Safety analysis of vagal nerve stimulation for continuous nerve monitoring during thyroid surgery

Place of laryngoscopy and neuromonitoring in thyroid surgery. Recommendations of the AFCE (Association francophone de chirurgie endocrinienne) with the SFE (Société française d'endocrinologie) and the SFMN (Société française de médecine nucléaire)

Preoperative laryngoscopy is mandatory when there is a history of cervical or thoracic surgery, dysphonia, posteriorly developed thyroid carcinoma, or significant lymph node involvement in the central compartment. Postoperative laryngoscopy should be performed for any postoperative dysphonia, swallowing difficulties, respiratory symptoms, or loss of signal during neuromonitoring of the recurrent and/or vagus nerve. Neuromonitoring can be useful in thyroid surgery because it lowers the rate of transient recurrent palsy (RP), although no impact on permanent RP has been demonstrated. It facilitates location of the recurrent nerve. Continuous neuromonitoring of the vagus nerve can, in some situations, allow early detection of a signal drop during dissection near the recurrent nerve.

Evaluation of penehyclidine for prevention of post operative nausea and vomitting in patients undergoing total thyroidectomy under total intravenous anaesthesia with propofol-remifentanil

Backgroud

Postoperative nausea and vomiting (PONV) is one of the most common complications after total thyroidectomy under general anesthesia. Total intravenous anesthesia (TIVA) has been documented to prevent PONV in patients undergoing total thyroidectomy. Penehyclidine, an anticholinergic agent with an elimination half-life of over 10 h, is widely used as premedication to reduce glandular secretion. This study aimed to explore the preventative effects of penehyclidine with propofol-remifentanil-TIVA to single-TIVA on PONV in patients undergoing total thyroidectomy.

Methods

A total of 100 patients scheduled for total thyroidectomy were randomly assigned to either the penehyclidine group (n = 50) or TIVA group (n = 50). Propofol and remifentanil were was used for TIVA in all patients. No patients who received premedication. Patients were administrated with either 5 ml of normal saline or 0.5 mg of penehyclidine soon after anesthesia induction. The incidence of nausea and vomiting, the severity of nausea, the requirement of rescue antiemetics, and adverse effects were investigated during the first 24 h in two time periods (0–2 h and 2–24 h).

Results

The overall PONV incidence during the 24 h after surgery was significantly lower in the penehyclidine group compared with the TIVA group (12% vs 36%, P < 0.005). Besides, the incidence of nausea and the incidence of vomiting were significantly lower in the penehyclidine group compared with the TIVA group at 2–24 h after surgery. However, there was no significant difference between the two groups at 0–2 h after surgery.

Conclusions

Administration of penehyclidine under TIVA with propofol-remifentanil is more effective for prevention of PONV than TIVA alone, especially 2–24 h after total thyroidectomy.

Trial registration

https://www.chictr.org.cn/edit.aspx?pid=132463&htm=4 (Ref: ChiCTR2100050278, the full date of first registration: 25/08/2021).

Intra-operative nerve monitoring and recurrent laryngeal nerve injury during thyroid surgery: a network meta-analysis of prospective studies

PURPOSE

Recurrent laryngeal nerve (RLN) injury is a feared complication of thyroid surgery occurring in 1-5% of cases. The present approaches to RLN preservation include RLN visualization with no nerve monitoring (No-NM), intermittent intra-operative nerve monitoring (I-IONM) and continuous intra-operative nerve monitoring (C-IONM). There is ambiguity as to which of these strategies should be the preferred method of RLN preservation.

METHODS

A systematic review of the PubMed, Embase and the Cochrane Collaboration databases was undertaken with network meta-analysis (NMA) performed according to the PRISMA and Cochrane Collaboration guidelines. A Bayesian NMA was conducted using R packages netmeta with outcomes expressed as odds ratios (ORs) with 95% credible intervals (CrI). Only prospective studies were included.

RESULTS

Eighteen studies met inclusion criteria, including 22,080 patients and 40,642 nerves at risk (NAR). Overall, 23,364 NARs (57.5%) underwent I-IONM, 17,176 (42.3%) No-NM and 98 (0.2%) underwent C-IONM. There were no significant differences between groups regarding the incidence of permanent RLN injury following thyroid surgery (I-IONM vs.No-NM, OR 0.84, 95% CrI 0.55-1.19; C-IONM vs. No-NM, OR 0.44, 95% CrI 0.02-5.00). Pooled analysis showed that IONM (I-IONM or C-IONM) demonstrated a protective effect versus No-NM in reducing the incidence of transient RLN injury (OR 0.75, 95% CI 0.59-0.97, p = 0.03).

CONCLUSIONS

IONM strategies did not significantly reduce the incidence of permanent RLN injury following thyroid surgery. However, the small number of C-IONM NARs limits conclusions that may be drawn. Further well-designed prospective studies will be required to definitively assess the utility of C-IONM.

High intensity focused ultrasound in the therapy of benign thyroid nodules-first German bicentric study with long-term follow-up

PURPOSE

The study evaluated high-intensity-focused ultrasound (HIFU) for benign thyroid nodules in terms of efficiency, complication rate, influence of preablative nodule size, parameters influencing the therapeutic success and hormonal-thyroid-function.

METHODS

Seventy-two patients with 75 nodules were treated with HIFU at 2 centers from 2014-2019. Median nodule volume was 4.4 ml (range 0.33-53). The therapeutic ultrasound probe (EchoPulse THC900888-H) generated 80-90 °C in the target tissue with 87.6-320.3 J per sonication. Nodal volume was measured at baseline and over 12 months after therapy in a retrospective bicentric-study with long-term follow-up. Hormonal-thyroid function (TSH, T3, T4) was measured before and after ablation. Complications were assessed.

RESULTS

Significant volume reduction (p < 0.05 Wilcoxon-signed-rank test) of thyroid nodules was 38.98% at 3 months, 37.32% at 6 months, 61.54% at 9 months and 60.66% at 12 months. Volume reduction of nodules <3 ml did not differ significantly from nodules >3 ml (p > 0.05 Mann-Whitney test). At 3 months solid nodules had a significant volume reduction of 52.08%, complex nodules of 32.57%, nodules treated under regional anesthesia of 33.07% and under general anesthesia of 49.47%. Hormonal-thyroid function was not influenced significantly by HIFU therapy (p > 0.05 Wilcoxon-signed-rank test). Complication rate was 3.8%. No long-term complications occurred.

CONCLUSION

Significant volume reduction of thyroid nodules up to 12 months after HIFU was shown. All complications were reversible. Therapy was more efficient in solid than complex nodules and in nodules treated under general anesthesia than with regional anesthesia. Hormonal-thyroid-function was not affected.

TRIAL REGISTRAFTION NUMBER

2020-1728-evBO. Date of registration: 16.06.2020. Agency: Ethik-Kommission bei der Landesäztekammer Hessen.

Meta-analysis on continuous nerve monitoring in thyroidectomies

In the last decade, the introduction of continuous intraoperative recurrent laryngeal nerve (RLN) monitoring (C-IONM) has enabled the operator to verify the functional integrity of the vagus nerve-recurrent laryngeal nerve (VN-RLN) axis in real-time. We aim to present the current evidence on C-IONM utility for thyroid surgery by conducting the first meta-analysis on this technique. A systematic review of literature was conducted by two independent reviewers via Ovid in the Medline, EMBASE, and Cochrane reviews databases. The search was limited to human subject research in peer-reviewed articles of all languages published between Jan 1946 and April 2020. Medical subject headings (MeSH) terms utilized were thyroid surgery, thyroidectomies, recurrent laryngeal nerve, vagal nerve, monitor, and stimulation. Thirty-eight papers were identified from Ovid, another six papers were identified by hand-search. A random effect meta-analysis was performed with assessment of heterogeneity using the I² value. A total of 23 papers that investigated the use of continuous vagal nerve monitoring during thyroid surgery were identified. The proportion of nerves at risk (NAR) with temporary RLN paralysis postoperation was 2.26% (95% CI: 1.6-2.9, I²  = 37). The proportion of NAR with permanent RLN palsy postoperation was 0.05% (95% CI: 0.08-0.2, I²  = 0). In this meta-analysis, there is one case of temporary vagal nerve paralysis secondary to VN electrode dislodgement, and a case of hemodynamic instability manifested in bradycardia and hypotension in the initial phase of surgery shortly after calibration. C-IONM is a safe and effective means by which RLN paralyses in thyroid surgery can be reduced.

Tensile strength analysis of automatic periodic stimulation for continuous intraoperative neural monitoring in a piglet model

Continuous intraoperative neural monitoring (C-IONM) during thyroid surgery is a useful tool for preventing recurrent laryngeal nerve (RLN) injury. The present study aims to analyze the tensile strength tolerance of C-IONM electrodes on the vagal nerve (VN). A C-IONM wire was enclosed in a hand-held tensile testing system. The probe displacement on the VN was continuously monitored by positioning a second probe far-up/proximally in a piglet model, and an automatic periodic stimulation (APS) accessory was used. The 3-mm and 2-mm APS accessory has a mean tensile strength of 20.6 ± 10 N (range, 14.6–24.4 N) and 11.25 ± 8 N (range, 8.4–15.6 N), respectively (P = 0.002). There was no difference between bilateral VNs. The mean amplitude before and during electrode displacement was 1.835 ± 102 μV and 1.795 ± 169 μV, respectively (P = 0.45). The mean percentage of amplitude decrease on the electromyography (EMG) was 6.9 ± 2.5%, and the mean percentage of latency increase was 1.9 ± 1.5%. No significant amplitude reduction or loss of signal (LOS) was observed after > 50 probe dislocations. C-IONM probe dislocation does not cause any LOS or significant EMG alterations on the VN.

Continuous intraoperative neuromonitoring (cIONM) in head and neck surgery-a review

Although the history of intraoperative neuromonitoring (IONM) dates back to the 19th century, the method did not evolve further than the mere differentiation of nerves until recently. Only the development of continuous IONM (cIONM) has allowed for non-stop analysis of excitation amplitude and latency during surgical procedures, which is nowadays integrated into the software of almost all commercially available neuromonitoring devices. The objective of cIONM is real-time monitoring of nerve status in order to recognize and prevent impending nerve injury and predict postoperative nerve function. Despite some drawbacks such as false-positive/negative alarms, technical artefacts, and rare adverse effects, cIONM remains a good instrument which is still under development. Active (acIONM) and passive (pcIONM) methods of cIONM are described in literature. The main fields of cIONM implementation are currently thyroid surgery (in which the vagal nerve is continuously stimulated) and surgery to the cerebellopontine angle (in which the facial nerve is either continuously stimulated or the discharge signal of the nerve is analyzed via pcIONM). In the latter surgery, continuous monitoring of the cochlear nerve is also established.

[Continuous intraoperative neuromonitoring (cIONM) in head and neck surgery-a review. German version]

Obwohl die Geschichte des intraoperativen Neuromonitorings (IONM) bereits in das 19. Jahrhundert zurückdatiert werden kann, hat sich diese Methode bis vor Kurzem nicht von der reinen Differenzierung des Nervs weiterentwickelt. Erst das kontinuierliche IONM (cIONM) ermöglichte die durchgehende Analyse der Reizamplituden und -latenzen, welche mittlerweile ebenfalls in die Software gängiger Monitoringsysteme integriert wurde. Zielsetzung des cIONM ist ein Real-Time-Monitoring des Nervenstatus während des Eingriffs, um so drohende Nervenverletzung erkennen und verhindern zu können und die postoperative Funktion des Nervs vorhersehbar zu erhalten. Trotz einiger Nachteile wie falsch-positiver oder -negativer Alarme, technischer Artefakte und seltener Nebenwirkungen bleibt das cIONM ein gutes Hilfsmittel, das noch weiterentwickelt wird. In der Literatur sind sowohl aktive (acIONM) als auch passive (pcIONM) Reiz- und Ableitmethoden des cIONM beschrieben. Derzeit gängige Anwendungsgebiete des cIONM umfassen die Schilddrüsenchirurgie mit der kontinuierlichen Stimulation des N. vagus sowie die Chirurgie des Kleinhirnbrückenwinkels (KHBW) mit dem Monitoring des N. facialis; hierbei werden neben kontinuierlicher Stimulation auch die Entladungsmuster des Nervs analysiert. Des Weiteren ist in die Chirurgie des KHBW das kontinuierliche Monitoring des Hörnervs etabliert.

Continuous intraoperative neuromonitoring for thyroid cancer surgery: A prospective study

Objective

We evaluated the utility of continuous intraoperative neuromonitoring (CIONM) during surgery for thyroid cancer (TC) in an educational university hospital.

Study Design

Prospective observational study.

Methods

During the period April 2016 to March 2017, 43 patients who underwent standardized surgery with CIONM were prospectively included: 5 men and 38 women, 24–87 years old (median 52 years); 23 lobectomies and 20 total thyroidectomies with node dissection were conducted. Thirty‐six operations were performed by a supervising surgeon, and seven were performed by trainees.

Results

Temporal vocal cord paresis (VCP) was identified in 9 of 63 nerves at risk (14.3%) by postoperative laryngoscopy. VCP was not related to clinical factors including the surgeon's experience or the severe nerve stress demonstrated by CIONM. A significant relation only between VCP and loss of signal (LOS) was demonstrated (P = .002). The recovery of VCP was rapid (<1 month) in patients with global injury even when LOS was demonstrated, but was prolonged in patients demonstrating obvious segmental nerve injury and LOS.

Conclusion

The present standard protocol of CIONM was useful to some extent to protect prolonged VCP, but not enough to detect every nerve stress causing VCP during TC surgery. On the other hand, CIONM is a promising method that could contribute surgical education at training hospitals enabling the instant confirmation of the procedure safely.

Levels of Evidence

3b

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.

Complications Following Radiofrequency Ablation of Benign Thyroid Nodules: A Systematic Review

Objective:

This systematic review examined whether radiofrequency ablation (RFA) is a safe treatment modality for benign thyroid nodules (BTNs).

Data Sources:

PubMed, Embase, and the Cochrane Library database were searched for articles that (a) targeted human beings and (b) had a study population with BTNs that were confirmed by fine-needle aspiration cytology and/or core needle biopsy.

Study Selection:

Thirty-two studies relating to 3409 patients were included in this systematic review.

Results:

Based on literatures, no deaths were associated with the procedure, serious complications were rare, and RFA appears to be a safe and well-tolerated treatment modality. However, a broad spectrum of complications offers insights into some undesirable complications, such as track needle seeding and Horner syndrome.

Conclusions:

RFA appears to be a safe and well-tolerated treatment modality for BTNs. More research is needed to characterize the complications of RFA for thyroid nodules.

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 Neuromonitoring Study Using Pigs for the Prevention of Mechanical Recurrent Laryngeal Nerve Injury in Esophageal Surgery

PURPOSES

During esophageal surgery, clamping injury and injury associated with the use of energy devices are common mechanisms underlying intraoperative recurrent laryngeal nerve (RLN) damage. Recently, intraoperative neuromonitoring (IONM) has been applied to prevent RLN injury. This study was aimed at investigating the changes in the EMG signals associated with clamping injury of the RLN caused by picking up of the nerve with tweezers in domestic pigs.

METHODS

Six domestic pigs (12 RLNs) underwent continuous IONM (CIONM) by our original automated periodic vagal nerve stimulation method.

RESULTS

Our system can be used safely and accurately. The signals showed a decrease of the amplitude when the RLN was picked up and closed slowly by the double-action Maryland with jaw covers. If the clamp was released before the signal amplitude decreased to 50% of the baseline, the signal showed gradual recovery to the baseline in 12 ± 3 minutes.

CONCLUSION

Although there were limitations in our study using domestic pig, including the small sample size, our results are expected to contribute to a decrease in the incidence of RLN damage during esophageal surgery.

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.

The weepy nerve-different sensitivity of left and right recurrent laryngeal nerves under tensile stress in a porcine model

PURPOSE

Recurrent laryngeal nerve palsy in thyroid surgery is still a threatening complication. Our aim was to analyze the impact of prolonged tensile stress on the recurrent laryngeal nerve (RLN) in an animal model using continuous intraoperative neuromonitoring (C-IONM).

METHODS

Constant tensile stress was applied to left and right RLNs in 20 pigs (40 RLN). In a pilot study, five animals were subjected to a tensile force of 0.34 ± 0.07 N for 10 min and changes in amplitude were documented using C-IONM. In the main study, a force of 1.2 N was applied until the signal amplitude was reduced by 85 %, in 15 pigs. Nerve conductivity was analyzed by threshold current measurements.

RESULTS

Good correlation was found between stress and amplitude decrease in the pilot study as well as between signal decrease and duration of trauma in the main study. Great variations were found inter- and intra-individually. These variations were most prominent at 85 % signal reduction (median 36 min, range 0.3-171 min). There was no side specificity (left 0.3-171 min, right 0.3-168 min, respectively, p = 0.19). However, in each individual animal, there was a sensitive (0.3-98.9 min) and less sensitive nerve (26.8-171 min). These differences became highly significant at 85 % of signal reduction (p = 0.008), where the vulnerability is 1.4 to 146.4 times higher on one side (mean 4.3).

CONCLUSIONS

Our study demonstrates the presence of a sensitive RLN that was 4.3 times more vulnerable than the contralateral nerve (range 1.4-146.4 times, p = 0.008). Thus, the right and the left nerves cannot be assumed to be of equal sensitivity to trauma. In our data, the more sensitive nerve does not occur predominantly on one side and was named the "weepy nerve."

Cardiac arrest with vagal stimulation during intraoperative nerve monitoring

BACKGROUND

Intraoperative neuromonitoring (IONM) is widely used during thyroid surgery. During both intermittent and continuous IONM stimulation of the vagus nerve is performed. This has previously been reported to be safe.

METHODS

We present our findings based on the case reports of 2 patients.

RESULTS

IONM of the recurrent laryngeal nerve (RLN), following the standards of the International Neuromonitoring Study Group, was conducted in 2 patients, one undergoing thyroid surgery and the second parathyroid surgery. In both cases, after dissection and stimulation of the vagus nerve on 1 mAmp, the patients became asystolic. Resuscitation efforts were successful in both patients.

CONCLUSION

These 2 cases demonstrate that stimulation of the vagus nerve during IONM can lead to profound cardiac events. Consideration should be given to these potential complications when utilizing IONM. © 2016 Wiley Periodicals, Inc. Head Neck 38: E2419-E2420, 2016.

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.

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.

Recurrent laryngeal nerve monitoring during thoracoscopic esophagectomy

INTRODUCTION

There have been several reports on the feasibility and curability of thoracoscopic esophagectomy, which may reduce injury to the thoracic cage and decrease the invasiveness of surgery. Although the recurrent laryngeal nerve (RLN) is identified and kept intact during operations, RLN palsy sometimes occurs. Currently, surgical aides, including intraoperative neurological monitoring, are being utilized to avoid RLN injury during thyroid surgery. This system is utilized during thoracoscopic esophagectomy in the prone position.

PATIENTS AND METHODS

Seven consecutive patients (six men, one woman; age range 62-74 years; mean 68 years) were included. Patients underwent general anesthesia and were intubated using the NIM TriVantage™ electromyography (EMG) tube. One-lung ventilation was performed with an endobronchial blocker. Thoracoscopic esophagectomy was performed in the prone position. The nerve stimulator was calibrated to 0.5 mA, and after the RLN was visually identified it was subsequently stimulated, which also confirmed normal machine functioning. In some situations, in the absence of a response, stimuli were increased to 1.0 mA and then 2.0 mA.

RESULTS

Intraoperatively, all seven patients had their nerve signals monitored. In one case, a nerve signal disappeared after complete lymph node dissection along the left RLN. This system could identify the site of injury, and the thoracoscopic magnified view allowed the disrupted point to be located precisely. When we checked VTR after surgery, the source of injury was one point tension of the nerve pulled by fiber during lymph node dissection.

CONCLUSIONS

Intraoperative RLN monitoring during thoracoscopic esophagectomy in the prone position, with one-lung ventilation performed using the TriVantage™ EMG tube and a bronchial blocker, is technically feasible, easy, and reliable.

Assessment of recurrent laryngeal nerve function during thyroid surgery

INTRODUCTION

There is disparity in the reported incidence of temporary and permanent recurrent laryngeal nerve (RLN) palsy following thyroidectomy. Much of the disparity is due to the method of assessing vocal cord function. We sought to identify the incidence and natural history of temporary and permanent vocal cord palsy following thyroid surgery. The authors wanted to establish whether intraoperative nerve monitoring and stimulation aids in prognosis when managing vocal cord palsy.

METHODS

Prospective data on consecutive thyroid operations were collected. Intraoperative nerve monitoring and stimulation, using an endotracheal tube mounted device, was performed in all cases. Endoscopic examination of the larynx was performed on the first postoperative day and at three weeks.

RESULTS

Data on 102 patients and 123 nerves were collated. Temporary and permanent RLN palsy rates were 6.1% and 1.7%. Most RLN palsies were identified on the first postoperative day with all recognised at the three-week review. No preoperative clinical risk factors were identified. Although dysphonia at the three-week follow-up visit was the only significant predictor of vocal cord palsy, only two-thirds of patients with cord palsies were dysphonic. Intraoperative nerve monitoring and stimulation did not predict outcome in terms of vocal cord function.

CONCLUSIONS

Temporary nerve palsy rates were consistent with other series where direct laryngoscopy is used to assess laryngeal function. Direct laryngoscopy is the only reliable measure of cord function, with intraoperative monitoring being neither a reliable predictor of cord function nor a predictor of eventual laryngeal function. The fact that all temporary palsies recovered within four months has implications for staged procedures.

Intraoperative neurophysiologic monitoring: basic principles and recent update

The recent developments of new devices and advances in anesthesiology have greatly improved the utility and accuracy of intraoperative neurophysiological monitoring (IOM). Herein, we review the basic principles of the electrophysiological methods employed under IOM in the operating room. These include motor evoked potentials, somatosensory evoked potentials, electroencephalography, electromyography, brainstem auditory evoked potentials, and visual evoked potentials. Most of these techniques have certain limitations and their utility is still being debated. In this review, we also discuss the optimal stimulation/recording method for each of these modalities during individual surgeries as well as the diverse criteria for alarm signs.

Neuromonitoring of the laryngeal nerves in thyroid surgery: a critical appraisal of the literature

One of the most significant complication of thyroid surgery is injury of the recurrent laryngeal nerve. Injury of the external branch of the superior laryngeal nerve is a less obvious but occasionally significant problem. Recently, neuromonitoring during thyroidectomy has received considerable attention because of literature encouraging its use, but there is no consensus about its advantages and utility. A critical assessment of the literature on neuromonitoring was conducted in order to define its effectiveness, safety, cost-effectiveness and medical-legal impact. Available data does not show results superior to those obtained by traditional anatomical methods of nerve identification during thyroid surgery. Data about cost-effectiveness is scarce. The literature shows inconsistencies in methodology, patient selection and randomization in various published studies which may confound the conclusions of individual investigations. The current recommendation for use in "high risk" patients should be assessed because definition heterogeneity makes identification of these patients difficult. As routine use of neuromonitoring varies according to geography, its use should not be considered to be the standard of care.

Protective effect of intraoperative nerve monitoring against recurrent laryngeal nerve injury during re-exploration of the thyroid

BACKGROUND

Previous thyroid or parathyroid surgery induces scarring or distorts anatomy, and increases the risk of recurrent laryngeal nerve (RLN) injury for a reoperation. The benefit of intraoperative nerve monitoring (IONM) for re-exploration (a second nerve exploration) and reoperation has not been established.

METHODS

Two hundred and ten patients were given a thyroid or parathyroid reoperation at our hospital between 2001 and 2010. Using IONM, we re-explored 56 patients who had been operated on before June 2007. The injury rate in these patients was compared with that of the 15 patients re-explored without IONM between 2001 and 2006.

RESULTS

Of the 70 nerves that were re-explored using IONM, only one was incidentally injured, significantly fewer than the three injured in the 15 nerves re-explored without using IONM (1.43% vs. 20%, P = 0.0164).

CONCLUSIONS

IONM helped prevent RLN damage when re-exploring nerves during thyroid and parathyroid surgery. We recommend the routine use of IONM in thyroid and parathyroid reoperations.