title: Transoesophageal spinal cord stimulation for motor-evoked potentials monitoring: feasibility, safety and stability.
abstract: OBJECTIVE
  Specificity of transcranial motor-evoked potentials (MEPs) is low because amplitude fluctuation is common, which seems due to several technical and fundamental reasons including difficulty in electrodes positioning and fixation for transcranial stimulation and susceptibility to anaesthesia. This study aimed to investigate the feasibility, safety and stability of our novel technique of transoesophageal spinal cord stimulation to improve the stability of MEPs.
  
  
  METHODS
  Ten anaesthetized adult beagle dogs were used. Transoesophageal stimulation was performed between the oesophageal luminal surface electrode (cathode) and a subcutaneous needle electrode (anode) at the fourth to fifth thoracic vertebra level. Stimulation was achieved with a train of five pulses delivered at 2.0-ms intervals. Compound muscle action potentials were recorded from four limbs and external anal sphincter muscles. Stability to anaesthetic agents was tested at varying speeds of propofol and remifentanil, and effects of varying concentration of sevoflurane inhalation were also evaluated.
  
  
  RESULTS
  Transoesophageal MEPs could be recorded without difficulty in all dogs. Fluoroscopic evaluation showed that electrodes misalignment up to 5 cm cranially or caudally could be tolerated. Stimulus intensity to achieve maximum amplitude of hindlimb muscle potentials on both sides was significantly lower by transoesophageal stimulation than by transcranial stimulation (383 ± 41 vs 533 ± 121 V, P = 0.02) and had less interindividual variability. Latency of transoesophageal MEPs was shorter than that of transcranial MEPs at every recording point. No arrhythmia was provoked during stimulation. Animals that were allowed to recover showed no neurological abnormality. In the two sacrificed animals, the explanted oesophagus showed no mucosal injury. Stability to varying dose of anaesthetic agents was similar between transoesophageal and transcranial stimulation, except for the potentials of forelimbs by transoesophageal stimulation that were resistant to anaesthetic depression.
  
  
  CONCLUSIONS
  Transoesophageal stimulation for MEPs monitoring was feasible without difficulty and safe. Although its stability to anaesthetic agents was similar to that of transcranial stimulation, its technical ease and small interindividual variability warrants further studies on the response to spinal cord ischaemia.
authors.affiliation: First Department of Surgery, Hamamatsu University School of Medicine, Hamamatsu, Japan.
authors.forename: Kazumasa
authors.initials: K
authors.lastname: Tsuda
authors.affiliation: First Department of Surgery, Hamamatsu University School of Medicine, Hamamatsu, Japan shiyanor@hama-med.ac.jp.
authors.forename: Norihiko
authors.initials: N
authors.lastname: Shiiya
authors.affiliation: First Department of Surgery, Hamamatsu University School of Medicine, Hamamatsu, Japan.
authors.forename: Daisuke
authors.initials: D
authors.lastname: Takahashi
authors.affiliation: First Department of Surgery, Hamamatsu University School of Medicine, Hamamatsu, Japan.
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Ohkura
authors.affiliation: First Department of Surgery, Hamamatsu University School of Medicine, Hamamatsu, Japan.
authors.forename: Katsushi
authors.initials: K
authors.lastname: Yamashita
authors.affiliation: First Department of Surgery, Hamamatsu University School of Medicine, Hamamatsu, Japan.
authors.forename: Yumi
authors.initials: Y
authors.lastname: Kando
mesh_terms: D018681:Anesthetics, General / Q000494:pharmacology; D000818:Animals; D004195:Disease Models, Animal; D004285:Dogs; D004305:Dose-Response Relationship, Drug; D004947:Esophagus; D019054:Evoked Potentials, Motor / Q000187:drug effects / Q000502:physiology*; D005240:Feasibility Studies; D016343:Monitoring, Intraoperative / Q000009:adverse effects / Q000379:methods*; D020760:Spinal Cord Ischemia / Q000175:diagnosis / Q000517:prevention & control; D062187:Spinal Cord Stimulation / Q000009:adverse effects / Q000379:methods*
chemical_list: D018681:Anesthetics, General
keywords: Anaesthesia; Aortic surgery; Motor-evoked potentials; Oesophageal electrode; Spinal cord ischaemia