title: A new criterion for the alarm point for compound muscle action potentials.
abstract: OBJECTIVE
  The purpose of this study was to review the present criteria for the compound muscle action potential (CMAP) alert and for safe spinal surgery.
  
  
  METHODS
  The authors conducted a retrospective study of 295 patients in whom spinal cord monitoring had been performed during spinal surgery. The waveforms observed during spinal surgery were divided into the following 4 grades: Grade 0, normal; Grade 1, amplitude decrease of 50% or more and latency delay of 10% or more; Grade 2, multiphase pattern; and Grade 3, loss of amplitude. Waveform grading, its relationship with postoperative motor deficit, and CMAP sensitivity and specificity were analyzed. Whenever any wave abnormality occurred, the surgeon was notified and the surgical procedures were temporarily suspended. If no improvements were seen, the surgery was terminated.
  
  
  RESULTS
  Compound muscle action potential wave changes occurred in 38.6% of cases. With Grade 1 or 2 changes, no paresis was detected. Postoperative motor deficits were seen in 8 patients, all with Grade 3 waveform changes. Among the 287 patients without postoperative motor deficits, CMAP changes were not seen in 181, with a specificity of 63%. The false-positive rate was 37% (106 of 287). However, when a Grade 2 change was set as the alarm point, sensitivity was 100% and specificity was 79.4%. The false-positive rate was 20% (59 of 295).
  
  
  CONCLUSIONS
  Neither the Grade 1 nor the Grade 2 groups included patients who demonstrated a motor deficit. All pareses occurred in cases showing a Grade 3 change. Therefore, the authors propose a Grade 2 change (multiphasic waveform) as a new alarm point. With the application of this criterion, the false-positive rate can be reduced to 20%.
authors.affiliation: Department of Orthopedic Surgery, Nagoya University School of Medicine, Aichi 466-8550, Japan. z.ito@nifty.com
authors.forename: Zenya
authors.initials: Z
authors.lastname: Ito
authors.forename: Shiro
authors.initials: S
authors.lastname: Imagama
authors.forename: Yoshihito
authors.initials: Y
authors.lastname: Sakai
authors.forename: Yoshito
authors.initials: Y
authors.lastname: Katayama
authors.forename: Norimitsu
authors.initials: N
authors.lastname: Wakao
authors.forename: Kei
authors.initials: K
authors.lastname: Ando
authors.forename: Kenichi
authors.initials: K
authors.lastname: Hirano
authors.forename: Ryoji
authors.initials: R
authors.lastname: Tauchi
authors.forename: Akio
authors.initials: A
authors.lastname: Muramoto
authors.forename: Hany
authors.initials: H
authors.lastname: El Zahlawy
authors.forename: Yukihiro
authors.initials: Y
authors.lastname: Matsuyama
authors.forename: Naoki
authors.initials: N
authors.lastname: Ishiguro
mesh_terms: D000200:Action Potentials / Q000502:physiology*; D000328:Adult; D004558:Electric Stimulation; D004576:Electromyography; D019054:Evoked Potentials, Motor / Q000502:physiology; D005073:Evoked Potentials, Somatosensory / Q000502:physiology; D005260:Female; D006801:Humans; D008297:Male; D016343:Monitoring, Intraoperative / Q000379:methods*; D018482:Muscle, Skeletal / Q000502:physiology*; D019635:Neurosurgical Procedures / Q000379:methods*; D012189:Retrospective Studies; D013116:Spinal Cord / Q000502:physiology / Q000601:surgery*; D013131:Spine / Q000601:surgery*