A new vagal anchor electrode for real-time monitoring of the recurrent laryngeal nerve

A Prospective Study of Electromyographic Amplitude Changes During Intraoperative Neural Monitoring for Open Thyroidectomy

BACKGROUND

Intraoperative nerve monitoring (IONM) of the vagus and recurrent laryngeal nerve (RLN) enables prediction of postoperative nerve function. The underlying mechanism for loss of signal (LOS) in a visually intact nerve is poorly understood. The correlation of intraoperative electromyographic amplitude changes (EMG) with surgical manoeuvres could help identify mechanisms of LOS during conventional thyroidectomy.

METHODS

A prospective study of consecutive patients undergoing thyroidectomy was performed with intermittent IONM using the NIM Vital nerve monitoring system. The ipsilateral vagus and RLN was stimulated, and vagus nerve signal amplitude recorded at five time points during thyroidectomy (baseline, after mobilisation of superior pole, medialisation of the thyroid lobe, before release at Ligament of Berry, end of case). RLN signal amplitude was recorded at two time points; after medialisation of the thyroid lobe (R1), and end of case (R2).

RESULTS

A total of 100 consecutive patients undergoing thyroidectomy were studied with 126 RLN at risk. The overall rate of LOS was 4.0%. Cases without LOS demonstrated a highly significant vagus nerve median percentage amplitude drop at medialisation of the thyroid lobe (- 17.9 ± 53.1%, P < 0.001), and end of case (- 16.0 ± 47.2%, P < 0.001) compared to baseline. RLN had no significant amplitude drop at R2 compared to R1 (P = 0.207).

CONCLUSIONS

A significant reduction in vagus nerve EMG amplitude at medialisation of the thyroid and the end of case compared to baseline indicates that stretch injury or traction forces during thyroid mobilisation are the most likely mechanism of RLN impairment during conventional thyroidectomy.

Continuous intraoperative neuromonitoring of the recurrent laryngeal nerve by eliciting the laryngeal adductor reflex (LAR-CIONM)

The laryngeal adductor reflex (LAR) is a life-sustaining airway protective mechanism that serves to shield the lower airways from inhaled foreign bodies. Over the past half century, the LAR has been extensively investigated and its dysfunction has been linked to far-ranging pathologies, from dysphagia to sudden infant death syndrome. Over the past 6 years, specific electromyographic waves in the LAR response have been used to devise a methodology for monitoring the vagus and recurrently laryngeal nerves during surgical procedures. This methodology involves continuous intraoperative neuromonitoring of the laryngeal adductor reflex and isthus termed 'LAR-CIONM'. In this review paper, the physiology of the LAR will be summarized as it relates to LAR-CIONM and the technique of LAR-CIONM will be described. Applications of this technique and published outcomes of LAR-CIONM will be highlighted.

Continuous vagal intraoperative neuromonitoring during video-assisted thoracoscopic surgery for left lung cancer: its efficacy in preventing permanent vocal cord paralysis

OBJECTIVES

We investigated the safety and efficacy of continuous intraoperative neuromonitoring (CIONM) during video-assisted thoracoscopic lobectomy for left lung cancer in preventing recurrent laryngeal nerve injury.

METHODS

From August 2015 to March 2020, 22 patients with left lung cancer without CIONM (unmonitored) and 20 patients with left lung cancer with CIONM underwent thoracoscopic lobectomy with complete mediastinal lymph node dissection including 4L dissection. Clinical outcomes from these 2 groups were compared.

RESULTS

The incidence of 4L metastasis was 7.14% (3 patients). There was no significant difference in the total number of dissected 4L lymph nodes between the 2 groups (3.23 ± 2.2 in the unmonitored group, 3.95 ± 2.0 in the CIONM group). CIONM was successful in all of the cases. There was no significant difference in the incidence of postoperative vocal cord palsy (22.7% in the unmonitored group, 20% in the CIONM group, P = 1.000). All of the 5 patients (100%) had permanent vocal cord palsy in the unmonitored group. Although statistically insignificant, 75% (3 patients) had total recovery of the vocal cord function, with only 1 patient remaining in permanent vocal cord palsy in the CIONM group.

CONCLUSIONS

CIONM was safe and efficient. CIONM might be helpful to avoid permanent vocal cord palsy by immediately warning the surgeon about impending nerve injury, so the surgeon can stop delivering further injury to the recurrent laryngeal nerve.

Clarifying optimal outcome measures in intermittent and continuous laryngeal neuromonitoring

BACKGROUND

Intraoperative neuromonitoring (IONM) techniques have evolved over the past decade into intermittent IONM (I-IONM) and continuous IONM (C-IONM) modes of application. Despite many prior publications on both types of IONM, there remains uncertainty about what outcomes should be measured for each form of IONM. The primary objective of this paper is to define categories of benefit for I-IONM/C-IONM and to clarify and standardize their reporting outcomes.

METHODS

Expert review consensus statement utilizing modified Delphi methodology.

RESULTS

I-IONM provides diagnosis, classification, and prevention of nerve injury through accurate and early nerve identification. C-IONM provides real-time information on nerve functional integrity and thus may prevent some types of nerve injury but cannot assist in nerve localization. Sudden mechanisms of nerve injury cannot be predicted or prevented by either technique.

CONCLUSIONS

I-IONM and C-IONM are complementary techniques. Future studies evaluating the utility of IONM should focus on outcomes that are appropriate to the type of IONM being utilized.

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

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.

Critical Review and Consensus Statement for Neural Monitoring in Otolaryngologic Head, Neck, and Endocrine Surgery

BACKGROUND

Enhancing patient outcomes in an array of surgical procedures in the head and neck requires the maintenance of complex regional functions through the protection of cranial nerve integrity. This review and consensus statement cover the scope of cranial nerve monitoring of all cranial nerves that are of practical importance in head, neck, and endocrine surgery except for cranial nerves VII and VIII within the temporal bone. Complete and applied understanding of neurophysiologic principles facilitates the surgeon's ability to monitor the at-risk nerve.

METHODS

The American Academy of Otolaryngology-Head and Neck Surgery (AAO-HNS) identified the need for a consensus statement on cranial nerve monitoring. An AAO-HNS task force was created through soliciting experts on the subject. Relevant domains were identified, including residency education, neurophysiology, application, and various techniques for monitoring pertinent cranial nerves. A document was generated to incorporate and consolidate these domains. The panel used a modified Delphi method for consensus generation.

RESULTS

Consensus was achieved in the domains of education needs and anesthesia considerations, as well as setup, troubleshooting, and documentation. Specific cranial nerve monitoring was evaluated and reached consensus for all cranial nerves in statement 4 with the exception of the spinal accessory nerve. Although the spinal accessory nerve's value can never be marginalized, the task force did not feel that the existing literature was as robust to support a recommendation of routine monitoring of this nerve. In contrast, there is robust supporting literature cited and consensus for routine monitoring in certain procedures, such as thyroid surgery, to optimize patient outcomes.

CONCLUSIONS

The AAO-HNS Cranial Nerve Monitoring Task Force has provided a state-of-the-art review in neural monitoring in otolaryngologic head, neck, and endocrine surgery. The evidence-based review was complemented by consensus statements utilizing a modified Delphi method to prioritize key statements to enhance patient outcomes in an array of surgical procedures in the head and neck. A precise definition of what actually constitutes intraoperative nerve monitoring and its benefits have been provided.

Non-energy devices to dissect recurrent laryngeal nerve lymph nodes of non-small cell lung cancer under video-assisted thoracic surgery

Background

Systematic nodal dissection plays a crucial role in improving survival and staging in resectable non-small cell lung cancer (NSCLC) patients but at the cost of increasing the occurrence of recurrent laryngeal nerve injury. Technology should be improved to protect the recurrent laryngeal nerve (RLN) during surgery.

Methods

NSCLC patients who underwent video-assisted thoracic surgery (VATS) surgical treatment by the same surgeon at our hospital from January 2016 to December 2017 were included as the research subjects and were divided into an energy-device group and a non-energy-device group. Their procedures included anatomic pulmonary resection, normative N1 dissection, and systemic N2 dissection.

Results

The rate of metastatically involved recurrent laryngeal nerve lymph nodes (RLNLNs) was 5.19% (39/752). Dissection device, side of primary, FEV1, operative time and BMI were independent predictors of recurrent laryngeal nerve injury (RLNI) (hazard ratio (HR) = 3.576, 95% confidence interval (CI): 1.490–8.583, P = 0.004; HR = 0.175, 95% CI: 0.072–0.424, P =  < 0.001; HR = 3.008, 95% CI: 1.30–6.927, P = 0.010; HR = 0.328, 95% CI: 0.136–0.794, P = 0.013; HR = 0.344, 95%CI: 0.147–0.801, P = 0.013, respectively). Patients in the non-energy-device group had significantly less RLNI than the energy-device group (P = 0.016) and nearly half of the non-thermal RLNI recovered in 2 weeks (P = 0.025) whereas most thermal RLNI required 3 months for recovery.

Conclusions

Every station of RLNLN had some degree of cancer metastasis in NSCLC patients and when dissecting RLNLNs, dissection device was an independent and artificially controlled predictor of RLNI. Using a non-energy device is a feasible method to protect the RLN as well as an improved recovery time of RLNI.

An experimental study on intraoperative recovery of recurrent laryngeal nerve function

OBJECTIVE

If bilateral thyroid surgery is planned and staged thyroidectomy considered in case of loss of neuromonitoring signal (LOS), a waiting time of 20 minutes is suggested for evaluation of early nerve recovery. This recommendation is based on clinical observations and has not been thoroughly validated experimentally.

METHODS

Sixteen pigs were randomly studied, and electromyogram (EMG) was continuously recorded during traction injury until an amplitude decrease of 70% from baseline (BL) (16 nerves) or LOS (16 nerves), and further during 40-minute recovery time. At the end of the experiments, vocal cord twitch was evaluated by video-laryngoscopy.

RESULTS

In the 70% group, 8 of 16 nerves recovered to or above an amplitude of 50% of baseline after 20 minutes and finally one more after 40 minutes. In the LOS group, only one nerve showed recovery after 20 minutes and one more after 40 minutes. Video-laryngoscopy revealed good or strong vocal cord twitches, in 10 of 14 nerves in the 70% group and in only 2 of 14 nerves in the LOS group.

CONCLUSIONS

The overall intraoperative recovery was low after LOS. Even after 70% amplitude depression, only half of the nerves showed recovery to amplitudes ≥50% of BL. Nerve recovery is dynamic, and a waiting time of 20 minutes seems appropriate for the identification of early nerve recovery before decisions are taken to continue or terminate surgery. The final EMG amplitude was not always well correlated with estimated vocal cord twitch, evaluated by video-laryngoscopy. This observation needs further investigation.

Continuous Laryngeal Adductor Reflex Versus Intermittent Nerve Monitoring in Neck Endocrine Surgery

OBJECTIVE

Intraoperative neuromonitoring (IONM) techniques aim to identify and potentially prevent nerve injury during surgeries. Prior studies into the efficacy of recurrent laryngeal nerve (RLN) IONM convey mixed results, with some claiming equivalence between IONM and no monitoring at all. The goal of the current study was to compare continuous RLN monitoring using the laryngeal adductor reflex (LAR) to intermittent RLN monitoring (intermittent IONM) to determine whether continuous monitoring reduces the incidence of intraoperative RLN injury during neck endocrine surgeries.

METHODS

In this observational, historical case-control study, a historical cohort of patients monitored with intermittent-IONM (group 1, n = 130) were compared to prospectively collected data from consecutive nerves-at-risk monitored continuously with the LAR (LAR-CIONM, group 2, n = 205), at a single center by a single surgeon. The test benefit ratio and relative risk reduction (RRR) for LAR-CIONM over intermittent IONM were calculated.

RESULTS

For group 1, nine nerves at risk exhibited intraoperative LOS with transient postoperative vocal fold (VF) hypomobility (n = 2) or immobility (VFI, n = 7). For group 2, two nerves at risk (0.98%) had sudden intraoperative LAR LOS following bipolar cautery, resulting in postoperative transient VFI (P = .004). In each group, there was one case of permanent postoperative VFI. The test benefit rate ratio for LAR-CIONM demonstrated a dramatic effect at 5.23, with an RRR of 81.0%.

CONCLUSION

LAR-CIONM significantly decreased rates of postoperative transient VF paralysis and paresis over intermittent IONM alone (P = .004). Surgeons should be aware of the benefits and limitations of intermittent IONM versus CIONM. Intermittent IONM, although useful in nerve mapping and intraoperative decision making, has minimal benefit for the prevention of nerve injury, whereas CIONM can potentially reduce nerve injury rates and improve patient outcomes.

LEVEL OF EVIDENCE

3 Laryngoscope, 131:230-236, 2021.

Continuous Neural Monitoring in Endoscopic Thyroidectomy: Feasibility Experimental Study for Transcutaneous Vagal Nerve Stimulation

Background: Adoption of continuous intraoperative neural monitoring (C-IONM) in endoscopic thyroid surgery is limited due to the uneasy application of C-IONM electrode. Feasibility for transcutaneous vagal nerve stimulation was tested. Materials and Methods: Vagus nerve (VN) and recurrent laryngeal nerve (RLN) were mapped and stimulated in different neck sites by (1) transcutaneous monopolar intermitted stimulation; (2) prototype for continuous transcutaneous stimulating electrodes (TSEs), that is, suction ball C-IONM electrode remodeled; (3) stimulation subsequently to neck CO₂ insufflation; (4) direct stimulation of surgical exposed nerves. Electromyographic (EMG) parameters were compared. Results: Six anterior neck locations evoked EMG signals of VNs and RLNs. Location Nos. 3 and 6 according to our scheme were over the VNs, confirmed by ultrasonography and subsequent dissection. Other locations did not correspond to nerves sites. Transcutaneous thresholds were higher than surgical exposed ones to produce a consistent and satisfactory EMG response. TSE recorded solely in location No. 5 with amplitude values 256-9 μV. It was not possible to stimulate and monitor the RLN and VN after neck CO₂ insufflation. Conclusion: Transcutaneous C-IONM is unfeasible for endoscopic thyroidectomy.

Application of Continuous Intraoperative Neuromonitoring During VATS Lobectomy for Left Lung Cancer to Prevent Recurrent Laryngeal Nerve Injury

We applied continuous intraoperative neuromonitoring (CIONM) during video-assisted thoracoscopic surgery (VATS) lobectomy for left lung cancer and evaluated its safety and usefulness. An electrode was attached to a double-lumen tube, and placed at vocal cord level to detect the EMG signal evoked by vocal cord movement. Before 4 L lymph node dissection, an automatic periodic stimulation device was applied to the vagus nerve to stimulate vagus nerve continuously. Surgery was suspended if the amplitude decreased lower than the threshold and was resumed when the amplitude recovered. Ten patients (6 male, 4 female) were enrolled. CIONM was successfully performed in all patients without technical failure, and there was no hemodynamic instability. Amplitude decreased below the threshold in four patients. One patient did not recover amplitude and experienced transient vocal cord palsy. In the three other patients, the amplitude recovered above the threshold and no vocal cord palsy occurred. The six patients who did not exhibit amplitude decrease experienced no vocal cord palsy. Our results suggest that CIONM may be applied safely for VATS left lobectomy and may be used to predict postoperative vocal cord function. This approach may be helpful to prevent RLN injury during VATS left lobectomy.

Efficacy of continuous neuromonitoring in thyroid surgery: preliminary report of a single-center experience

Background

The continuous intraoperative nerve monitoring (CIONM) technique seems to be acknowledged as a useful tool to prevent impending nerve injury, because it constantly provides valuable real-time information. Aim of the study is to evaluate the impact of the CIONM technique on functional outcome i.e., recurrent laryngeal nerve (RLN) palsy, compared to the traditional surgical procedure.

Methods

From January to December 2016, 197 patients who underwent thyroid surgery were included in this retrospective study: 94 patients had CIONM procedure and 103 traditional technique, according to the order of the operating room list.

Results

A total of 8 patients showed a damage to left or right vocal cord: 3 patients after CIONM procedure, and 5 patients after traditional surgical procedure. After matching for propensity score, 188 patients were eventually considered and 7 RLN palsy were identified: 3 in CIONM and 4 in traditional surgical procedure. The analysis performed on the matched propensity score sample showed a non-significant difference between the two procedures.

Conclusions

In our experience no significant differences in functional outcomes were found between the use of CIONM and the standard technique.

Safety and feasibility of a novel recurrent laryngeal nerve monitoring technique

OBJECTIVES/HYPOTHESIS

Continuous intraoperative nerve monitoring (CIONM) during thyroidectomy is promising technology that may reduce the incidence of recurrent laryngeal nerve (RLN) injuries. However, the current technique for CIONM, in which a stimulating probe is placed on the vagus nerve, has not been widely adopted because of concerns regarding its invasiveness and safety. A new method with the lead positioned on the RLN may overcome these objections and promote greater adoption of CIONM. This study was conducted to serve as the first step in determining the safety and feasibility of an RLN-based CIONM approach.

STUDY DESIGN

Case series with planned data collection.

METHODS

Fifty patients scheduled to undergo thyroidectomy were enrolled. In all cases, after identification of the RLN, a lead designed for CIONM was placed on the nerve. The lead was then left in place for a minimum of 2 minutes, and CIONM data were recorded. Laryngeal electromyographic (EMG) characteristics were assessed just before the lead was placed on the RLN and after it was removed. Pre- and postoperative fiberoptic laryngoscopy was performed to assess vocal cord function in all patients.

RESULTS

In 49 patients (98%), the probe was successfully positioned on the RLN, and CIONM data were generated. On average, 1.4 attempts per patient were required to properly place the lead. No accidental dislodgements of the lead occurred during the experiments. No patients demonstrated significant EMG changes from baseline after manipulation and stimulation of the RLN. The average CIONM time was 175.7 s (range, 138-212 s), and the average CIONM amplitude and latency were 675.2 µV (range, 211.0-1405.2 µV) and 1.8 ms (1.25-1.9), respectively. All patients had normal bilateral vocal cord function preoperatively and at the first postoperative visit.

CONCLUSIONS

This study demonstrates the apparent safety and viability of a CIONM technique using a lead placed directly on the RLN. Future investigations are warranted of this promising method, which may promote more widespread adoption of CIONM during thyroidectomy to reduce RLN injuries.

LEVEL OF EVIDENCE

4 Laryngoscope, 2018.

Modification of the Surgical Strategy for the Dissection of the Recurrent Laryngeal Nerve Using Continuous Intraoperative Nerve Monitoring

BACKGROUND

The aim of this study was to describe first experiences and changes in management using continuous intraoperative neuromonitoring (C-IONM) in thyroid and parathyroid surgery.

METHOD

Retrospective analysis of patients who underwent surgery with C-IONM since 2012. Surgical maneuvers were modified when electrophysiologic events occurred. Patients with persistent loss of signal (LOS) underwent postoperative laryngoscopy.

RESULTS

One hundred and one patients (of 1586 neck surgeries) were included and 19 had events: In 13 these were temporary (resolved before end of surgery) and led to intraoperative modifications in surgical approach; in all cases traction was released, and in 8, recurrent laryngeal nerve (RLN) approach was changed [superior approach (2), inferior approach (2), both (4)]. Six patients had persistent LOS (5.9%, present at end of procedure), with RLN palsy (RLNP) on postoperative day 1: In three, LOS occurred at electrode placement on the vagus nerve, leading to distal placement of the electrode allowing ipsilateral dissection under continuous monitoring; all three had complete recovery at 6 months. In the three other patients, LOS occurred on the RLN: one probable thermal, one traction lesion and one accidental section of the anterior RLN branch. The RLN recovered within 6 months in two patients, and in the third, RLNP persisted after 6 months (1/101 = 1%).

CONCLUSION

C-IONM provides real-time evaluation of the RLN function, allowing for adaptation of surgical maneuvers to prevent RLNP. It seems particularly useful in difficult cases like redo neck surgery, invasive thyroid cancer and intrathoracic or large goiter. Care should be given at electrode placement on the vagus nerve.

Continuous vagal monitoring value in prevention of vocal cord paralysis following thyroid surgery

OBJECTIVES/HYPOTHESIS

Continuous intraoperative neuromonitoring (CIONM) of the vagus nerve was proposed to obtained frequent repetitive electromyography (EMG) data to recognize early change in intraoperative function of the recurrent laryngeal nerve. We examine our initial experience using this technology.

STUDY DESIGN

Retrospective review.

METHODS

Data for all patients who underwent neck surgery by a single surgeon at a North American institution over a 5-year period were reviewed. CIONM was used in cases with possible higher risk of traction injury and according to surgeon preference. In these cases, stretch injury was established by warning alarm with threshold of ≥50% reduction in amplitude and/or ≥ 10% increase in latency. Preoperative and postoperative direct laryngoscopy was performed for all patients.

RESULTS

A total of 879 endocrine neck surgeries were performed. CIONM was used to monitor 455 recurrent laryngeal nerves (RLNs) in 344 (39.1%) surgeries. An automatic periodic stimulation (APS) alarm detected impending nerve injury in 33 (9.6%) cases by 64.9% ± 12.7% decrease in amplitude and by 27.3% increase in latency in one case. A total loss of signal (LOS) was detected in 15 (4.36%) cases. The immediate release of causative retraction successfully preserved the nerves in all cases with impending injury; however, there was no improvement in the LOS cases. Other than the cases with LOS, postoperative laryngoscopy showed normal vocal cord function in all cases.

CONCLUSIONS

APS technology is safe, feasible, and helpful in approximately 10% of cases in our series, which developed nascent neurapraxia adverse EMG changes associated with intraoperative RLN stretch that could be reversed intraoperatively.

LEVEL OF EVIDENCE

4. Laryngoscope, 128:2429-2432, 2018.

Opportunities and challenges of intermittent and continuous intraoperative neural monitoring in thyroid surgery

The number of thyroid operations and there radically continues to rise in the western hemisphere, bringing prevention of recurrent laryngeal nerve (RLN) palsy to the fore. Overall, the incidence of RLN palsy is fairly low but continues to prompt litigation for malpractice. In an effort to diminish transient, and more importantly permanent, RLN palsy rates, intraoperative neuromonitoring (IONM) has been advocated as a risk minimization tool. Recent meta-analyses of studies, many of which were limited by poor study design and the sole use of intermittent nerve stimulation, were unable to demonstrate superiority of IONM over mere anatomic RLN dissection. This is where continuous IONM (CIONM) comes into play: this technology enables the surgeon to (I) identify impending nerve injury as it unfolds; (II) release distressed nerves by reversing causative surgical maneuvers; and (III) verify functional nerve recovery after intraoperative loss of the electromyographic signal. Despite this superiority, CIONM is not devoid of methodological limitations, which need to be accounted for. This review summarizes the current key achievements of IONM; outlines opportunities for improvement regarding clinical implementation; and suggests areas of future research in this rapidly evolving field.

Application of transoral continuous intraoperative neuromonitoring in natural orifice transluminal endoscopic surgery for thyroid disease: a preliminary study

BACKGROUND

The novel concept of continuous intraoperative neuromonitoring (Cont-IONM) through stimulation of the vagal nerve has been used in thyroidectomies to prevent imminent injury of the recurrent laryngeal nerve (RLN). This article reports on this technology and the results of using transoral Cont-IONM in natural orifice transluminal endoscopic surgery for thyroid disease.

METHODS

Cont-IONM of the RLN was achieved through automatic cyclical stimulation of the vagal nerve using a C2 monitor and delta stimulating electrode. During the operation, three vestibular incisions were made, and the stimulating electrode was transorally inserted, with its cable line lying outside the trocar. The vagal nerve was gently dissected, looped, and then enveloped by the electrode cuff. Electromyography (EMG) of the vocalis muscle was performed, and the alarm was set to activate when the EMG amplitude reduced by 50% and latency was prolonged by 10%. Demographic data and outcome variables, including incremental time required to achieve Cont-IONM, were obtained.

RESULTS

A total of 20 patients (28 nerves at risk) undergoing a transoral endoscopic thyroidectomy vestibular approach were enrolled in this study. All Cont-IONM procedures were successfully completed. In all patients, the stimulation was set at 0.7 milliamps every 1 s, and Cont-IONM use was unassociated with any untoward neural, cardiovascular, or gastrointestinal sequelae. On average, the ipsilateral Cont-IONM procedure required 10.33 ± 2.57 min to complete. Except for one instance, no significant problems occurred with electrode displacement. In one patient, a combined EMG event occurred, which improved after releasing the thyroid retractor, and the patient had no vocal cord paralysis postoperatively.

CONCLUSION

Cont-IONM is feasible and safe to use during transoral endoscopic thyroidectomies and may assist in the early detection of adverse EMG changes, thereby preventing paralysis of the RLNs.

Continuous intraoperative neural monitoring of the recurrent nerves in thyroid surgery: a quantum leap in technology

The continuous intraoperative neural monitoring (CIONM) technique is increasingly acknowledged as a useful tool to recognize impending nerve injury and to abort the related manoeuvre to prevent nerve injury during thyroid surgery. CIONM provides valuable real-time information constantly, which is really useful during complex thyroid surgeries especially in the settings of unusual anatomy. Thus, CIONM overcomes the key methodological limitation inherent in intermittent nerve monitoring (IINOM); which is allowing the nerve to be at risk in between the stimulations. The clinically important combined electromyographic (EMG) event, indicative of impending recurrent laryngeal nerve (RLN) injury, prevents the majority of traction related injuries to the anatomically intact RLN enabling modification of the causative surgical manoeuvre in 80% of cases. These EMG changes can progress to loss of EMG signal with postoperative vocal cord palsy (VCP) if corrective action is not taken. As a further extension, CIONM also helps to identify intraoperative functional nerve recovery with restitution of amplitude to ≥50% of initial baseline; this allows continuing of resection of contralateral side. CIONM facilitates for early corrective action before permanent damage to the nerve has been done. CIONM is a recent but rapidly evolving technique, constantly being refined by various studies focusing on improvement in its implementation and interpretation, as well as on the elimination of the technical snags.

Intraoperative neural monitoring in thyroid surgery: lessons learned from animal studies

Recurrent laryngeal nerve (RLN) injury remains a significant morbidity associated with thyroid and parathyroid surgery. In the past decade, surgeons have increasingly used intraoperative neural monitoring (IONM) as an adjunct technique for localizing and identifying the RLN, detecting RLN injury, and predicting the outcome of vocal cord function. In recent years, many animal studies have investigated common pitfalls and new applications of IONM. For example, the use of IONM technology in animal models has proven valuable in studies of the electrophysiology of RLN injury. The advent of animal studies has substantially improved understanding of IONM technology. Lessons learned from animal studies have immediate clinical applications in establishing reliable strategies for preventing intraoperative RLN injury. This article gives an overview of the research progress on IONM-relevant animal models.

Intraoperative monitoring of the recurrent laryngeal nerve by vagal nerve stimulation in thyroid surgery

The aim of the present study was to evaluate the thyroarytenoid muscle response during bilateral thyroid surgery using vagal nerve stimulation. 195 patients (390 nerves at risk) underwent a total thyroidectomy. The recurrent laryngeal nerve's function was checked by analyzing the amplitude and the latency of the thyroarytenoid muscle's responses after a vagal nerve's stimulation (0.5 and 1 mA) using the NIM3 Medtronic system. All patients were submitted to preoperative and postoperative laryngoscopy. 20 patients get no thyroarytenoid muscle response to the vagal nerve stimulation, and 14 postoperative recurrent laryngeal nerve palsies were confirmed (3.8 %). Two palsies were present after 6 months (0.51 %). All the patients with muscle's response have normal mobility vocal fold. The test sensitivity was 100 % and the test specificity was 98 %. Physiologically, the mean latencies of the muscular potentials for the right RLN were, respectively, 3.89 and 3.83 ms (p > 0.05) for the stimulation at 0.5 and 1 mA. The mean latencies for the left RLN were, respectively, 6.25 and 6.22 ms for the stimulation at 0.5 and 1 mA (p > 0.05). The difference of the latencies between the right and the left nerve was 2.30 ms (1.75-3.25 ms) with a stimulation of 0.5 or 1 mA (p < 0.05). Thyroarytenoid muscle's response via a vagal nerve stimulation showed a functional asymmetry of the laryngeal adduction with a faster right response. Surgically, this method can predict accurately an immediate postoperative vocal folds function in patients undergoing a bilateral thyroid surgery.

Continuous intraoperative neuromonitoring in thyroid surgery: Safety analysis of 400 consecutive electrode probe placements with standardized procedures

BACKGROUND

Continuous intraoperative neuromonitoring (C-IONM) is a new technology and it is appropriate to analyze its safety.

METHODS

C-IONM was performed according to a standardized technique to control any adverse events and electrode positioning issues.

RESULTS

Four hundred vagal nerve dissections were analyzed considering vagal nerve diameter, mean time effort for C-IONM probe positioning, and electrode dislocation rate. A significant superior dislocation rate in case of: (a) when a 3 mm automatic periodic stimulating (APS) electrode size was used in a vagal nerve diameter <2 mm; (b) anterior access; and (c) vagal nerve A subtype in relation (p < .05). No related additional local or systemic morbidity was registered in this series. There was a statistically significant positive relationship between increased diameter of vagal nerve and increased electromyography (EMG) amplitude (p = .03). There was also a significant increase of amplitude between initial and final vagal nerve stimulation in uneventful cases (p = .02).

CONCLUSION

We analyzed the technical issues to achieve improved vagal nerve critical view of safety dissection, stimulation, and C-IONM probe placement. © 2015 Wiley Periodicals, Inc. Head Neck 38: E1568-E1574, 2016.

Vocal cord paralysis predicted by neural monitoring electrophysiologic changes with recurrent laryngeal nerve compressive neuropraxic injury in a canine model

BACKGROUND

Recurrent laryngeal nerve (RLN) injury is a known complication of thyroid/parathyroid surgery. Intraoperative nerve monitoring (IONM) has been used to gain more information regarding the functional status of the RLN intraoperatively; however, the electromyography (EMG) parameters of RLN after nontransection neuropraxic compressive injury remain unknown.

METHODS

We developed a canine model to identify IONM EMG correlates of postoperative vocal cord paralysis (VCP) using a standardized method to simulate surgical RLN compression sufficient to cause VCP.

RESULTS

Compression nerve injury decreased EMG amplitude and increased EMG latency, with a 60% increase in RLN threshold stimulation compared to preinjury values. If RLN amplitude decreases by 80% with an absolute amplitude of 300 μV or less in combination with a latency increase of 10% or more, then nerve injury and associated VCP is likely.

CONCLUSION

These results may help surgeons to prognosticate postoperative neural function and intraoperative decision-making regarding contralateral thyroid surgery. © 2015 Wiley Periodicals, Inc. Head Neck 38: E1341-E1350, 2016.

Postoperative vocal fold palsy in patients undergoing thyroid surgery with continuous or intermittent nerve monitoring

Background

Continuous monitoring of electromyographic (EMG) amplitudes of the vocal muscles detects impending injury of the recurrent laryngeal nerve (RLN) during thyroid operations earlier than intermittent EMG monitoring. This may alert the surgeon to stop a manoeuvre causing stretching or pressure on the RLN, with better recovery of nerve function.

Methods

Patients with intact preoperative RLN function who underwent thyroid surgery for benign disease between January 2011 and September 2014 under continuous intraoperative nerve monitoring (CIONM) or intermittent intraoperative nerve monitoring (IIONM) were included in this observational study conducted at a tertiary surgical centre. For CIONM, combined EMG events indicative of imminent nerve injury were defined as an EMG amplitude decrease of 50 per cent or more and a latency increase of 10 per cent relative to baseline values. The rates of early and permanent palsy for the two groups of patients were compared.

Results

There were 1526 patients, 788 of whom (1314 nerves at risk) underwent thyroid surgery using CIONM and 738 (965 nerves at risk) had IIONM. With the use of CIONM, 63 (82 per cent) of 77 combined events were reversible during the operation. No permanent vocal fold palsy occurred with CIONM, whereas four unilateral permanent vocal fold palsies (0·4 per cent) were diagnosed after IIONM (P = 0·019).

Conclusion

Operation with CIONM resulted in fewer permanent vocal fold palsies compared with IIONM after thyroid surgery in patients with benign disease.

Intraoperative neuromonitoring for the early detection and prevention of RLN traction injury in thyroid surgery: a porcine model

BACKGROUND

Operative traction of the thyroid lobe is a necessary component of thyroid surgery. This surgical maneuver can cause traction injury of the recurrent laryngeal nerve (RLN), and this complication has been reported to be the most common mechanism of nerve injury. The goal of this study was to investigate the electromyographic (EMG) signal pattern during an acute RLN traction injury and establish reliable strategies to prevent the injury using intraoperative neuromonitoring (IONM).

METHODS

Fifteen piglets (30 RLNs) underwent IONM via automated periodic vagal nerve stimulation and had their EMG tracings recorded and correlated with various models of nerve injury.

RESULTS

In the pilot study, a progressive, partial EMG loss was observed under RLN tractions with different tension (n = 8). The changes in amplitudes were more marked and consistent than were the changes in latency. The EMG gradually gained partial recovery after the traction was relieved. Among the nerves injured with electrothermal (n = 4), clamping (n = 1), and transection (n = 1) models, the EMG showed immediate partial or complete loss, and no gradual EMG recovery was observed. Another 16 RLNs were used to investigate the potential of EMG recovery after different extents of RLN traction. We noted the EMG showed nearly full recovery if the traction stress was relieved before the loss of signal (LOS), but the recovery was worse if prolonged or repeated traction was applied. The mean restored amplitudes after the traction was relieved before, during, and after the LOS were 98 ± 3% (n = 6), 36 ± 4% (n = 4), and 15 ± 2% (n = 6), respectively.

CONCLUSION

RLN traction injury showed graded, partial EMG changes; early release of the traction before the EMG has degraded to LOS offers a good chance of EMG recovery. IONM can be used as a tool for the early detection of adverse EMG changes that may alert surgeons to correct certain maneuvers immediately to prevent irreversible nerve injury during the thyroid operation.

Influence of intraoperative neurophysiologic monitoring on the development of surgical dissection techniques

Intraoperative neurophysiologic monitoring (IONM) is essential in the preservation of function of nervous system. IONM is thus becoming the gold-standard method in nerve-sparing surgical procedures. Apart from spine and brain surgery, IONM is essential in significantly reducing morbidity in colorectal surgery, prostate and thyroid surgery, as well as in hip replacement, to name a few. IONM measures weak electric nerve potentials and, therefore, it is easily disturbed by other electromagnetic sources. Surgical dissection techniques and devices interfering with IONM make this technique useless because this is dissection that mainly endangers nerve structures. Therefore, there is a need to take into consideration the influence of various dissection techniques on IONM, and to develop or modify inert techniques that are currently not widely used.

Continuous intraoperative vagus nerve stimulation for identification of imminent recurrent laryngeal nerve injury

BACKGROUND

Conventional intraoperative nerve monitoring, predicated on intermittent stimulation, can predict recurrent laryngeal nerve (RLN) palsy only after the damage has been done.

METHODS

Fifty-two patients (52 nerves at risk) who underwent continuous intraoperative nerve monitoring (CIONM) for thyroid surgery via vagus nerve stimulation had their electromyographic (EMG) tracings recorded and correlated with surgical maneuvers and postoperative RLN function.

RESULTS

There was 1 imminent loss of signal (LOS) with intraoperative signal recovery and there were 4 losses of signal with corresponding unilateral transient RLN palsy. When EMG amplitude decreased >50% and EMG latency increased >10%, LOS and postoperative RLN palsy were noted in 4 of 8 patients (50%) who had multiple combined events. In 9 of 13 patients (70%) who developed adverse EMG changes, modification of the causative surgical maneuver resulted in recovery of those EMG changes and aversion of impending RLN palsy.

CONCLUSION

CIONM reliably signaled impending nerve injury, enabling immediate corrective action.

Neuromonitoring in thyroid surgery

PURPOSE OF REVIEW

Laryngeal nerve injuries are among the most important complications of thyroidectomy. Recently, the use of neuromonitoring has been increasingly employed in order to predict and document nerve function at the end of thyroidectomy.

RECENT FINDINGS

There is much controversy in recent studies concerning neuromonitoring in thyroid surgery. Some authors believe that the method does not bring any additional reduction in the paralysis rate of the laryngeal nerves. Other researchers defend its use only in selected cases and in very specific situations. Finally, some much respected surgeons advocate the routine use of neuromonitoring in all thyroidectomies.

SUMMARY

In this review, we try to present relevant recent publications dealing with this still controversial subject, emphasizing the advantages and disadvantages of neuromonitoring in thyroidectomy.

Loss of the nerve monitoring signal during bilateral thyroid surgery

Background

This study aimed to assess current use of recurrent laryngeal nerve monitoring (RLNM) for bilateral thyroid surgery in Germany. It explored the willingness of surgeons to change strategy after loss of signal (LOS) on the first side of resection.

Methods

Surgical departments in Germany equipped with nerve monitors were asked to complete a structured questionnaire, specifying the number of thyroidectomies done in 2010, and the frequencies of RLNM, vagal stimulation, and electromyographic (EMG) recording before and after thyroidectomy. They were also asked about the surgical plan for bilateral goitre after LOS on the first side of resection.

Results

Based on manufacturers' sales data, 1119 (89·1 per cent) of 1256 surgical departments in Germany were equipped with nerve monitors in 2010. A total of 595 departments (53·2 per cent), accounting for approximately 75 per cent of all thyroidectomies in Germany during that year, returned a completed questionnaire. RLNM was used in 91·7–93·5 per cent of thyroidectomies, with the addition of routine vagal stimulation in 49·3 per cent before, and 73·8 per cent after resection. EMG responses to vagal stimulation were recorded in 54·8 per cent before, and 72·5 per cent after resection. Some 93·5 per cent of surgeons changed the resection plan for the other side in bilateral thyroid surgery after LOS had occurred on the first side.

Conclusion

RLNM is now the standard of care during thyroidectomy in Germany. After LOS on the first side of resection in bilateral goitre, more than 90 per cent of respondents declared their willingness to change the resection plan for the contralateral side to avoid the risk of bilateral recurrent laryngeal nerve palsy.

[Signal stability as key requirement for continuous intraoperative neuromonitoring]

BACKGROUND

Postoperative recurrent laryngeal nerve (RLN) palsy is a well-known and dreaded complication of thyroid surgery. Continuous intraoperative neuromonitoring (CIONM) has been developed in order to provide an effective real-time surveillance of the RLN to its full extent and to detect subtle changes in nerve conductivity. A key requirement for a reliable interpretation of CIONM is signal stability.

PATIENTS AND METHODS

In a prospective randomized controlled pilot study 24 patients corresponding to 30 nerves at risk (NaR) were included to compare a newly developed, flexible, saxophone-shaped backstrap electrode for vagal stimulation (16 NaR) to a commercially available CE-marked cylindrical and rigid electrode (14 NaR). Electrode applicability, safety and signal stability were analyzed by assessment of electrode implantation times, stimulation currents, EMG amplitudes and electrode displacement rates.

RESULTS

Implantation and extraction was significantly faster and easier with the saxophone-shaped backstrap electrode. Accidental electrode displacement occurred up to eight times per operation when applying the cylindrical electrode, while a total of two displacements resulted using the backstrap electrode in this study. Stimulation currents necessary for supramaximal RLN stimulation were significantly lower using the newly developed electrode. At the same time, significantly greater stable EMG amplitudes resulted using the new saxophone-shaped electrode. No RLN palsy occurred during the study.

CONCLUSIONS

According to the data, only the saxophone-shaped backstrap electrode provided the signal stability required for CIONM. The closed electrode geometry with isolated contacts for nerve stimulation and defined current entry provide the prerequisites required for reliable continuous intraoperative neuromonitoring.

Continuous intraoperative monitoring of autonomic nerves during low anterior rectal resection: an innovative approach for observation of functional nerve integrity in pelvic surgery

PURPOSE

The aim of this study was to develop a methodological setup for continuous intraoperative neuromonitoring with intent to improve nerve-sparing pelvic surgery.

METHODS

Fourteen pigs underwent low anterior rectal resection. Continuous stimulation of pelvic autonomic nerves was carried out with a newly developed tripolar surface electrode during lateral, anterolateral, and anterior mesorectal dissection. Neuromonitoring was performed under electromyography of the autonomic innervated internal anal sphincter.

RESULTS

Continuous neuromonitoring resulted in significantly increased electromyographic amplitudes of the internal anal sphincter, confirming intact innervation throughout the whole dissection in each animal (median 0.9 μV, interquartile range 0.5; 1.5 vs. median 3.4 μV, interquartile range 2.1; 4.7) (p < 0.001). The median dissection time in each animal was 10 min within a median number of ten (range 8-13) tripolar electric stimulations.

CONCLUSION

The present study is the first to demonstrate that continuous intraoperative monitoring of pelvic autonomic nerves during low anterior rectal resection is feasible.

New Backstrap Vagus Electrode for Continuous Intraoperative Neuromonitoring in Thyroid Surgery

Introduction. Continuous intraoperative neuromonitoring (CIONM) via vagal nerve stimulation allows real-time surveillance of the recurrent laryngeal nerve during thyroid surgery. However, for effective CIONM, subtle changes in recurrent laryngeal nerve conductivity have to be detected. A newly developed stimulation electrode that provides stable nerve stimulation and safe application is presented. Methods. For electrode validation, current distribution was simulated with the finite element method. Mechanical characteristics were assessed through bench testing. Clinical evaluation was initiated with 11 thyroid surgeries. Results. Experimental and clinical results led to the development of a tripolar gold/polyimide electrode mounted onto a backstrap-shaped silicone body. It facilitated rapid electrode implantation and extraction (median implantation time 4 ± 19 seconds). Peak extraction force was 570 mN. Median supramaximal stimulation currents were 2.00 ± 0.95 mA and resulted in reliable electromyogram responses (median 3.1 ± 3.0 mV). No intraoperative electrode dislocations occurred, and no postoperative nerve palsy was observed. Conclusion. The new backstrap vagal stimulation electrode meets the requirements for reliable CIONM.