The long-term impact of routine intraoperative nerve monitoring during thyroid and parathyroid surgery

Background Despite widespread use of intraoperative nerve monitoring (IONM) as an adjunct to visual identification of the recurrent laryngeal nerve (RLN), published studies have shown little or no benefit. No long-term studies exist detailing the effect of experience gained from IONM on the rate of RLN injury. The aim of this study was to evaluate the impact of IONM feedback on surgical outcomes over time at a single institution. Methods We conducted retrospective analysis of prospectively gathered data for 1,936 patients including 3,435 nerves at risk between March 2004 and September 2011. Each RLN was analyzed for the specific, unilateral operative procedure that placed the nerve at risk of injury. The primary outcome measures included temporary vocal cord palsy and permanent vocal cord paralysis or paresis as determined by intraoperative loss of RLN function and postoperative laryngoscopy. Additional measures included instances where IONM assisted the surgeon's localization of the RLN. Results Of the 3,435 nerves at risk, 105 (3.06%) were injured, 4 had permanent paralysis (0.12%), and 7 had paresis (0.20%). Over time, a decrease in RLN injury was seen per successive operative year for thyroid lobectomy with paratracheal lymph node dissection with or without parathyroidectomy (odds ratio, 0.98; 95% confidence interval, 0.97-1.00; P =.04); the rate of nerve injury stabilized after 20 months of continued use of nerve monitoring. IONM particularly assisted the surgeon with identification of 108 nerves at risk (3.14%) with aberrant anatomy, and with identification of 236 nerves at risk (6.87%) during difficult dissections. Conclusion With experience, routine use of IONM during thyroid and parathyroid operations significantly decreased the incidence of injury to the RLN for thyroid lobectomy with paratracheal lymph node dissection and provided useful assistance with RLN identification for 10% of nerves at risk.