Recurrent Laryngeal Nerve Stimulation Research Articles

Electrical Stimulation of Vocal Fold Adduction Triggered by Laryngeal Electromyography Using a Custom Implant.

Medialization procedures for unilateral vocal fold (VF) paralysis generally improve voice but do not fully replace dynamic VF adduction. Paralyzed VFs typically experience synkinetic reinnervation, which makes it feasible to elicit movement through electrical stimulation. We tested a novel laryngeal pacing implant capable of providing closed-loop (automatic) stimulation of a VF triggered by electromyography (EMG) potentials from the contralateral VF. A custom, battery-powered, microprocessor-based stimulator was tested in eight dogs with bipolar electrodes implanted for recording EMG from the left VF and stimulating adduction of the right VF. A cuff electrode on the left recurrent laryngeal nerve (RLN) stimulated unilateral VF adduction, modeling voluntary control in anesthetized animals. Closed-loop stimulation was tested in both acute and chronic experiments. Synkinetic reinnervation was created in two animals by right RLN transection and suture repair to model unilateral VF paralysis. In all animals, left VF activation through RLN stimulation generated a robust EMG response that rapidly triggered stimulation of contralateral thyroarytenoid and lateral cricoarytenoid muscles, causing nearly simultaneous bilateral adduction. Optimal triggering of VF stimulation from elicited EMG was achieved using independent onset and offset thresholds. Real-time artifact blanking allowed closed-loop stimulation without self-perpetuating feedback, despite the proximity of recording and stimulation electrodes. Using a custom implant system, we demonstrated real-time closed-loop stimulation of one VF triggered by the activation of the contralateral VF. This approach could potentially restore dynamic glottic closure for reflexive behaviors or phonation in cases of unilateral VF paralysis with synkinetic reinnervation. https://doi.org/10.23641/asha.24492133.

Recurrent laryngeal motor nerve conduction studies in a rat model: Establishing an objective measure for investigating laryngeal innervation.

Disease or injury can cause neuromuscular changes to the larynx that can affect voice, breathing, and swallowing. Motor nerve conduction studies have had limited use in the study of laryngeal neurophysiology, despite their importance in other anatomic sites. The aim of this study was to explore the feasibility of performing recurrent laryngeal motor nerve conduction studies (rlMNCS) in a rat model. rlMNCS were performed in 15 rats under anesthesia. A bipolar stimulating electrode was placed on the recurrent laryngeal nerve (RLN) 5 mm below the cricoid cartilage. Via direct laryngoscopy, a recording electrode was placed transorally into the thyroarytenoid muscle. The RLN was maximally stimulated to determine the compound muscle action potential (CMAP). Three consecutive trials were averaged. The mean stimulating threshold to the RLN to achieve a CMAP from the thyroarytenoid was 1.7 ± 0.6 mA. RLN stimulation caused a visible adductor twitch of the vocal fold in all animals. The mean negative amplitude was 2.0 ± 0.8 mV, and the total area was 1.0 ± 0.4 mV ms. The CMAP latency and negative duration were 1.0 ± 0.1 ms and 0.9 ± 0.2 ms, respectively. rlMNCS are feasible and may be useful in understanding laryngeal neurophysiology with disease or injury. This work could provide a tractable animal model for studying and monitoring treatment of neuromuscular conditions affecting voice, breathing, and swallowing.

The advantage of the combined use of intraoperative neuromonitoring and percutaneous ultrasonography of the larynx as a screening for postoperative vocal cord paresis

Background. One of the most common complications during thyroid surgery after hypoparathyroidism is a violation of the mobility of the vocal folds - paresis or paralysis of the larynx. The incidence of damage to the recurrent laryngeal nerves during primary surgical interventions can vary from 1 to 30%. Intraoperative neuromonitoring is the most effective method to reduce the amount of damage to the laryngeal nerves during surgical interventions on the thyroid and parathyroid glands. Assessment of the state of the vocal cords in the preoperative and postoperative period is crucial. In the preoperative period, this helps establish baseline characteristics and identify pre-existing laryngeal paresis, while postoperative early identification of vocal cord paresis helps develop a rapid treatment plan. Indirect laryngoscopy is still considered the reference standard for vocal cord examination. The main advantage is the ability to visualize the vocal cords in 99% of cases. However, this is an invasive procedure that can be painful and uncomfortable for patients, and increases medical costs and lead time.Materials and methods. The results of intraoperative neuromonitoring were analyzed in 25 patients who underwent total thyroidectomy according to indications (diffuse nodular non-toxic goiter — 17 patients (68%), diffuse nodular toxic goiter — 4 patients (16%), autoimmune thyroiditis, diffuse — nodular form — 4 patients (16%)), from September 2021 to February 2022. The patients’ age ranged from 18 to 73 years. There were 23 women (92%), men — 2 (8%). In the study, a C2 neuromonitor (InoMed, Germany), an electrode for EMG recording on an endotracheal tube, and a bipolar forked stimulating probe were used. To assess the mobility of the vocal folds, all patients underwent percutaneous ultrasonography before and after thyroid surgery.Results and discussion. In 20 patients (80%) before surgery on transcutaneous ultrasound of the larynx, the visualization of the structures of the larynx was good (grade 4-5), in 2 male patients (8%), the visualization of the structures of the larynx was satisfactory (grade 3), in 3 women (older than 45 years (12%)) — visualization of the structures of the larynx was satisfactory (grade 3), in all 25 patients (100%) — complete or normal symmetrical movement of the vocal folds (grade I). During the performance of precision extrafascial thyroidectomy in 3 patients (12%), a decrease in the amplitude of oscillations was recorded during stimulation of the left recurrent laryngeal nerve and the left vagus nerve, in order to prevent bilateral paresis of the larynx, it was decided to confine ourselves to hemithyroidectomy followed by a staged right-sided hemithyroidectomy. A day after the performed left-sided hemithyroidectomy, percutaneous ultrasound of the larynx in 2 patients showed a violation of the mobility of the vocal fold on the left (grade II), in 1 patient — symmetrical movement of the vocal folds (grade I) — a false positive reaction. In 22 patients (88%) who underwent total thyroidectomy on percutaneous ultrasound of the larynx, complete or normal symmetrical movement of the vocal folds (I degree).Conclusion. Intraoperative neuromonitoring is an effective tool to localize the recurrent laryngeal nerves regardless of whether a loss of signal (LOS) has occurred, as well as to determine the type of LOS (LOS 1, LOS 2) and staged thyroidectomy in the presence of LOS. Percutaneous vocal cord ultrasonography is currently an effective screening tool, saving 80% of patients from unnecessary invasive laryngoscopy. The complex of these methods should be an obligatory component in surgical interventions on the thyroid and parathyroid glands.

3D Reconstruction of Phonatory Glottal Shape and Volume: Effects of Neuromuscular Activation.

Although phonatory glottal posture and airflow pulse shape affect voice quality, studies to date have been limited by visualization of vocal fold (VF) vibration from a superior view. We performed a 3D reconstruction of VF vibratory motion during phonation from a medial view and assessed the glottal volume waveform and resulting acoustics as a function of neuromuscular stimulation. In vivo canine hemilarynx phonation. Across 121 unique combinations of the superior laryngeal nerve (SLN) and recurrent laryngeal nerve (RLN) stimulation, the hemilarynx was excited to the oscillation with airflow. VF medial surface reference points were tracked on high-speed video, mapped into 3D space, and surface shape was restored using cubic spline interpolation. Glottal surface shape, reconstruction-based parameters, and glottal volume waveform were calculated. Fundamental frequency (F0), cepstral peak prominence (CPP), and harmonic amplitude (H1-H2) were measured from high-quality audio samples. The glottis was convergent during opening and divergent during closing. Neuromuscular activation changed phonatory glottal shape and reduced glottal volume. Significant reduction in glottal volume and closing quotient were present with SLN stimulation. RLN stimulation significantly increased F0 and CPP and decreased H1-H2 (constricted glottis), while SLN effects were similar and synergistic with concurrent RLN stimulation. 3D reconstruction of in vivo medial surface vibration revealed effects of laryngeal nerve stimulation on glottal vibratory pattern and acoustic correlates of voice quality. SLN activation resulted in significantly quicker glottal closure per cycle, decreased glottal volume, and higher-pitched, less breathy, and less noisy voice. RLN had a similar effect on acoustic measures. NA, Basic Science Laryngoscope, 133:357-365, 2023.

Evaluation of the Cricothyroid Muscle Innervation Pattern Through Intraoperative Electromyography

Objectives:We observed significant contractions in the cricothyroid muscle (CTM) after recurrent laryngeal nerve (RLN) stimulation in some patients. We aimed to evaluate whether these contractions resulted from the laryngeal-muscle movement due to the contraction of other intrinsic muscles or actual CTM contraction, with objective real-time intraoperative electromyography (EMG) recordings.Methods:This study was performed prospectively in 106 consecutive patients who underwent intraoperative neural monitoring-guided primary thyroid surgery due to various thyroid diseases between February-2015 and February-2016. After completion of the thyroidectomy procedure; the RLN, vagus nerve (VN), external branch of the superior laryngeal nerve (EBSLN), plexus pharyngeus (PP), and contralateral EBSLN (CEBSLN) were stimulated and the responses from the CTM and CPM were recorded and evaluated by EMG through needle electrodes.Results:182 CTMs of 106 patients, with the mean age of 45, were evaluated regarding their innervation patterns. Positive EMG waveforms were achieved from 181 CTMs with EBSLN stimulation. A total of 132 (74%) positive EMG responses were recorded after the stimulation of 179 RLNs. The mean amplitude obtained with CTM EMG with RLN stimulation was 5.5% of that with EBSLN stimulation. The CTM amplitude was 39% of the vocal cord amplitude with RLN stimulation. Positive EMG responses of 96 CTMs (55%) with VN stimulation were recorded. The mean amplitude through CTM EMG with VN stimulation was 6% of that with EBSLN stimulation. Positive EMG responses were achieved from 10 (0.6%) CTMs with the stimulation of 170 PPs. The mean amplitude obtained from CTMs with PP stimulation was 4.3% of that with EBSLN stimulation. Positive EMG amplitudes of 35 (67%) CTMs were obtained with stimulation of 52 CEBSLN. Temporary vocal cord paralysis was detected in six patients (5% of patients and 3.3% of the nerves) postoperatively.Conclusion:The RLN contributes significantly to the innervation of the CTM. Despite the findings associated with the contribution of the PP and CEBSLN to the CTM innervation, further studies are needed. We are of the opinion that these are among the significant factors that contribute to the differences in clinical findings between patients with EBSLN injuries.

Investigation of potential neuropharmacological activity of neostigmine-glycopyrrolate for intraoperative neural monitoring in thyroid surgery.

Intraoperative neuromonitoring (IONM) is frequently used in thyroid surgery to reduce recurrent laryngeal nerve injury. The use of neuromuscular blockade agent to facilitate tracheal intubation, is a common cause of IONM failure. We performed a retrospective analysis to assess the efficacy of neostigmine-glycopyrrolate as a neuromuscular blockade reversal agent for IONM during thyroid surgery. Rocuronium (0.6mg/kg) was administered for muscle relaxation. Neostigmine (2mg) and glycopyrrolate (0.4mg) were administered immediately after intubation. Cricothyroid muscle-twitch response upon external branch of superior laryngeal nerve stimulation and electromyography amplitudes of vagal and recurrent laryngeal nerves before (V1, R1) and after thyroid resection (V2, R2) were recorded. Fifty patients (23 males, 27 females) were included in the analysis. The diagnoses comprised 43 papillary thyroid carcinomas and seven benign diseases. The mean time between rocuronium injection and neostigmine-glycopyrrolate injection was 5.1 ± 1.2min, and the mean time from neostigmine-glycopyrrolate injection to successful cricothyroid muscle twitching upon external branch of superior laryngeal nerve stimulation was 21.0 ± 4.5min. All patients had V1 and R1 amplitudes of more than 500 μV each, with mean V1 and R1 amplitudes of 985.3 ± 471.6μV and 1177.2 ± 572.7μV, respectively. Neostigmine-glycopyrrolate was effectively used as a neuromuscular blockade reversal agent for IONM in thyroid surgeries without a significant increase in bucking events. Administration of neostigmine-glycopyrrolate immediately after intubation can be recommended for successful NMB reversal to facilitate IONM during thyroid surgery.

Value of Neurostimulation Plus Laryngeal Palpation to Predict Postoperative Vocal Fold Motility

The aim of this study was to evaluate the reliability of intraoperative neuromonitoring through recurrent laryngeal nerve stimulation and simultaneous laryngeal palpation (NSLP) in predicting postoperative vocal cord palsy and in providing useful information in the decision to perform a staged surgery in initially planned total thyroidectomy. A retrospective review was performed involving 552 patients for whom a total thyroidectomy was planned. In all patients, preoperative and postoperative laryngoscopy was performed. The incidence of vocal cord palsy was calculated on 1104 nerves at risk. Sensitivity and specificity of NSLP were 0.9411 and 0.9925 respectively. The positive predictive value was 0.7804, the negative predictive value was 0.9981, the false positive rate was 0.8%. In 41 patients (7.4%) the initial surgical strategy was changed into a staged procedure. Nine patients (21.9%) were false positive, 32 patients (78.1%) were true positive. Finally, a two-stage thyroidectomy was performed in 27 of 41 patients. High sensitivity and specificity confirm the validity of NSLP in predicting postoperative vocal cord palsy and in driving a possible staged thyroidectomy, both in benign thyroid disease and in differentiated thyroid carcinoma.

Effects of Laryngeal Vibratory Asymmetry and Neuromuscular Compensation on Voice Quality.

Vibratory asymmetry and neuromuscular compensation are often seen in laryngeal neuromuscular pathology. However, the ramifications of these findings on voice quality are unclear. This study investigated the effects of varying levels of vibratory asymmetry and neuromuscular compensation on cepstral peak prominence (CPP), an analog of voice quality. In vivo canine phonation model. Varying degrees of vocal fold vibratory asymmetry were achieved by stimulating one recurrent laryngeal nerve (RLN) over 11 levels from threshold to maximal muscle activation. For each of these levels, phonation was induced at systematically varied combinations of neuromuscular compensation: three levels each of contralateral RLN stimulation (80%, 90%, and 100% of maximal), superior laryngeal nerve (SLN) activation (0%, 50%, and 100% of maximal), and airflow levels (500, 700, and 900 mL/s). Vocal fold symmetry was determined by assessing the opening phase of the vibratory cycle in high-speed video recordings. Voice quality was estimated acoustically by calculating CPP for each voice sample. Eight hundred twenty-two phonatory conditions with varying degrees of vibratory asymmetry were evaluated. CPP was highest at vibratory symmetry. Increasing levels of asymmetry resulted in significant decreases in CPP. CPP increased significantly with increasing contralateral RLN activation. CPP was significantly higher at 50% SLN activation than 0% or 100% SLN activation. Voice quality, as approximated by CPP, is best at vibratory symmetry and deteriorates with increasing degrees of asymmetry. Voice quality may be improved with neuromuscular compensation by increased adduction of the contralateral vocal fold or increased vocal fold tension at mid-levels of SLN activation. NA, Basic Science Laryngoscope, 132:130-134, 2022.

Perceptual Evaluation of Vocal Fold Vibratory Asymmetry

Laryngeal vibratory asymmetry occurring with paresis may result in a perceptually normal or abnormal voice. The present study aims to determine the relationships between the degree of vibratory asymmetry, acoustic measures, and perception of sound stimuli. Animal Model of Voice Production, Perceptual Analysis of Voice. In an in vivo canine model of phonation, symmetric and asymmetric laryngeal vibration were obtained via graded unilateral recurrent laryngeal nerve (RLN) stimulation simulating near paralysis to full activation. Phonation was performed at various contralateral RLN and bilateral superior laryngeal nerve stimulation levels. Naïve listeners rated the perceptual quality of 182 unique phonatory samples using a visual sort-and-rate task. Cepstral peak prominence (CPP) was calculated for each phonatory condition. The relationships among vibratory symmetry, CPP, and perceptual ratings were evaluated. A significant relationship emerged between RLN stimulation and perceptual rating, such that sound samples from low RLN levels were preferred to those from high RLN levels. When symmetric vibration was achieved at mid-RLN stimulation, listeners preferred samples from symmetric vibration over those from asymmetric vibration. However, when symmetry was achieved at high RLN levels, a strained voice quality resulted that listeners dispreferred over asymmetric conditions at lower RLN levels. CPP did not have a linear relationship with perceptual ratings. Laryngeal vibratory asymmetry produces variable perceptual differences in phonatory sound quality. Though CPP has been correlated with dysphonia in previous research, its complex relationship with quality limits its usefulness as clinical marker of voice quality perception. NA, basic science Laryngoscope, 131:2740-2746, 2021.

Low-Dose of Rocuronium During Thyroid Surgery: Effects on Intraoperative Nerve-Monitoring and Intubation

BackgroundIntraoperative Neurophysiological Monitoring (IONM) reduces the incidence of Recurrent Laryngeal Nerve (RLN) injuries during thyroid surgery. To preserve nerve function, long acting neuromuscular blocking agents (NMBA) should be avoided. However, NMBA are necessary for laryngoscopy and endotracheal intubation. We designed this double-blinded, randomized, placebo-controlled trial to assess if a low-dose of rocuronium given at intubation would affect the IONM data recorded before the thyroid dissection. MethodsHundred patients undergoing elective thyroid surgery were randomized to receive either 0.3 mg kg−1 of low dose rocuronium (intervention) or no-NMBA (control). Intubation was performed with video-laryngoscopy. IONM was placed on RLN and nerve stimulation was performed before and after thyroid dissection. The presence of a valid amplitude prior to dissection was defined when the IONM signal was >100 μV. Occurrence of difficult laryngoscopy was reported together with intubation details including time, difficulty and failure. The lowest peripheral saturation (SpO2) and the number of desaturation episodes during the intubation were also registered. ResultsNo patients showed impaired IONM signal before dissection in both groups. Cormack-Lehane grade was higher in the intervention group (11;2) compared to control one (11;1; P = 0.046). No-NMBA patients had increased number of difficult laryngoscopies (21% versus 6%, P = 0.041) and intubations (34% versus 8%; P = 0.003) as well as a longer time to intubation (78 [55; 175] versus 55 [31; 110] sec; P = 0.006). Lower values of peripheral SpO2 during intubation attempt were registered in the no NMBA group (99 [97; 100] versus 99 [99; 100] %; P = 0.020). However, the number of intubation failure was similar between groups (p=0.495). ConclusionsLow-dose of rocuronium does not compromise pre-dissection IONM signal and improves intubation condition when compared to a relaxant free strategy.

Time to Revisit a Low-Cost Alternative? Palpation Assessment Nerve Monitoring (PANM) for Recurrent Laryngeal Nerve to Predict Postoperative Vocal Cord Function-a Validation Study Using an In-House Neuromonitoring Device.

Neuromonitoring has proved to be a useful technique in reducing nerve injury during thyroid surgery; however, costs continue to limit its use in resource-constrained settings. This study was done to assess the functional integrity of the recurrent laryngeal nerve (RLN) during thyroid surgery using palpation assessment of posterior cricoarytenoid muscle twitch in response to RLN stimulation. Between August 2016 and July 2017, 24 patients with 47 nerves at risk (NARs) underwent thyroid surgery with visual identification and testing of 44 RLNs. The functional integrity of the RLN was checked by stimulation of the RLN. Intraoperative assessment showed 100% sensitivity and positive predictive value in predicting postoperative vocal cord function. The postoperative vocal cord assessment confirmed all 44 nerves tested to be normally functioning. The mean (standard deviation) peak-to-peak amplitude and latency of the CMAP were 0.889 (0.740)/1.336 (1.660) mV and 2.295 (0.319)/2.217 (0.393) ms for left/right side NARs, respectively, with no statistically significant difference (P > 0.05). Palpation assessment of the posterior cricoarytenoid muscle provides a simple and reliable technique for confirming integrity of the RLN. Combining palpation assessment with CMAP from the inferior constrictor muscle may help reduce potential false negative results. With the use of our in-house built device which is significantly cheaper than the commercial ones, this could be considered a low-cost alternative to current established techniques.

Development of In-Office Laryngeal Nerve Conduction Studies: Computed Tomography and Cadaveric Study.

In-office recurrent laryngeal nerve conduction studies (NCSs) are a technique that can potentially provide information about laryngeal innervation. NCS is essential in the management of other neuropathies including carpal tunnel syndrome and spinal cord injury. We hypothesize that laryngeal NCS may have similar utility in managing patients with vocal fold paralysis, atrophy, and neurodegenerative disease. NCSs are technically challenging because they require transcervical stimulation of the recurrent laryngeal nerve (RLN). This study combines radiographic data with cadaveric dissection to describe the anatomic parameters for optimal RLN stimulation. Radiographic and Cadaveric Study. Fifty computed tomography scans were reviewed to determine the dimensions for ideal needle electrode placement. These values were compared to measurements from 12 fresh human cadaveric neck dissections. Ultrasound imaging was utilized in select cases. The neck was dissected to assess the accuracy of electrode placement. Radiographically, the mean transcervical depth to the RLN was 33.2 mm ± 8.3 mm in males versus 29.4 mm ± 9.4 mm in females. The working space between the lateral trachea and carotid artery was 15.3 mm ± 3.6 mm on the right and 14.1 mm ± 2.9 mm on the left. After placement of stimulating electrodes into the cadaveric neck, the electrode tips were consistently within 8 mm of the RLN. Ultrasound guidance improved placement accuracy of the stimulating electrode. Laryngeal NCSs can provide detailed and objective information about laryngeal innervation that could dramatically improve the management of various neuropathies. In-office NCSs require technical precision, and this study describes anatomic factors that may affect the feasibility of performing this technique. NA Laryngoscope, 131:1566-1569, 2021.

Application of the original method of intra-operative electrophysiological stimulation of recurrent laryngeal nerve with surgical interventions on the neck organs

The OBJECTIVE was the reduction in the frequency of specific complications of surgical treatment of patients with pathology of the thyroid and parathyroid glands using the original method of monitoring the neuro-functional activity of the recurrent laryngeal nerve.METHODS AND MATERIALS. The research was conducted in two stages. At the first stage, the object of the topographic-anatomical study was 50 male and female corpses. The research, based on the fixed material, was focused upon the study of the anatomic special features of recurrent laryngeal nerves, their relations with neighboring structures, the study of peculiarities of recurrent laryngeal nerve syntopy and its neighboring structures to find the least traumatic way of incision during electroneurophysiological monitoring of activity. At the second stage, the object of the study was 60 patients with a benign pathology of the thyroid gland, who were operated on with the use of the original method of intra-operational visualization and control method over neuro-functional activity of recurrent laryngeal nerve.RESULTS. The frequency of the three different variants of topographic-anatomical position of recurrent laryngeal nerve depends on the side of the body. The safest, stable and the fastest one to be found is the left recurrent laryngeal nerve. Postoperative unilateral paresis of the larynx, diagnosed in 4 of 60 patients, is regarded as postischemic. Two-sided paresis of the larynx was diagnosed in 1 patient.CONCLUSION. This method allows to minimize the development of severe intraoperative complications, to reduce the frequency of postoperative paralysis and paresis of the larynx. Intra-operative visualization of recurrent laryngeal nerves is especially necessary during the repeated surgeries with postoperative scar transformations with wrong syntopy of neck organs and vascular-nerve structures, which makes it possible to minimize the number of postoperative paralyses and paresis of larynx and to get positive effect without carrying out the intubation of trachea among patients with postoperative paralysis of larynx or stenosis, and to avoid more serious damage of larynx or trachea in case of intubation.

Effects of Arytenoid Adduction Suture Position on Voice Production and Quality.

Arytenoid adduction (AA) is performed to treat unilateral vocal fold paralysis with a large posterior glottal gap. However, the voice effects of AA suture position remain unclear. This study aimed to evaluate voice production and quality as a function of AA suture position on the thyroid ala in a neuromuscularly intact in vivo larynx. Animal model. Unilateral recurrent laryngeal nerve and vagal paralysis were modeled in two canines. AA suture position was varied across five equidistant positions on the anterior inferior thyroid ala, from a paramedian position anteriorly to the oblique line posteriorly. Phonation was performed over 8 × 8 graded level combinations of recurrent and superior laryngeal nerve stimulation per suture position. The primary outcome was percent successful phonatory conditions. Secondary outcomes included fundamental frequency (F0), phonation onset pressure (PTP), cepstral peak prominence (CPP), and laryngeal posture. Anterior suture positions resulted in a greater percentage of successful phonatory conditions compared to posterior sutures. Suture position 2, located at the anterior inferior thyroid ala, resulted in the highest percentage of successful phonatory conditions, lowest PTP, and lower muscle activation levels to achieve higher CPP. Posterior sutures resulted in wider glottal gap and more effective F0 and vocal fold strain increase with cricothyroid muscle contraction, but with fewer successful phonatory conditions and higher PTP. Trends were consistent across both paralysis types. AA suture placed in the anterior inferior thyroid ala resulted in the best acoustic, aerodynamic, and voice quality outcomes. This study provides scientific evidence for maintaining current clinical practice. NA Laryngoscope, 131:846-852, 2021.

Recurrent laryngeal nerve management in transoral endoscopic thyroidectomy.

The mechanism of recurrent laryngeal nerve (RLN) injury was investigated during a TransOral Endoscopic Thyroidectomy Vestibular Approach (TOETVA). The function of 185 nerves at risk (NAR) was recorded with intermitted intraoperative neural monitoring (I-IONM). The RLN electromyography (EMG) was delineated during: (a) a pre-dissection vagal nerve stimulation; (b) a RLN stimulation at initial visualization; (c) at nerve dissection; and (d) at the final verification of the entire RLN route. The location, genesis, segmental or diffuse and the outcomes of RLN injuries were catalogued. Twelve nerves (6.4%) lost the EMG signal and the incidences of temporary and permanent RLN dysfunction were 5.9% and 0.5%. A disrupted point (type 1 injury) could be identified in 7/12 nerves (58%). Five (42%) nerve injuries were classified as global (type 2). Of the seven type 1 injuries, 3 lesions occurred at the RLN laryngeal entry point during the nerve identification. Four type 1 injuries were at the distal 1cm of the RLN course and during the early nerve dissection. No proximal (>2cm) injuries occurred. The mechanisms of the injuries were thermal (58%) during the energy-based device use at the ligament of Berry dissection or at the dividing small branches of the inferior thyroid artery. Two (16%) traction injuries occurred during the early nerve dissection. In 2 cases we could not elucidate the mechanism of RLN injury (16%) and 1 injury (8%) was caused by the connective tissue constricting band of. The thermal RLN lesions had longer recovery times. The RLN palsy occurs in TOETVA, even when combined with an endoscopic magnification, IONM, early nerve identification, cranial to caudal dissection and top-down view. The thermal RLN injury was the most frequent cause and all injuries occurred at the distal RLN course.

Effectiveness of intraoperative neuromonitoring of the recurrent laryngeal nerve with intermittent vagal nerve stimulation

Introduction: Vocal fold paralysis due to recurrent laryngeal nerve (RLN) injury during thyroidectomy occurs in 1-5% of patients, but it can reach up to 15% in reoperations. Intraoperative neuromonitoring (IONM) during thyroidectomy was first described in 1970, and has been widely used by surgeons. However, data on the IONM capacity to predict inferior laryngeal nerve function are still lacking. Objective: To evaluate the effectiveness of IONM of the RLN using intermittent stimulation of the vagus nerve during thyroidectomy to predict post-operative vocal fold function. Methods: Retrospective cohort analysis of 104 patients undergoing thyroidectomy with IONM of the RLN through intermittent vagal nerve stimulation. IONM response and vocal fold mobility were evaluated utilizing the McNemar’s test associated with the Kappa agreement coefficient. Results: The final response of RLN stimulation showed 69.23% sensitivity and 93.79% specificity (p=0.180). Conclusion: IONM of the RLN through intermittent vagal nerve stimulation during thyroidectomy is effective to predict post-operative vocal fold function.

Recurrent laryngeal nerve monitoring with surface electrodes in pediatric thyroid surgery.

To prospectively evaluate 1) use of endotracheal tube (ETT) surface electrodes for recurrent laryngeal nerve (RLN) monitoring in thyroid surgery in children, and 2) effects of thyroid surgery on the RLN in children. Patients <18 years old undergoing thyroidectomy were included. Vocal cord mobility was assessed pre- and postoperatively. RLNs were monitored using adhesive or integrated electrodes. Recordings were made before and after dissection, and area under the curve and latency were compared using mixed models. Twenty-five children (44 nerves at risk), mean (standard deviation) age 13.1 (3.4) years (range 4.5-17.4 years), underwent thyroidectomy. Twelve (46%) monitors were adhesive. One nerve had unobtainable responses. Nerveäna Power Index (NPI) (Neurovision Medical Products, Ventura, CA) decreased, and latency increased pre- versus postdissection at all amplitudes (P < 0.0001), with change in slope of NPI affected by tumor size (P < 0.05). Postdissection, the NPI was lower, and the latency was longer when stimulating low in the neck versus near the cricothyroid joint at all stimulating amplitudes (P < 0.0001), with change in NPI related to tumor size (P < 0.0001). Changes were not associated with decreased vocal cord mobility, aspiration, or voice change. One patient had a temporary unilateral paresis that resolved by 7 weeks, and another had normal movement 3 weeks postoperatively and developed a paresis 2 months postoperatively. ETT surface electrodes are reliable for RLN monitoring in thyroid surgery in children. Thyroid surgery is associated with a decrease in RLN stimulability that is related to tumor size. The site of RLN stimulation matters when evaluating the nerve. 4 Laryngoscope, 130:1583-1589, 2020.

Selective stimulation of human intrinsic laryngeal muscles: Analysis in a mathematical three‐dimensional space

Standard stimulating methods using square waves do not appropriately restore physiological control of individual intrinsic laryngeal muscles (ILMs). To further explore our earlier study of evoked orderly recruitment by quasitrapezoidal (QT) currents, we integrated the contribution of the cricothyroideus (CT) with attention to mutual activation in an additional patient, based on recent studies of appropriate responses via strict recurrent laryngeal nerve (RLN) stimulation. Basic science study. The patient received functional electrical stimulation (FES) with QT pulses at 5 Hz, 60 to 2,000 μAmp, 100 to 500 μs pulse width, 0 to 500 μs decay. Ipsilateral electromyography (EMG) responses were calculated using the average maximum amplitude, area under the curve, and the root mean square of the rectified amplitude waveforms. The thyroarytenoideus (TA), posterior cricoarytenoideus (PCA), lateral cricothyroideus (LCA), and the CT were each interrogated via two monopolar electrodes, values were recorded in MATLAB, exported to Excel, and analyzed. Individual and mutual recruitment configurations and activation delays with stimulation were explored using multiple regression and exploration factor analyses. A total of 868 EMG data points based on 18 trials and up to 11 subtrials were captured from each of the four ILMs. Various combinations of pulse amplitude, pulse width, and exponential decay were found to produce significant (P ≤ .001) individual ILM responses. CT mirrored the LCA, whereas the TA and PCA exhibited separate interactions along shared trajectories in a three-dimensional space. FES calibrated to individual and coupled ILMs offers promise for restoring normal and pathological contraction patterns via strict RLN stimulation. 5 Laryngoscope, 130:967-973, 2020.

Development of radiofrequency ablation devices with neuromonitoring system to detect recurrent laryngeal nerve in thyroid nodule

Background Radiofrequency ablation (RFA) is an emerging minimally invasive treatment modality of benign thyroid nodule and limited small papillary thyroid cancer. Among the RFA related complications, the recurrent laryngeal nerve (RLN) damage is one of the most concerned complications. To reduce the RLN injury during RFA, we developed a RFA device with intraoperative neuromonitoring system (IONM) to detect recurrent laryngeal nerve. Furthermore, to avoid a use of EMG tube requiring general anesthesia, we developed an accelerometer sensor that can be attached on the anterior neck skin. In this study, we examined the feasibility of neuromonitoring system to detect RLN during RFA in thyroid gland. Methods Three beagles (six thyroid glands) underwent the RFA under general anesthesia. Tip of the RF electrode acted as a neurostimulator probe and its location was ultrasonographically monitored. Stimulation current was set based on NIM-Response 3.0 system. During the procedure, nervemonitoring was performed simultaneously using NIM® standard EMG reinforced tube, needle electrode and accelerometer. Results When the tip of the RF electrode was placed near the tracheoesophageal groove, RLN was successfully identified with EMG tube, needle electrode and accelerometer sensor. After RFA near the tracheoesophageal groove, nerve injury was detected in EMG tube, needle electrode and accelerometer sensor. Conclusion Neuromonitoring system to detect RLN using RF electrode was feasible in the animal study. Like both EMG tube and needle electrode, the accelerometer sensor can detect laryngeal muscle twitching during RLN stimulation. Accelerometer sensor for detecting RLN is expected to make the RFA procedure safer without any invasive monitoring system.

Anterior laryngeal electrodes for recurrent laryngeal nerve monitoring during thyroid and parathyroid surgery: New expanded options for neural monitoring.

Intraoperative neural monitoring is a useful adjunct for the laryngeal nerve function assessment during thyroid and parathyroid surgery. Typically, monitoring is performed by measurement of electromyographic responses recorded by endotracheal tube (ETT) surface electrodes. Tube position alterations during surgery can cause displacement of the electrodes relative to the vocal cords, leading to false positive loss of signal. Numerous reports have denoted monitoring equipment-related issues, especially endotracheal tube displacement, as the dominant source of false positive error. The false positive error may result in inappropriate decisions by the surgeon. This study tests the hypothesis that anterior laryngeal electrodes (ALEs) can help reduce this error. Placement of ALEs directly onto the thyroid cartilage represent an adjunctive and possible alternative method to standard ETT surface electrodes. Retrospective review. Fifteen consecutive patients undergoing thyroid and parathyroid surgery with intraoperative neuromonitoring using both ETT electrodes and ALEs were studied. Data collected included site of neural stimulation, laterality, and electromyographic parameters. With vagal and recurrent laryngeal nerve stimulation, the ALEs recorded mean vocalis muscle waveform amplitude within 83% of that recorded with standard ETT electrodes. The latency measurements with the anterior laryngeal and endotracheal electrodes were similar, with both electrodes recording significantly longer latency for the left vagus nerve as compared to the right vagus nerve. With superior laryngeal nerve stimulation, the ALEs recorded a 800% greater mean amplitude than the ETT electrodes. The ALEs demonstrated similar sensitivity to stimulation at low current as ETT electrodes and provided stable intraoperative monitoring information. Compared to ETT surface electrodes, the ALEs provide similar and stable electromyographic responses with equal sensitivity for recording evoked responses during neural monitoring in thyroid and parathyroid surgery. The ALEs offer significantly more robust monitoring of the external branch of the superior laryngeal nerve. Furthermore, ALEs are contained within the operative field, are totally surgeon controlled, and are unaffected by the potential vicissitudes of ETT position during surgery. 4 Laryngoscope, 128:2910-2915, 2018.