Journal of Head and Neck Surgery

ISSN: 2689-8713

Research Article | VOLUME 3 | ISSUE 1 | DOI: 10.36959/605/554 OPEN ACCESS

Continuous Intraoperative Nerve Monitoring in Thyroidectomies: A Systematic Review and Meta-Analysis

Dominic Ku, Michelle Hui, Phylannie Cheung, Mark Smith, Faruque Riffat, Niranjan Sritharan, Dipti Kamani and Gregory Randolph

  • Dominic Ku 1*
  • Michelle Hui 1
  • Phylannie Cheung 1,2
  • Mark Smith 1,2
  • Faruque Riffat 1,2
  • Niranjan Sritharan 1,2
  • Dipti Kamani 3
  • Gregory Randolph 3,4
  • Department of Otolaryngology Head & Neck Surgery, Westmead Hospital, Sydney, Australia
  • Department of Otolaryngology Head & Neck Surgery, Nepean Hospital, Sydney, Australia
  • Department of Otolaryngology, Massachusetts Eye and Ear Infirmary, Boston, Massachusetts, USA
  • Division of Surgical Oncology, Department of Surgery, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts, USA

Ku D, Hui M, Cheung P, et al. (2021) Continuous Intraoperative Nerve Monitoring in Thyroidectomies: A Systematic Review and Meta-Analysis. J Head Neck Surg 3(1):122-132

Accepted: January 26, 2021 | Published Online: January 28, 2021

Continuous Intraoperative Nerve Monitoring in Thyroidectomies: A Systematic Review and Meta-Analysis

Abstract


Objective

Application of intermittent intra-operative nerve monitoring (I-IONM) as an aid in thyroidectomies is common practice worldwide. While I-IONM is significantly beneficial in thyroid surgeries, it is limited by its intermittent nature, thereby allowing the recurrent laryngeal (RLN) nerve to be at risk of injury in-between stimulations. In the last decade, the introduction of continuous intraoperative RLN monitoring (CIONM) has overcome this limitation by enabling 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 CIONM utility for thyroid surgery by conducting the first meta-analysis on this technique.

Methods

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 2019. Medical subject headings (MeSH) terms utilised 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.

Results

A total of 23 papers that utilised continuous vagal nerve monitoring during thyroid surgery were identified. The proportion of temporary and permanent recurrent laryngeal nerve paralysis post-operation was 2.5% (95% CI 1.7-3.2%, I2 = 37.7). The proportion of patients with permanent recurrent laryngeal nerve palsy post-operation was 0.05% (95% CI 0.08 - 0.2%, I2 = 0).

Conclusion

CIONM is a safe and effective means by which RLN paralyses in thyroid surgery can be reduced.

Keywords


Thyroidectomy, Surgery, Nerve monitoring, Vagal nerve, Recurrent laryngeal nerve, Nerve paralysis, Nerve palsy

Introduction


Continuous intraoperative nerve monitoring (CIONM) via continuous vagal nerve stimulation for thyroid and parathyroid surgeries is a technology widely available throughout the past decade. Nevertheless, it has yet to be adopted as a routinely utilised adjunct to the established technique of intermittent intraoperative recurrent laryngeal nerve monitoring and direct visualisation. Although demonstrated to be a safe and effective technique of nerve monitoring in multiple centres [1-11], this study aims to demonstrate the summative result of this data in a meta-analysis of CIONM-related recurrent laryngeal nerve outcomes in thyroid surgery.

Since the introduction of recurrent laryngeal nerve monitoring (RLN) in thyroid surgery as an adjunct to direct visualisation, permanent vocal cord paralysis (VCP) has been greatly reduced in uncomplicated primary surgery [12,13]. With the use of intermittent intraoperative nerve monitoring (I-IONM), rates of temporary VCP range between1 to 9% and rates of permanent VCP range between 0 to 3% [14]. However, in revision surgery or surgery in more complex cases such as thyroid cancer surgery and Graves' disease, the paralysis rates may be as high as 20% [15,16]. In cases where there is a loss of signal from the RLN on the first side of resection, a two-staged procedure has been strongly advocated to avoid the dire consequence of bilateral RLN paralysis [17,18]. This adverse outcome is estimated at 0.4%, and carries with it a potential risk of emergency airway surgery such as tracheostomy and intensive care admission [19].

The use of indirect RLN monitoring by vagal nerve stimulation ensued as authors realised the possibility of missing an injury distal to the point of direct RLN stimulation [20-22]. This principle was confirmed by Thomusch, et al. from prospectively collected data of more than 1500 nerves at risk, demonstrating the superior reliability of indirect IONM stimulation compared to direct RLN stimulation (p < 0.05, specificity of 97.6%, negative predictive value 99.6%) [23].

A methodical shortcoming has always existed for I-IONM in that the RLN remains at risk of damage between two manual stimulations. Efforts in developing continuous real-time nerve monitoring were first published by Lamade, et al. in 2007 [24]. The group first developed a double-balloon electromyography tube prototype and later a tripolar hybrid cuff electrode embedded in a silicone cuff which enabled continuous uninterrupted nerve monitoring by low current stimulation [25]. Later in 2009, Schneider, et al. developed a bipolar anchor electrode placed in contact with the vagal nerve between the common carotid artery and internal jugular vein [26]. Currently, one of the more popular systems utilised is the Automatic Periodic Stimulation (APS) electrodes (Medtronic, Minnesota, USA) which are placed on the vagal nerves, in conjunction with the Nerve Integrity Monitoring Electromyogram (NIM EMG) endotracheal tube (Medtronic).

These systems utilise electromyography (EMG) enabling real-time feedback of the entire Vagal-RLN axis. While I-IONM aids in identifying the RLNs, thereby reducing the chance of nerve transection, CIONM can detect early EMG changes that are associated with imminent nerve injuries, thus preventing nerve injuries caused by mechanical, thermal or cumulative trauma by forewarning the surgeons of impending nerve injury and allowing the surgeons to perform corrective manoeuvres [26].

Studies advocating for the use of CIONM point to the inherent disadvantage of I-IONM: Its inability to alert circuit discontinuity; effectively only able to prevent potential RLN injury until the nerve is stimulated after such injury has been caused. Authors championing the use of CIONM highlight the very point of injury prevention by early detection of nerve stress detected by electromyography [2]. CIONM equips the surgeon with knowledge of real-time functional status of RLN, thus allowing for immediate adjustment of surgical manoeuvres and pivotal intraoperative decision making such as a staged contra lateral thyroidectomy where the integrity of the RLN on the first side is uncertain [27]. With the availability of technology and data, the onus is on the surgeon to provide the best care available to minimise adverse events. In this study, we aim to report the rate of VCP in studies utilising CIONM for thyroid surgery. We hypothesise that the use of CIONM would lead to comparable or lower rates of RLN injury when compared to I-IONM alone.

Materials and Methods


Search strategy

This meta-analysis had the primary objective of evaluating the role of CIONM on rates of RLN injury in subjects undergoing thyroid surgery. Our secondary goal was assessing other adverse events associated with CIONM. Articles published in all languages were searched via The Cochrane Collaboration Library, Medline and EMBASE database from Jan 1946 to April 2020. The following search strategy was used: #1, thyroid gland or thyroidectomy; #2, recurrent laryngeal nerve; #3, vagus nerve or vagal; #4, monitor* or stimulat*, #2 or #3 (526032 articles) which is #5, #4 and #5 (59684 articles) which is #6, then #1 and #6 (475 articles). After duplicates were removed, there were 383 articles (Table 1). Another 5 articles were included in a hand search.

Study selection and data extraction

The abstracts were reviewed by two authors (DK and MH) independently with predefined inclusion and exclusion criteria according to the PRISMA guidelines (refer to PRISMA flowchart for reference, Figure 1). The selection of studies was guided by the PICOS principle as per PRISMA guidelines. Inclusion criteria were as follows, Patients: Undergone thyroid surgery, Intervention: CIONM, Comparisons: I-IONM or direct visualisation, Outcomes: Temporary and permanent VCP, Study design: Retrospective or prospective clinical trials. Exclusion criteria were as follows: Non-human studies, articles not reporting rates of temporary or permanent recurrent laryngeal paralysis rates, case series less than 5 patients. Uncertainties or conflicts were resolved by review of the full paper and discussion among the reviewers and other authors. Data was extracted from the articles and collected on a spreadsheet. Studies with reporting on the same population were identified, and results extracted once only so that they were not replicated.

Risk of bias assessment

The risk of bias for each eligible study was independently assessed by two review authors (DK and MH). Prospective cohort studies and retrospective cohort studies were assessed by the ACROBAT-NRSi Cochrane Risk of Bias Tool [28]. The seven domains including confounding, selection of participants, classification of interventions, deviations from intended intervention, missing data, measurement of outcomes and selection of reported results were assessed and categorised into low, moderate, severe, or unclear risk of bias. An overall assessment of risk of bias for each study was reported as low, moderate, serious, critical of no information on the risk of bias.

Primary and secondary outcomes

Our primary outcomes were defined a priori and included temporary and permanent vocal cord paralysis (VCP) rates, whilst our secondary outcomes were any monitoring related adverse events. Rates of VCP were calculated by recording number of paralysed nerves over total number of nerves at risk. Temporary VCP was differentiated from permanent VCP by the final follow-up status of vocal cords as observed by fiberoptic examination, which was at three months for the majority of published articles. Patient age, gender and proportion of cases with Graves' disease, thyroiditis and thyroid cancer were recorded if reported. Secondary outcomes reported were defined as side-effects of CIONM, such as mechanical nerve injury or autonomic disturbances such as bradycardia, arrhythmias and hemodynamic instability.

Statistical analysis

Meta-analysis was performedusing a random effect model and assessed with the I2 value with RStudio (version 1.3.1093) [29]. Rates of temporary and permanent VCP were aggregated with effect size calculated as a function of events (temporary or permanent VCP over the total number of nerves at risk. The calculation of the standard error, variance and 95% confidence intervals assume the effect size calculated follows a normal distribution, which is true for increasingly large sample sizes (based on the Central Limit Theorem). For smaller sample sizes, the distribution of the effect size may well be skewed, and hence the calculation of the confidence intervals may result in a negative value for the lower limit. Based on the formula of heterogeneity [16], I2 was used to quantify heterogeneity of rates of temporary and permanent VC paralysis in the studies. The interpretation of I2 < 0 is the same as that of I2 = 0. Negative values of I2 are rounded up to zero, and interpreted as no observed heterogeneity [30]. The heterogeneity was low among the studies, hence fixed effect model was employed.

Results


A total of 23 papers were included for the systematic review from the initial search result of 440 papers (see Figure 1 for PRISMA flowchart). These papers consisted of 7 retrospective cohort studies and 15 prospective cohort studies published and one prospective randomised controlled trial between the years 2007 and 2019 (Table 2).

Risk of bias assessment for included studies

The risk of bias assessment for all 23 studies is presented in Table 3. Most studies exhibited moderate risk of bias according to the seven categories of assessment. The most prevailing feature of bias appeared to be the high variability in operations, including benign, malignant and revision surgeries as well as lobotomy, hemithyroidectomy, total thyroidectomy and neck dissections. The variability in pathology and operation in the studies may increase the risk of bias in reporting the efficacy of CIONM in thyroid surgery. There is a significant risk of publication bias. This review of literature has only identified one article by Terris, et al. reporting a termination of a study due to the adverse events directly from CIONM [31].

Patient characteristics

A total of 3040 patients and 5007 nerves at risk were reported to have undergone continuous intraoperative vagal nerve monitoring in the context of thyroid surgery. We observed a female preponderance with 76.4% females in the patient population. The mean age of patients ranged from 38 to 61 years of ageing the adult population, and one paper reported on a paediatric population between 4 to 18 years of age [32] (Table 2).

A significant proportion of papers did not report important patient diagnosis for the CIONM groups i.e. Graves' disease, thyroiditis or thyroid cancer specifically, albeit having reported it for the overall study (Table 2). However, most papers note that patients at higher risk of nerve paralysis were generally selected for CIONM. There were various definitions of high risk procedures; Yu, et al. denoted six patient groups: 1) Revision surgery, 2) Pre-existing unilateral VCP undergoing bilateral thyroidectomy or contralateral thyroidectomy, 3) Involves retrosternal goitre, 4) Suspected bilateral multiple carcinomas, 5) Suspected large carcinomas with dorsal extension invading into surrounding tissue and 6) Graves' disease patients [10].

Vagal nerve stimulation apparatus

The papers from our systematic review spanned over two decades, reflecting the evolution of direct vagal nerve stimulation apparatus. Although most centres utilised a handheld bipolar stimulation probe for intermittent direct stimulation of the vagal nerve (VN) and RLN, a number of different designs were tried out for CIONM of the VN. The pioneering studies by Lamade and Ulmer, et al. [30,31] in conjunction with the Fraunhofer Institute and Inomed constructed a tripolar silicone cuffed electrode that enveloped the VN longitudinally [25,33]. This group, in association with the IKONA consortium, later developed a saxophone-shaped back strap tripolar stimulation electrode [34-36].

In 2007, Schneider, et al. introduced another vagal nerve stimulator developed in cooperation with Bioprocessing and Analytical Measurement Techniques (Heiligenstadt, Germany) and Dr. Langer Medical Gmb H. This was a t-shaped electrode that anchored between the carotid vessels and the vagal nerve after dissecting the carotid sheath for about 2 cm.

Since then, the majority of the remaining papers (12 of 15) reported the use of the Automatic Periodic Stimulation (APS) VN stimulator (2.0 or 3.0 mm, Medtronic, Jacksonville, FL, USA). Although first reported by Vlastarakos and Mochloulis, et al. in 2011 [37], it was Schneider and Randolph, et al. who published the first cohort study with the use of this device. The APS system generates a continuous electrical pulse during the operation (10 per min, 100 µs, 1 mA) [38].

Vocal cord paralysis rates

This meta-analysis focuses on temporary and permanent vocal cord paralysis rates in the reviewed papers, the combined events are displayed in a forest plot (Figure 2). The accumulative data from papers published between 2007 and 2019 were analysed using a random effect model. The proportion of patients with temporary and permanent VCP were 2.5% (95% CI 1.7-3.2%, I2 = 37.7) (Table 4). The proportion of patients with permanent VCP was 0.05% (95% CI 0.08-0.2%, I2 = 0) (Table 5).

The papers which utilised the APS (Medtronic) VN stimulator were further analysed separately. The proportion of patients with temporary and permanent VCP were 0.59% (95% CI 0.23-0.94%, I2 = 0) (Table 6). The proportion of patients with permanent VCP was 0.08% (95% CI 0-0.32%, I2 = 38.9) (Table 7).

There was one paper which reported two cases of bilateral VCP requiring emergency tracheostomy and tracheostomy tube for 15 days. Both patients had recovery of their VC function in the next 3 months. Both cases had intact neuromonitoring tracings and the paralyses were attributed to incorrect placement of tracheal tube inflatable cuffs over the vocal cords [39].

Safety of VN stimulation during CIONM

The majority of the papers in this review have reported safe use of VN stimulation without autonomic disturbances when stimulation currents and frequencies were kept low [10,40-42]. The safety of CIONM was also established in paediatric populations [32] and high-risk populations such as those with advanced atrioventribular blocks [2]. However, there were instances of adverse effects reported in a minority of cases. Terris, et al. reported two cases of complications directly related to the application of VN monitoring in a series that was abruptly ceased due to the perceived increased risk of CIONM. This paper reported 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. Subsequently, Brauckhoff, et al. also reported electrode related VN injury resulting in temporary VN paralysis in a minority of patients (2 nerves, 2% nerves at risk) [43]. Marin Arteaga, et al. reported similar rates of temporary VN paralysis (3 nerves, 1.9% nerve at risk). The authors postulated this could be caused by traction when exposing the nerve or perineural bleeding, but no haematoma was visualised [8].

Discussion


This meta-analysis found no permanent vagal nerve palsy and only 6 cases of temporary vagal nerve palsy of a total of 5007 nerves at risk resulting from the use of CIONM. There was one reported case of haemodynamic instability by Terris, et al. resulting the use of VN monitoring [31]. The overall rate of VCP was 2.5% and a permanent rate of VCP was 0.05%. These aggregated results indicate lower VCP rates when compared to published data on I-IONM or visualisation alone.

Since the introduction of IONM to thyroid surgery, its benefits in expediting RLN identification, reducing RLN paralysis and avoidance of bilateral VCP has been realised [44]. The use of IONM via electromyography has been recommended as an option by the American Academy of Otolaryngology Clinical Practice guidelines since 2013 [45]. Furthermore, since 2011 the German Association of Endocrine Surgeons has recommended the use of IONM for all thyroid surgery, citing its additional utility in revision surgery and postoperative prognostication of neural function [46]. Furthermore, the use of IONM has equipped the surgical operator with knowledge of RLN function at key intraoperative decision points. The awareness of a loss of signal (LOS) on the initial side of thyroidectomy allows the surgical operator to delay contralateral thyroidectomy in a staged procedure, thereby reducing the dreaded complication of bilateral VC paralysis to near zero [18,47,48]. With proven utility, IONM has taken up an important role in optimising the safety of thyroidectomy surgery.

Since the introduction of IONM to thyroid surgery, its benefits in expediting RLN identification, reducing RLN paralysis and avoidance of bilateral VCP has been realised [44]. The use of IONM via electromyography has been recommended as an option by the American Academy of Otolaryngology Clinical Practice guidelines since 2013 [45]. Furthermore, since 2011 the German Association of Endocrine Surgeons has recommended the use of IONM for all thyroid surgery, citing its additional utility in revision surgery and postoperative prognostication of neural function [46]. Furthermore, the use of IONM has equipped the surgical operator with knowledge of RLN function at key intraoperative decision points. The awareness of a loss of signal (LOS) on the initial side of thyroidectomy allows the surgical operator to delay contralateral thyroidectomy in a staged procedure, thereby reducing the dreaded complication of bilateral VC paralysis to near zero [18,47,48]. With proven utility, IONM has taken up an important role in optimising the safety of thyroidectomy surgery.

There have been historic concerns regarding the safety of CIONM [31,43]. However multiple large cohort studies including one study with advanced atrioventricular block demonstrated no adverse systemic effects of VN stimulation at the operational 1 to 2 mA current [2]. The operational currents for CIONM are only supramaximal for the efferent motor A fibres and myelinated autonomic B fibres, therefore do not activate demyelinated C fibres responsible for autonomic response [26]. This is based on previous studies which demonstrated cardiopulmonary response from activation of C fibres within the VN was only elicited with 2 mA or greater strength [51]. Furthermore, stimulation frequencies were kept below 30 Hz (not more than 3 Hz for CIONM in thyroid surgery) and applied at pulsatile intervals less than 100 ms duration; these parameters have not be associated with adverse events to date [1,52].

The successful application of CIONM is contingent on surgical expertise, equipment calibration, recognition of impending nerve injury and corresponding manoeuvres to alleviate potential damage to the RLN. Regardless of the manufacturers, the CIONM apparatus generally includes a multichannel EMG system, sensing endotracheal surface electrode, handheld stimulation electrode and direct VN electrode. In order to utilise CIONM proficiently, the surgeon must overcome the learning curve involved in both the technical application of CIONM apparatus and interpretation of EMGs. The detailed surgical techniques and calibration of various CIONM systems are described in other studies and are beyond the scope of this paper [1,52].

The fundamental advancement in CIONM is its ability to detect potential insult to the RLN, thereby allowing the surgeon to respond to this threat immediately, avoiding damage to the RLN [40]. This is expressed in EMG changes during CIONM. The surgeon must develop expertise in interpreting real-time EMG changes and act accordingly. Schneider, et al. have aptly summarised EMG changes and corresponding risk classification of potential RLN injury based on multiple large cohort trials and animal studies [40,42,50,52]. Impending nerve injury can be detected by EMG combined events (CE), which were defined as greater than 50% decrease in amplitude and concomitant greater than 10% increase in latency from baseline. Such insults have been shown to be caused mainly by traction and the reversal of related surgical manoeuvres have been shown to restore amplitude thus avoiding RLN injury in majority of cases (up to 80%) [14,38]. The ability to foresee potential injury and respond appropriately may explain the low rates of temporary and permanent paralyses observed in our meta-analysis when compared to conventional IONM alone (0.59% in the APS group compared to literature report of 2% in IONM [13].

Loss of signal (LOS) is more foreboding EMG changes. This was defined as a decrease of nerve amplitude to less than 100 microvolts (µV). This was further classified into segmental type 1 LOS and global type 2 LOS. Segmental type 1 LOS typically presents with a sudden loss of nerve amplitude and unchanged nerve latency, which is likely due to sudden stretching, haemostatic instruments used in proximity, pinching or transection of the nerve. Global type 2 LOS typically presents with a fluctuating loss of nerve amplitude, which is likely due to traction stress on the nerve and the damage is often reversible upon release of the nerve [42]. Good prognosticating factors for nerve recovery after LOS include slow onset of LOS, and the presence of and degree of intra-operative amplitude recovery [52].

During the operation, if there was a LOS and failure to regain 50% of baseline amplitude, there is a significant risk of early postoperative VCP (43). CIONM has a predictive accuracy of 99.5% and lower false positive and negative rates than IONM (0.3% vs. 0.5% and 0.2% vs. 0.6% respectively) [52]. Endowed with the dependable information CIONM provides, the surgical team is in optimal position for intraoperative decision making. We believe it is precisely due to the ability to continually confirm RLN status, and reliably predict postoperative RLN function that this meta-analysis has reported record low rates of temporary, permanent and bilateral vocal cord paralysis.

Limitations


This study aims to report on the current evidence for the use of CIONM in thyroid surgery. The data currently available in the literature is limited due to study design - there was only one randomised control trial for CIONM at present. There is a need to standardise data reporting in regard to patient demographics, pre- and intraoperative risk factors, intra-operative nerve monitoring and post-operative follow-up. Finally, this study reported from a relatively narrow range of institutions with several centres publishing multiple studies - it is difficult to separate the benefit tertiary centres and expert surgeons from the true effect of CIONM in thyroid surgery.

Conclusion


Continuous intraoperative vagal nerve monitoring has been shown to be a reliable and safe mechanism by which recurrent laryngeal nerve injury can be prevented, and thus, offer the best chance of optimal vocal cord function after thyroid surgery. With definitive data at hand, the surgical operator should consider the use of CIONM especially in high risk thyroidectomy procedures.

Acknowledgements


Statistical analysis was assisted by Mr Vikas K Sewani (B. Sci (Maths) BEng, PhD candidate at Centre for Quantum Computation and Communication Technology, Sydney Australia).

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  45. Chandrasekhar SS, Randolph GW, Seidman MD, et al. (2013) Clinical practice guideline: Improving voice outcomes after thyroid surgery. Otolaryngol Head Neck Surg148: S1-S37.
  46. Musholt TJ, Clerici T, Dralle H, et al. (2011) German association of endocrine surgeons practice guidelines for the surgical treatment of benign thyroid disease. Langenbeck's Arch Surg 396: 639-649.
  47. Dionigi G, Frattini F (2013) Staged thyroidectomy: Time to consider intraoperative neuromonitoring as standard of care. Thyroid 23: 906-908.
  48. Melin M, Schwarz K, Lammers BJ, et al. (2013) IONM-guided goiter surgery leading to two-stage thyroidectomy-indication and results. Langenbeck's Arch Surg 398: 411-418.
  49. Hermann M, Hellebart C, Freissmuth M (2004) Neuromonitoring in thyroid surgery: Prospective evaluation of intraoperative electrophysiological responses for the prediction of recurrent laryngeal nerve injury. Ann Surg 240: 9.
  50. Kandil E, Mohsin K, Murcy MA, et al. (2018) Continuous vagal monitoring value in prevention of vocal cord paralysis following thyroid surgery. Laryngoscope 128: 2429-2432.
  51. Groves DA, Brown VJ (2005) Vagal nerve stimulation: A review of its applications and potential mechanisms that mediate its clinical effects. Neurosci Biobehav Rev 29: 493-500.
  52. Schneider R, Randolph GW, Barczynski M, et al. (2016) Continuous intraoperative neural monitoring of the recurrent nerves in thyroid surgery: A quantum leap in technology. Gland surgery 5: 607-616.

Abstract


Objective

Application of intermittent intra-operative nerve monitoring (I-IONM) as an aid in thyroidectomies is common practice worldwide. While I-IONM is significantly beneficial in thyroid surgeries, it is limited by its intermittent nature, thereby allowing the recurrent laryngeal (RLN) nerve to be at risk of injury in-between stimulations. In the last decade, the introduction of continuous intraoperative RLN monitoring (CIONM) has overcome this limitation by enabling 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 CIONM utility for thyroid surgery by conducting the first meta-analysis on this technique.

Methods

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 2019. Medical subject headings (MeSH) terms utilised 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.

Results

A total of 23 papers that utilised continuous vagal nerve monitoring during thyroid surgery were identified. The proportion of temporary and permanent recurrent laryngeal nerve paralysis post-operation was 2.5% (95% CI 1.7-3.2%, I2 = 37.7). The proportion of patients with permanent recurrent laryngeal nerve palsy post-operation was 0.05% (95% CI 0.08 - 0.2%, I2 = 0).

Conclusion

CIONM is a safe and effective means by which RLN paralyses in thyroid surgery can be reduced.

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