Clinical Validation of NerveTrend vs. Conventional i-IONM Mode of NIM Vital in Prevention of Recurrent Laryngeal Nerve Events During Bilateral Thyroid Surgery.

Over the past two decades, intraoperative neural monitoring (IONM) has evolved into a mature risk minimization tool. Meta-analyses of studies, most of which were limited by poor study designs and the sole use of intermittent nerve stimulation, failed to clearly demonstrate superiority of intermittent IONM (i-IONM) over anatomic visual recurrent laryngeal nerve (RLN) dissection in the absence of IONM. However, a substantial number of systematic reviews of i-IONM in thyroidectomy have conflicting results, but their mean methodological quality is critically low. Sanabria et al suggested that design of a systematic review should comply with methodological standards and recommendations to offer relevant and practical information for decision making. In particular, with the advent of continuous IONM (c-IONM), intraoperative nerve electromyographic tracings, registered almost in real time during the operation, accurately predict postoperative vocal fold function when International Neural Monitoring Study Group (INMSG) quality standards are adhered to. Despite promising data on benefits of c-IONM is still remains rarely utilized worldwide in thyroid surgery. C-IONM aids in avoiding permanent traction-related nerve injury by urging surgeons to reverse harmful surgical maneuvers. C-IONM also forms an integral part in the surgical concept of staged thyroidectomy. Delaying completion surgery on the other side until nerve function has recovered practically abolishes the risk of bilateral vocal fold palsy. C-IONM has greatly furthered our understanding of functional RLN injury, enabling conception of effective risk minimization strategies tailored to the individual patient. As recently reported by Schneider at al c-IONM is superior to i-IONM in preventing vocal cord palsy. Based on nerves at risk (5208 versus 5024 nerves), c-IONM had in this study a 1.7-fold lower early postoperative vocal cord palsy rate than i-IONM (1.5 versus 2.5 %). This translated into a 30-fold lower permanent vocal cord palsy rate (0.02 versus 0.6 %). Early postoperative vocal cord palsies were 17.9-fold less likely to become permanent with c-IONM than i-IONM.

On the other hand, a brand new NIM Vital equipment allows now for using i-IONM in quasi continuous mode which is termed NerveTrend mode. This concept is a natural evolution of i-IONM towards c-IONM mode but is operator dependent and not automatic as in c-IONM mode. Hence, careful clinical validation of NerveTrend mode is needed in order to identify its clinical pertinence with respect to preventing neural damage compared to the standard of i-IONM mode in thyroid surgery. A prospective, randomized study with 2 arms: i-IONM vs. NeveTrend mode (n=132 patients and 264 nerves at risk, each).

Patients who will sign the informed consent will be randomized to two groups: i-IONM vs. NerveTrend application during planned total thyroidectomy.

The standardized approach to IONM will be used as outlined by the guidelines of the International Neural Monitoring Study Group in Thyroid and Parathyroid Surgery.

All the operations will be performed under general anesthesia by two experienced endocrine surgeons (MB, AK) with annual volume of thyroid surgery > 300 cases, each. The anesthesia protocol is: intravenous midazolam premedication, induction with fentanyl, thiopental and suxamethonium, endotracheal intubation and sevoflurane maintenance. No other muscle relaxants are used during surgery. A standard cervicotomy is used in all the patients. Visual identification of RLN low in the neck (below the crossing with the inferior thyroid artery) will facilitated by the use of the IONM system employing the nerve mapping technique. Once the nerve iss visually identified, repeated stimulations with the IONM monopolar probe served to trace the nerve path in the operative field and test its functional integrity during dissection. In each patient, RLN will be exposed and the branches of the superior and inferior thyroid arteries will be divided close to the thyroid capsule.