title: Optimal placement of recording electrodes for quantifying facial nerve compound muscle action potential.
abstract: OBJECTIVE
  To analyze optimal placement of recording-needle electrodes surrounding the eye and lip for facial nerve monitoring by identifying the maximum compound muscle action potential (CMAP) recorded by electrode pairs of different spatial configurations.
  
  
  METHODS
  Prospective clinical trial.
  
  
  METHODS
  Ambulatory surgery at a tertiary care center.
  
  
  METHODS
  Thirty adults undergoing chronic ear surgery such as tympanoplasty, mastoidectomy, ossicular chain reconstruction, stapedectomy, and cochlear implantation.
  
  
  METHODS
  Facial nerve monitoring.
  
  
  METHODS
  Suprathreshold (threshold + 0.2 V) CMAP responses are recorded from referential paired needle electrodes placed into orbicularis oculi (1.5-cm spacing; n = 15) and orbicularis oris (1.0-cm spacing; n = 15) muscles. Optimal recording electrode placement is inferred by identifying the maximum evoked CMAP amplitude.
  
  
  RESULTS
  For the eye, placement of electrodes by the orbital rim and into the upper eyelid is significantly better (Friedman test; p < 0.01) than the other 2 configurations. For the lip, placement of electrodes into the oral commissure and either the upper or lower lip is satisfactory because there is no statistically significant difference among the configurations (Friedman test; p > 0.2).
  
  
  CONCLUSIONS
  Recording electrode placement configurations that capture the largest CMAP responses are recommended as standard operating procedure for intraoperative facial nerve monitoring.
authors.affiliation: Neurophysiological Monitoring Service, University of California, San Francisco, California 94143-0112, USA. lanjun.guo@ucsfmedctr.org
authors.forename: LanJun
authors.initials: L
authors.lastname: Guo
authors.forename: Paul
authors.initials: P
authors.lastname: Jasiukaitis
authors.forename: Lawrence H
authors.initials: LH
authors.lastname: Pitts
authors.forename: Steven W
authors.initials: SW
authors.lastname: Cheung
mesh_terms: D000200:Action Potentials / Q000502:physiology*; D000328:Adult; D000368:Aged; D001309:Auditory Threshold / Q000502:physiology; D019929:Cochlear Implantation; D004566:Electrodes; D004576:Electromyography / Q000295:instrumentation; D005154:Facial Nerve / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D016343:Monitoring, Intraoperative; D018482:Muscle, Skeletal / Q000294:innervation*; D009998:Ossicular Prosthesis; D011446:Prospective Studies; D013201:Stapes Surgery; D014433:Tympanoplasty