transcranial electromagnetic motor evoked potential obtained with train-of-four monitor for scoliosis surgery.
BACKGROUND
To monitor the spinal cord with somatosensory evoked potential (SSEP) is an accepted adjunct in the surgical correction of spinal deformities, but it does not directly assess the motor function. The use of motor evoked potential (MEP) has thus been introduced in an effort to meet this important need.


METHODS
This preliminary report concerned 30 cases of scoliosis who underwent surgical correction under the surveillance of modified transcranial electromagnetic motor evoked potential (tcMMEP). Train-of four (TOF) stimulator output was connected to an electromagnetic stimulator. The rate of repetition and interval of stimulation were controlled by TOF stimulator. Electromyographic (EMG) signals were obtained from the abductor hallucis muscle of both feet and interpreted as MEP activity. Anesthesia was made possible by propofol as a basic agent and isoflurane as supplement. Analgesia was obtained with sufentanil and fentanyl and amnesia enhanced by midazolam. Atracurium mixed with vecuronium in a ratio of 4:1 by weight in possible lowest dose was given to provide adequate muscle relaxation yet without the molestation of rapid reversal upon the request of wake-up test by the surgeon. Deliberate hypothermia and controlled hypotension were also applied since they did not interfere with the tcMMEP signals.


RESULTS
Although no attempt was made to control the level of muscle relaxation at T1 more than 30%, tcMMEP signals could be obtainable during induction, at the time of surgical correction and at the end of the operation. TcMMEP onset latency was 27.32 +/- 0.45 msec on the left side and 27.27 +/- 0.54 msec on the right side. The amplitude was 3.52 +/- 1.97 mV on the left side and 4.05 +/- 1.22 mV on the right side.


CONCLUSIONS
The modified tcMMEP is so stable and convincing that research for similar modification is now undergoing with the other brand of TOF monitor by our team.
Department of Anesthesiology, Tzu-Chi General Hospital, Hualien, Taiwan, R.O.C.
B C
BC
Lin
I H
IH
Chen
D000293:Adolescent; D000328:Adult; D002648:Child; D004576:Electromyography; D019054:Evoked Potentials, Motor; D005260:Female; D006801:Humans; D008280:Magnetics; D008297:Male; D008875:Middle Aged; D011930:Reaction Time; D012600:Scoliosis / Q000503:physiopathology / Q000601:surgery*