Continuous vagal IONM prevents recurrent laryngeal nerve paralysis by revealing initial EMG changes of impending neuropraxic injury: a prospective, multicenter study

Abstract

Objectives/hypothesis: 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.

Study design: Prospective multicenter tertiary study.

Method: 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.

Level of evidence: 4.

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.