Interpretation of intraoperative recurrent laryngeal nerve monitoring signals: The importance of a correct standardization

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.

Adverse events in thyroid surgery: observational study in three surgical units with high volume/year

Background

Thyroid surgery, performed for benign or malignant pathologies, is one of the most frequently performed procedures and its frequency has even been increasing in recent years. Postoperative bleeding, recurrent laryngeal nerve (RLN) palsy, associated to dysphonia, dysphagia, dyspnea, and hypoparathyroidism represent the most fearful and common complications. We conducted a multicenter, observational study of retrospectively collected data in three high-volume referral centers, enrolling all patients undergone to thyroid surgery between January 2016 and December 2017 in Parma University Hospital, Cagliari University Hospital and Ferrara University Hospital.

Materials

Patients were divided into five groups, differentiated thyroid carcinoma, medullary thyroid carcinoma, non-toxic benign pathology, hyperfunctioning benign pathology and NIFTP (Non-invasive Follicular Thyroid neoplasm with Papillary-like nuclear features). A follow up at 7 and 30 days was executed, evaluating the onset of paresthesia, dysphonia and dysphagia. A 6-month follow-up was conducted in cases of early complications.

Results

Totally, 1252 patients were eligible for the study: 907 female and 345 male, with a female to male ratio of 2.6:1 and an average age of 53.428. Total thyroidectomy was performed in 1022 cases, lobectomy in 230. After 6 months we recorded paresthesia in 0.5%, dysphonia in 1.8% and dysphagia in 0.5%.

Conclusion

Our study confirms once again that a share of morbidity escapes the possibilities of prediction and control by the operator, depending on patient anamnestic, pathological or anatomical factors.

Intraoperative Neural Monitoring for Early Vocal Cord Function Assessment After Thyroid Surgery: A Systematic Review and Meta-Analysis

Objective This study evaluated the diagnostic accuracies of various forms of intraoperative neural monitoring (IONM) in terms of predicting vocal cord palsy after thyroidectomy. Methods Two authors independently reviewed the six databases (PubMed, the Cochrane database, Embase, the Web of Science, SCOPUS, and Google Scholar) from their dates of inception to March 2021. Intraoperative electromyographic neuromonitoring (IONM) was compared with laryngoscopic detection (the reference method). True-positive, true-negative, false-positive, and false-negative data were extracted from each study. Methodological quality was evaluated using the Quality Assessment of Diagnostic Accuracy Studies ver. 2 tool. Results Twenty-seven prospective or retrospective studies were included. The diagnostic odds ratio for IONM was 152.9623 ([95% confidence interval [75.4249; 310.2085]. The area under the summary receiver operating characteristic curve was 0.966. The sensitivity, specificity, negative predictive value, and positive predictive value were 0.8219 ([0.6862; 0.9069]), 0.9783 ([0.9659; 0.9863]), 0.9943 ([0.9880; 0.9973]), and 0.5523 ([0.4458; 0.6542]), respectively. The correlation between sensitivity and false-positive rate was 0.200, indicating the absence of heterogeneity. Subgroup analysis showed that the diagnostic accuracies of the continuous IONM was higher than those of intermittent IONM, and recent publications (> 2011) was higher than early publication (< 2010). Conclusions As the technology and knowledge of IONM have been accumulated and progressed over the past decades, the predictive value of IONM in postoperative vocal cord palsy has also improved. Moreover, the advances of continuous IONM technology could make a breakthrough in vocal cord evaluation after thyroid surgery.

Efficacy of Transcartilaginous Electrodes for Intraoperative Neural Monitoring During Thyroid Surgery

Objectives.

This study was conducted evaluate the efficacy of electromyography (EMG) using transcartilaginous (TC) electrodes through the thyroid cartilage and perichondrium.

Methods.

We prospectively collected EMG data from intraoperative neuromonitoring (IONM) of 54 nerves at risk in 38 patients during thyroidectomy. We followed standardized IONM procedures in all operations. EMG signals from both endotracheal tube (ET) electrodes and TC needle electrodes were recorded simultaneously. We compared the characteristics of the EMG signals and the efficacy of both methods.

Results.

Significantly higher mean EMG amplitudes were recorded by TC electrodes than by ET electrodes in all four-step procedures (V1-R1-R2-V2, P<0.001). Loss of signal (LOS) occurred in five patients in ET electrodes, but in only two patients in TC electrodes. Postoperative laryngoscopy revealed recurrent laryngeal nerve palsy in the two patients who showed LOS from both the ET and TC electrodes, and vocal cord movement was intact in the other three patients. Therefore, the positive predictive values of LOS in ET and TC electrodes were 40% and 100%, respectively.

Conclusion.

EMG recording using TC needle electrodes is feasible and effective, making it a good alternative technique for IONM.

Early detection of recurrent laryngeal nerve damage using intraoperative nerve monitoring during thyroidectomy

Objective

This study aimed to investigate risk factors for early recurrent laryngeal nerve (RLN) damage during thyroid surgery with intraoperative nerve monitoring (IONM) technology to avoid RLN damage during surgery.

Methods

Data were retrospectively collected from 93 patients who underwent thyroidectomy at Beijing Hospital. All operations were performed by the same surgeon. A four-step procedure of IONM was used during the operation to determine the amplitude and latency of the RLN.

Results

The majority (51.6%) of patients who underwent surgery had thyroid carcinoma. Lymphadenectomy was carried out in 55 (59.1%) patients. A strong association was observed between temporary injury of the RLN and the extent of resection. The risk of temporary injury of the RLN during total thyroidectomy was three times that during right thyroid lobectomy (odds ratio = 3.13). The results of left lobectomy were also different from those of right lobectomy because the RLN was more likely to be damaged during left lobectomy.

Conclusions

Assessment of the amplitude and latency of the RLN can help to assess the integrity of the RLN. The extent of resection affects the functional integrity of the RLN.

Intraoperative nerve monitoring in endocrine surgery: prevalence and reasons for its use in Australia and New Zealand

BACKGROUND

Intraoperative nerve monitoring (IONM) has increasingly been used in thyroid surgery by general, endocrine and head and neck surgeons. The purpose of this paper was to explore the prevalence and reasons for the usage of IONM in endocrine surgery in Australia and New Zealand.

METHODS

A survey was sent to general surgeons registered with the Royal Australasian College of Surgeons involved in endocrine surgery and members of the Australian and New Zealand Endocrine Surgeons. Users were divided into surgeon type, area of work, hospital type and volume of surgery. These data were analysed with univariate and multivariate logistic regression models.

RESULTS

Significant differences in IONM usage levels were observed between endocrine and general surgeons, area of work and volume of surgery performed. Endocrine surgeons are significantly more likely to use IONM than general surgeons. Surgeons who work in tertiary hospitals are more likely to use IONM as compared to those working in district hospitals. Surgeons who perform less than 100 thyroidectomies were more likely to be users of IONM.

CONCLUSION

IONM is not routinely used in thyroid surgery in Australia and New Zealand. The main reasons for the use of IONM given in our study by routine users were to establish familiarity of equipment and medicolegal reasons. Selective users chose as the most common reasons, a documented pre-existing unilateral nerve paresis or a hostile surgical field. Non-users stated that there was conflicting evidence that it improves outcomes and increased costs.

Methodological Quality of Systematic Reviews of Intraoperative Neuromonitoring in Thyroidectomy: A Systematic Review

Importance

Systematic reviews and meta-analyses are considered the best evidence for clinical decision making. Many reviews of intraoperative neuromonitoring (IONM) in thyroidectomy have conflicting results, owing in large part to methodological quality.

Objective

To assess the methodological quality and the causes of heterogeneous results of systematic reviews that compare routine IONM vs visual identification of the recurrent laryngeal nerve (RLN) in patients undergoing thyroidectomy.

Data Sources

A systematic search was performed of MEDLINE (PubMed), Embase, the Cochrane Library, LILACS (Literatura Latino Americana e do Caribe em Ciências da Saúde), Web of Science, and Google from January 1, 1968, through June 30, 2018. Data were analyzed from July 17 to November 30, 2018.

Study Selection

Studies that mentioned performance of a systematic review/meta-analysis during the search period.

Data Extraction and Synthesis

Data including study characteristics, type of patients, numbers of nerves at risk, and temporary and definitive RLN paralysis by group were extracted. Data about methodological characteristics, type of statistical analysis and summary estimator, endorsement of systematic review/meta-analysis guidelines, heterogeneity, publication bias, funding, conflict of interest, and statistical analysis were also recorded. The methodological quality was measured with the AMSTAR2 (A Measurement Tool to Assess Systematic Reviews) tool by 2 independent evaluators.

Main Outcomes and Measures

Methodological quality.

Results

The search identified 13 systematic reviews that included patients who underwent open or minimally invasive thyroidectomy, second operations, and a mixture of low- and high-risk procedures. The mean compliance with the AMSTAR2 overall criteria was 53% (range, 11%-83%); with critical criteria, 71% (range, 50%-94%). The percentage of nerves at risk from RCTs was 4.8%. The mean (SD) crude rate of definitive RLN paralysis was 0.81% (0.22%; median, 0.75% [range, 0.53%-1.30%]) in the monitoring group and 1.14% (0.56%; median, 0.96% [range, 0.57%-2.56%]) in the control group.

Conclusions and Relevance

A substantial number of systematic reviews of IONM in thyroidectomy have conflicting results, but their mean methodological quality is critically low. Design of a systematic review should comply with methodological standards and recommendations to offer relevant and practical information for decision making.

Analysis of neuromonitoring signal loss during retroauricular versus conventional thyroidectomy

OBJECTIVE

Loss of signal (LOS) during intraoperative neuromonitoring (IONM) of robotic or endoscopic thyroidectomy via a retroauricular approach (RAT) and during conventional open thyroidectomy (COT) was investigated to compare the risk of recurrent laryngeal nerve (RLN) injury between the two groups.

STUDY DESIGN

Original article.

METHODS

This is a retrospective case series study performed between May 2014 and September 2016. IONM using the NIM 3.0 system (Medtronic Xomed, Inc., Jacksonville, FL) was used for this study. Pre- and postoperative vocal cord functions were assessed using a flexible laryngoscope. LOS types noted intraoperatively and their associations with postoperative vocal cord palsy (VCP) were evaluated. LOS rate and temporary and permanent VCP rates were compared between the two groups. The surgical events associated with LOS were also documented and analyzed in this study.

RESULTS

In total, 153 patients were recruited, and 111 patients were enrolled in the RAT group; the remaining 42 patients were enrolled in the COT group. No statistically significant differences in intraoperative LOS (P = 0.812) and postoperative VCP rates (early, permanent; P = 0.259 and P = 0.577, respectively) between the two groups were observed. IONM accuracy of predicting postoperative VCP was 99.1% in our case series.

CONCLUSION

On the basis of IONM findings, the risks of injury to RLN were similar between the two groups. Comparison of LOS was an objective method for verifying the novel RAT approach. We applied our IONM protocol and troubleshooting algorithm during RAT with acceptable accuracy, but the international standardized method of IONM is applicable and recommended for reducing false results using vagal nerve stimulation.

LEVEL OF EVIDENCE

3b Laryngoscope, 129:2199-2204, 2019.

Protective Effects of Intraoperative Nerve Monitoring (IONM) for Recurrent Laryngeal Nerve Injury in Thyroidectomy: Meta-analysis

Recurrent laryngeal nerve (RLN) injury is an intractable complication of thyroidectomy. Intraoperative nerve monitoring (IONM) was designed to prevent RLN injury. However, the results concerning the protective effect of IONM on RLN injury are still controversial. We searched all eligible databases from 1980 to 2017. Meta-analysis was performed to evaluate the effect of IONM on RLN injury. Sensitivity analysis was also conducted to check the stability of our results. There were 34 studies included in the analysis. Overall analysis found a significant decrease in total injury (RR = 0.68, 95%CI: 0.55 to 0.83), transient injury (RR = 0.71, 95%CI: 0.57 to 0.88), and permanent injury (RD = −0.0026, 95%CI: −0.0039 to −0.0012) with IONM. Subgroup analysis found IONM played a preventive role of total, transient and permanent injury in patients undergoing bilateral thyroidectomy. IONM also reduced the incidence of total and transient injury for malignancy cases. Operations with IONM were associated with fewer total and transient RLN injuries in operation volume < 300 NARs per year and fewer total and permanent RLN injuries in operation volume ≥ 300 NARs per year. The application of IONM could reduce the RLN injury of thyroidectomy. Particularly, we recommend routine IONM for use in bilateral operations and malignancy operations.

Intraoperative neuromonitoring in thyroid surgery: Is the two-staged thyroidectomy justified?

BACKGROUND

The aim of this study was to evaluate the diagnostic accuracy of intraoperative neuromonitoring (IONM) in predicting postoperative nerve function during thyroid surgery and its consequent ability to assist the surgeon in intraoperative decision making.

MATERIALS AND METHODS

A total of 2365 consecutive patients were submitted to thyroidectomy by the same surgical team. Group A included 1356 patients (2712 nerves at risk) in whom IONM was utilized, and Group B included 1009 patients (2018 nerves at risk) in whom IONM was not utilized.

RESULTS

In Group A, loss of signal (LOS) was observed in 37 patients; there were 29 true positive, 1317 true negative, 8 false positive, and 2 false negative cases. Accuracy was 99.3%, positive predictive value was 78.4%, negative predictive value was 99.8%, sensitivity was 93.6%, and specificity was 99.4%. A total of 29 (2.1%) cases of unilateral paralysis were observed, 23 (1.7%) of which were transient and 6 (0.4%) of which were permanent. Bilateral palsy was observed in two (0.1%) cases requiring a tracheostomy. In Group A, 31 (2.3%) injuries were observed, 25 (1.8%) of which were transient and 6 (0.4%) of which were permanent. In Group B, 26 (2.6%) unilateral paralysis cases were observed, 20 (2%) of which were transient and 6 (0.6%) of which were permanent; bilateral palsy was observed in 2 (0.2%) cases. In Group B, 28 (2.8%) injuries were observed, 21 (2.1%) of which were transient and 7 (0.7%) of which were permanent. Differences between the two groups were not statistically significant.

CONCLUSIONS

Our results show that IONM has a very high sensitivity and negative predictive value, but also good specificity and positive predictive value. For these reasons, in selected patients with LOS, the surgical strategy should be reconsidered. However, patients need to be informed preoperatively about potential strategy changes during the planned bilateral surgery. Future larger and multicenter studies are needed to confirm the benefits of this therapeutic strategy.

Medico legal aspects on neuromonitoring in thyroid surgery: informed consent on malpractice claims

AIM

The purpose of this paper is to provide a forensic profile framework of neuromonitoring in thyroid surgery, regarding the information given to the patient and its classification as part of professional liability in the event of recurrent injury.

METHOD

Evaluation and reflections on the required behaviour of the surgeon on providing details on the operation before the informed consent is given and to outline the possible legal implications regarding professional liability as a result of recurrent injury. In particular, if it is an obligation to inform the patient about using this method and if it is possible for the surgeon to freely choose whether to employ this method, which is still burdened by a certain percentage of error and for that reason it cannot be defined a "standard of care".

RESULTS

To recognize neuromonitoring the role of standard of care in surgery of the thyroid means attribute a role of method able to avoid the surgeon to cause iatrogenic damage to the laryngeal nerve. For the foregoing reasons that is not true, determining false positives and false negatives, and this can be a double edged sword for the surgeon.

CONCLUSIONS

Although the progress in the field of thyroid surgery made in the last decade, currently there is no scientific reassuring evidence to completely avoid the possibility of producing an iatrogenic lesion of the laryngeal nerve. Information given to the patient prior to surgery should respect the requirements of completeness, freedom and honesty in order to allow the patient to self-determination.

Intraoperative nerve monitoring during thyroid surgery

PURPOSE OF REVIEW

Laryngeal nerve injury, resulting in speech and swallowing dysfunction, is a feared complication of thyroid operations. Routine visualization of the recurrent laryngeal nerve (RLN) has decreased the likelihood of nerve injury, and intraoperative nerve monitoring has been applied in the hope of further enhancing safety.

RECENT FINDINGS

There is conflicting evidence about the value of nerve monitoring during thyroid operations, despite ample research. The data favor nerve monitoring in certain situations, such as neck re-explorations, contralateral RLN injury, extensive or challenging dissections, invasive tumors or large goiters, and nonrecurrent or branching recurrent laryngeal nerves. Continuous intraoperative nerve monitoring may reduce the chances of excessive traction, which is the most common mechanism of injury. Nerve monitoring may also identify and protect the external branches of the superior laryngeal nerve.

SUMMARY

Surgeons should routinely identify recurrent laryngeal nerves during thyroid operations, and intraoperative nerve monitoring might be a useful adjunct to prevent injury. As a result of the relatively low probability of permanent recurrent laryngeal nerve injury, it is difficult to establish the absolute value of nerve monitoring. Further research may focus on continuous nerve monitoring and intraoperative monitoring of the external branches of the superior laryngeal nerves.