title: Intraoperative monitoring of myogenic motor-evoked potentials from the external anal sphincter muscle to transcranial electrical stimulation.
abstract: METHODS
  Motor-evoked potentials from the external anal sphincter were analyzed using transcranial electrical stimulation during spinal surgery in patients under general anesthesia.
  
  
  OBJECTIVE
  To investigate whether motor-evoked potentials from the external anal sphincter could be elicited by transcranial electrical stimulation under general anesthesia.
  
  
  BACKGROUND
  Lumbosacral surgery often places nerve rootlets at risk for injury during operative dissection. Specifically, injury for sacral rootlets can result in bowel and bladder dysfunction, but the techniques for monitoring bowel and bladder function are limited.
  
  
  METHODS
  Thirty patients who underwent elective spinal surgery were studied. Patients were anesthetized with 50% nitrous oxide in oxygen, fentanyl, and 4 mg/kg/h of propofol (n = 19) or 1 mg/kg/h of ketamine (n = 11). The level of neuromuscular blockade, assessed by recording the M-response from the right abductor pollicis brevis muscle, was maintained at an M-response amplitude of 40-50% of control. Motor-evoked potentials in response to a multipulse transcranial electrical stimulation at stimulus sites of C3-C4 or Fz-Cz were recorded from the skin over the subcutaneous part of the external anal sphincter using a plug-type electrode probe. The success rate of motor-evoked potentials' recording and peak-to-peak amplitude and the onset latency of motor-evoked potentials were evaluated.
  
  
  RESULTS
  Success rates of motor-evoked potentials from the external anal sphincter were 73% and 53% after transcranial stimulation at stimulus sites of C3-C4 and Cz-Fz, respectively. Amplitudes of motor-evoked potentials after C3-C4 stimulation were significantly greater than those after Cz-Fz stimulation. Motor-evoked potential latency from the external anal sphincter was 18.6 +/- 1.5 and 19.0 +/- 2.7 msec after C3-C4 and Cz-Fz stimulation, respectively.
  
  
  CONCLUSIONS
  The results suggest that, using a transcranial multipulse stimulation, monitoring of motor-evoked potentials from the external anal sphincter is feasible during ketamine- and propofol-based anesthesia. However, further improvement of techniques would be required for intraoperative elicitation of motor-evoked potentials from the external anal sphincter.
authors.affiliation: Department of Anesthesiology, Nara Medical University, Kashihara, Nara, Japan. seninoue@nmu-gw.naramed-u.ac.jp
authors.forename: Satoki
authors.initials: S
authors.lastname: Inoue
authors.forename: Masahiko
authors.initials: M
authors.lastname: Kawaguchi
authors.forename: Shimoda
authors.initials: S
authors.lastname: Takashi
authors.forename: Meiko
authors.initials: M
authors.lastname: Kakimoto
authors.forename: Takanori
authors.initials: T
authors.lastname: Sakamoto
authors.forename: Katsuyasu
authors.initials: K
authors.lastname: Kitaguchi
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Furuya
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Morimoto
authors.forename: Toshisuke
authors.initials: T
authors.lastname: Sakaki
mesh_terms: D000293:Adolescent; D000328:Adult; D001003:Anal Canal / Q000294:innervation / Q000502:physiology*; D000758:Anesthesia; D001921:Brain / Q000502:physiology; D004558:Electric Stimulation / Q000379:methods; D019054:Evoked Potentials, Motor / Q000502:physiology*; D005260:Female; D006801:Humans; D007649:Ketamine / Q000008:administration & dosage; D008297:Male; D008875:Middle Aged; D016343:Monitoring, Intraoperative / Q000295:instrumentation / Q000379:methods*; D018482:Muscle, Skeletal / Q000294:innervation / Q000502:physiology; D015742:Propofol / Q000008:administration & dosage; D011930:Reaction Time / Q000502:physiology; D013122:Spinal Diseases / Q000601:surgery*
chemical_list: D007649:Ketamine; D015742:Propofol