title: Continuous vagal IONM prevents recurrent laryngeal nerve paralysis by revealing initial EMG changes of impending neuropraxic injury: a prospective, multicenter study.
abstract: OBJECTIVE
  Existing intraoperative neuromonitoring (IONM) formats stimulate the recurrent laryngeal nerve (RLN) intermittently, exposing it to risk for injury in between stimulations. We report electrophysiologic parameters of continuous vagal monitoring, utilizing a novel real-time IONM format, and relate these parameters to intraoperative surgical maneuvers that delineate nascent adverse but reversible electrophysiologic parameters to prevent nerve injury. These results are correlated with postoperative vocal cord functional outcome.
  
  
  METHODS
  Prospective multicenter tertiary study.
  
  
  METHODS
  Evoked vagal nerve waveform amplitude and latency changes during 102 thyroidectomies were recorded. Adverse electrophysiologic response was categorized into 1-concordant amplitude reduction and latency increase events (combined events) and 2-loss of signal (LOS). Surgical maneuvers were modified when adverse electrophysiologic findings were noted. All patients underwent preoperative and postoperative laryngoscopy; intraoperative electrophysiologic findings were correlated with postoperative laryngeal function.
  
  
  RESULTS
  Continuous vagal monitoring did not result in stimulation-evoked nerve injury or intraoperative adverse cardiac, pulmonary, or gastrointestinal effects. Both intraoperative combined events and LOS were associated with development of vocal cord paralysis (VCP) (P = 0.001 and P >0.001 respectively). Combined events had a positive predictive value (PPV) of 33%, negative predictive value (NPV) of 97%, and were reversible in 73%. LOS had a PPV of 83%, NPV of 98%, and was reversible in only 17%. Milder combined events and isolated amplitude or latency changes were not associated with VCP.
  
  
  CONCLUSIONS
  Continuous vagal monitoring is safe and provides real-time RLN evaluation during surgical maneuvers. Combined events and LOS, both easily identifiable intraoperatively, are related to the development of VCP. A combined event represents a largely reversible electrophysiologic change when the associated surgical maneuver is aborted. If allowed to continue, it can advance to LOS (which typically is significantly less reversible) and to postoperative VCP. Continuous vagal monitoring has utility in identifying real-time adverse concordant amplitude and latency changes (combined events), which can prompt modification of the associated surgical maneuver and may prevent RLN paralysis during thyroidectomy.
  
  
  METHODS
  4.
authors.affiliation: Division of Thyroid and Parathyroid Surgery, Department of Laryngology and Otology, Massachusetts Eye and Ear Infirmary, Harvard Medical School, Boston, Massachusetts.
authors.forename: Eimear
authors.initials: E
authors.lastname: Phelan
authors.forename: Rick
authors.initials: R
authors.lastname: Schneider
authors.forename: Kerstin
authors.initials: K
authors.lastname: Lorenz
authors.forename: Henning
authors.initials: H
authors.lastname: Dralle
authors.forename: Dipti
authors.initials: D
authors.lastname: Kamani
authors.forename: Andre
authors.initials: A
authors.lastname: Potenza
authors.forename: Niranjan
authors.initials: N
authors.lastname: Sritharan
authors.forename: Jenifer
authors.initials: J
authors.lastname: Shin
authors.forename: Gregory
authors.initials: G
authors.lastname: W Randolph
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D004576:Electromyography / Q000379:methods; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D008875:Middle Aged; D016343:Monitoring, Intraoperative / Q000379:methods*; D011237:Predictive Value of Tests; D011446:Prospective Studies; D012372:ROC Curve; D061226:Recurrent Laryngeal Nerve Injuries / Q000517:prevention & control*; D018570:Risk Assessment; D013959:Thyroid Diseases / Q000473:pathology / Q000601:surgery*; D013965:Thyroidectomy / Q000009:adverse effects* / Q000379:methods; D016896:Treatment Outcome; D055536:Vagus Nerve Stimulation / Q000379:methods*; D014826:Vocal Cord Paralysis / Q000517:prevention & control; D055815:Young Adult
keywords: CIONM; Continuous vagal monitoring; IONM; adverse EMG changes; amplitude and latency changes; combined events; neuromonitoring; recurrent laryngeal nerve injury; recurrent laryngeal nerve paralysis; thyroid surgery; vagal electrodes; vocal cord paralysis