Continuous Intraoperative Recurrent Laryngeal Nerve Monitoring: Techniques, Applications, and Controversies

Abstract

Purpose of Review Purpose of the present review is to illustrate the current state of the art concerning continuous intraoperative recurrent laryngeal nerve monitoring (cIONM) for thyroid surgery. Recent Findings cIONM potentially leads to an improved postoperative vocal cord palsy rate, compared to the intermittent technique. There are currently two main approaches for cIONM: either conventional cIONM based on vagal nerve stimulation or experimental methods, which do not require the positioning of a vagal nerve electrode. One of these methods is the recently described technique “LAR-cIONM,” which utilizes the laryngeal adductor reflex. Summary cIONM represents an advancement of intermittent nerve monitoring, which allows for an immediate reaction to signal changes. Threshold values and guidelines to prevent recurrent laryngeal nerve palsy were validated for the direct stimulation of the vagal nerve and require verification for alterative cIONM methods, including LAR-cIONM.

Intraoperative recurrent laryngeal nerve monitoring versus visualisation alone - A systematic review and meta-analysis of randomized controlled trials

“…3 This method of neuromonitoring can be performed intermittently through ipsilateral stimulation of the RLN using a handheld monopolar or bipolar probe, 4 or continuously by ipsilateral vagal nerve stimulation via clip electrodes mounted upon the vagus nerve. 5,6 At present, data from Europe and the United States suggests that 93%-98% of head and neck and endocrine surgeons routinely use either form of IONM to confirm location of the RLN during surgery. 7,8 While there is a recent trend favouring robust IONM utilisation to identify and establish the integrity of the RLNs, uptake of continuous IONM has been modest, with intermittent IONM still being used in greater than 80.0% of European facilities.…”

Continuous Intraoperative Nerve Monitoring of a Non-Recurrent Laryngeal Nerve: Real-Life Data of a High-Volume Thyroid Surgery Center

“…Also, cIONM might be able to prevent injury to all variants of the laryngeal nerve due to the real-time evaluation of the vagus nerve/RLN axis. Nevertheless, cIONM usage needs experience, and all surgeons must be aware of cIONM-related technical pitfalls, such as incorrect positioning of the endotracheal electrode or the occurrence of a laryngeal twitch [ 13 , 19 , 21 ]. In our evaluation, two patients showed a permanent drop of the cIONM signal amplitude during surgery without a clinically apparent VCP after surgery.…”

“…For IONM, suprathreshold stimulation (1–2 mA) of the vagus nerve and RLN is performed with a hand-held stimulation probe. Surface electrodes on the endotracheal tube, which are positioned at the level of the vocal folds, subsequently register the compound muscle action potentials of the laryngeal muscles [ 13 ]. A novel technique to enable real-time evaluation of the nerve’s functionality is continuous intraoperative nerve monitoring (cIONM) [ 13 ].…”

“…Surface electrodes on the endotracheal tube, which are positioned at the level of the vocal folds, subsequently register the compound muscle action potentials of the laryngeal muscles [ 13 ]. A novel technique to enable real-time evaluation of the nerve’s functionality is continuous intraoperative nerve monitoring (cIONM) [ 13 ]. Also, cIONM complements the technique of IONM with repetitive stimulation, which offers the advantage of an immediate feedback in case of imminent traction damage to the RLN [ 14 , 15 ].…”

Impact of direct laryngoscopy vs. videolaryngoscopy on signal quality of recurrent laryngeal nerve monitoring in thyroid surgery: a randomised parallel group trial

“…In some patients, the relative position between the exposed surface electrodes and vocal cords may not be clearly identified because of the poor view under direct laryngoscopy [3][4][5]. Videolaryngoscopy is associated with a better glottic view [12][13][14][15][16][17][18]. Currently, there is a lack of evidence as to whether videolaryngoscopy facilitates improved intra-operative neuromonitoring through an optimised glottic view in patients undergoing elective thyroid surgery with normal airways.…”