Continuous intraoperative neural monitoring in thyroid surgery: a Mexican experience

Abstract

Intraoperative continuous neural monitoring (C-IONM) during thyroid surgery has been recognized as a useful tool to identify and confirm recurrent laryngeal nerve integrity. The aim of the present study is to analyze electromyographic features and thresholds for normal vocal fold function in our initial experience with C-IONM in thyroid surgery. C-IONM was utilized in 57 patients who underwent thyroid surgery between July 2012 and December 2015. EMG parameters were analyzed looking for potential predictors of postoperative vocal fold dismotility. There were 54 females (94.7%) and 3 males (5.3%) with a mean age of 46.7 ± 11.6 years. C-IONM was successfully registered in 89 of 107 nerves at risk (83.1%). Mean basal amplitude was 727.31 ± 471.25 μV and mean final amplitude was 650.27 ± 526.87 μV (P = 0.095, CI 95% 13.83-167.91). Mean basal latency was 5.23 ± 1.42 mS and mean final latency was 5.18 ± 1.50 mS (P = 0.594, CI 95% 0.39-0.24). Four patients had transient postoperative vocal fold paresis. None of these four patients had loss of signal (LOS), three had transient decrease in amplitude, and one had a normal registry throughout the operation. C-IONM is a useful tool to identify patients in whom intraoperative RLN is at risk during surgery. Final amplitude above 500 μV and no LOS is associated with RLN integrity and normal postoperative vocal fold function.

Future Directions of Neural Monitoring in Thyroid Surgery

“…Outcomes of IONM applied in evidence based medicine are no worse than those obtained by conventional thyroid surgery. Class I evidence is rarely obtained by IONM because IONM is rarely used to prevent RLN deficit and because the incidence of permanent RLN complications is low (8,11). Table 4 shows the future directions of IONM research that are needed to improve its outcomes.…”

“…Additionally, C-IONM provides comprehensive electromyography (EMG) documentation, detects imminent RLN failure, and reveals RLN stress mechanisms. Finally, C-IONM can reveal malposition of an EMG tube (7,8,12).…”

“…A major advantage of C-IONM is that, by alerting the surgeon to the potential for irreversible neural damage, it can reduce the risk of permanent RLN injury (7,8). For example, C-IONM can provide an early warning of impending neural injury by revealing adverse changes in EMG.…”

“…For example, C-IONM can provide an early warning of impending neural injury by revealing adverse changes in EMG. Nerve function can then be preserved by taking appropriate corrective action and by aborting maneuvers that can potentially cause adverse EMG changes and permanent vocal cord paralysis (VCP) (7,8). However, thyroid surgeons require effective methods for identifying important adverse events and for differentiating between true adverse events and artifacts (7,8,12).…”

“…Currently, both intermittent IONM (I-IONM) (2,3) and continuous IONM (C-IONM) (7,8) are recognized as effective techniques for RLN management. Studies also show that IONM can facilitate functional preservation of the external branch of the superior laryngeal nerve (SLN) (6).…”