Transcranial motor-evoked potentials of laryngeal muscles for intraoperative neuromonitoring of the vagus nerve during thyroid surgery

  • Takashi Ichino
  • Satoshi TanakaEmail author
  • Ryusuke Tanaka
  • Naruaki Tanaka
  • Takashi Ishida
  • Yuki Sugiyama
  • Mikito Kawamata
Original Article



The aim of this study was to elucidate normative features of vagal motor-evoked potentials (MEPs) induced by transcranial electrical stimulation (TES) and to determine the influence of functional decline of the recurrent laryngeal nerve (RLN) on vagal MEPs during thyroid surgery.


A total of 54 patients undergoing elective thyroid surgery under general anesthesia were enrolled in this study. Vagal MEPs induced by TES were measured from the vocal cord using one of two types of electrodes (wire type or wide and flat type) mounted on an endotracheal tube. We investigated the effects of stimulation intensity and train pulse number on vagal MEP amplitude, the time course of vagal MEP amplitude during surgery, and the effects of functional decline of the RLN on vagal MEPs.


The success rate of vagal MEP monitoring with wide- and flat-type electrodes was significantly higher than that with wire-type electrodes. Reliable vagal MEPs were obtained at a stimulation intensity of approximately 300 V with 3 or more pulses in 91% of the patients without preoperative RLN palsy (RLNP), and the amplitude was augmented with increasing stimulation intensity and train pulse number. Vagal MEP amplitude decreased during thyroid surgery and then partially recovered at the end of surgery. Vagal MEP amplitude recorded from the electrode ipsilateral to preoperative RLNP was significantly lower than that on the contralateral intact side.


Vagal MEPs induced by TES can be obtained with a high success rate during thyroid surgery and would reflect functional status of the RLN.


Vagus nerve Motor-evoked potential Electromyographic endotracheal tube Transcranial electrical stimulation Recurrent laryngeal nerve palsy 


Compliance with ethical standards

Conflict of interest

The present research was supported solely by hospital and department sources. None of the authors have any financial interests in products related to this study.


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Copyright information

© Japanese Society of Anesthesiologists 2019

Authors and Affiliations

  • Takashi Ichino
    • 1
  • Satoshi Tanaka
    • 1
    Email author
  • Ryusuke Tanaka
    • 1
  • Naruaki Tanaka
    • 1
  • Takashi Ishida
    • 1
  • Yuki Sugiyama
    • 1
  • Mikito Kawamata
    • 1
  1. 1.Department of Anesthesiology and ResuscitologyShinshu University School of MedicineMatsumotoJapan

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