title: The vagus nerve, recurrent laryngeal nerve, and external branch of the superior laryngeal nerve have unique latencies allowing for intraoperative documentation of intact neural function during thyroid surgery.
abstract: OBJECTIVE
  To define normative amplitude and latency of vagus, recurrent laryngeal nerve (RLN), and external branch of superior laryngeal nerve (EBSLN) and to apply them to postoperative neural function documentation. To our knowledge, this is the first study to report electrophysiologic characteristics of all three nerves in a consecutive patient series.
  
  
  METHODS
  Prospective.
  
  
  METHODS
  Quantitative analysis of evoked waveform data was performed on both sides in consecutive patients undergoing thyroid surgery by a single surgeon. Mean values, standard error of mean, and standard deviation were calculated for latency (in milliseconds) and amplitude (in microvolts) of the vagus nerves, RLN, and EBSLN. Pre- and postoperative vocal cord function was normal in all patients.
  
  
  RESULTS
  Normative latency analysis showed mean right and left vagal latency of 5.47 ms (±0.73) and 8.14 ms (±0.86), respectively (P < .0001). Pooled RLN latency was 3.96 ms (±0.69), and pooled EBSLN latency was 3.56 ms (±0.49), both significantly shorter than vagal latencies (P < .0001). There was no association between amplitude and latency parameters and tumor-size (> or <5 cm), body mass index (> or <25), age (> or <50 years), gender, or degree of neural dissection.
  
  
  CONCLUSIONS
  The unique right vagus, left vagus, and RLN latencies are characteristic of the individual nerves and allow identification (through the characteristic waveform latency) of an intact left or right vagus/RLN system. Timed recording of vagal waveform after thyroid lobectomy consequently documents intact ipsilateral vagal-RLN neural circuit and may be placed into the medical record as electrophysiologic documentation of existence of postresection complete neural integrity.
  
  
  METHODS
  4.
authors.affiliation: Division of Thyroid and Parathyroid Surgery, Department of Laryngology and Otology, Massachusetts Eye and Ear Infirmarym, Harvard Medical School, Boston, Massachusetts, U.S.A.
authors.forename: Niranjan
authors.initials: N
authors.lastname: Sritharan
authors.forename: Meghan
authors.initials: M
authors.lastname: Chase
authors.forename: Dipti
authors.initials: D
authors.lastname: Kamani
authors.forename: Madeline
authors.initials: M
authors.lastname: Randolph
authors.forename: Gregory W
authors.initials: GW
authors.lastname: Randolph
mesh_terms: D000328:Adult; D000368:Aged; D004576:Electromyography; D005260:Female; D006801:Humans; D007823:Laryngeal Nerves / Q000502:physiology*; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D011930:Reaction Time; D012009:Recurrent Laryngeal Nerve / Q000502:physiology*; D012815:Signal Processing, Computer-Assisted; D013959:Thyroid Diseases / Q000601:surgery; D014630:Vagus Nerve / Q000502:physiology*
keywords: Intraoperative nerve monitoring; bilateral vocal cord palsy; complications of thyroid surgery; electrophysiologic parameters; normal parameters; postoperative glottis and/or recurrent laryngeal nerve function; recurrent laryngeal nerve