Recurrent laryngeal nerve safety parameters of the Harmonic Focus during thyroid surgery: Porcine model using continuous monitoring

Improving Voice Outcomes after Thyroid Surgery and Ultrasound-Guided Ablation Procedures

The field of endocrine surgery has expanded from the traditional open neck approach to include remote access techniques as well as minimally invasive approaches for benign and malignant thyroid nodules. In experienced hands and with careful patient selection, each approach is considered safe, however complications can and do exist. Post-operative dysphonia can have serious consequences to the patient by affecting quality of life and ability to function at work and in daily life. Given the significance of post-procedural dysphonia, we review the surgical and non-surgical techniques for minimizing and treating recurrent laryngeal nerve injury that can be utilized with the traditional open neck approach, remote access thyroidectomy, or minimally invasive thermal ablation.

Effects of Intraoperative Neural Tunnel in Protecting Recurrent Laryngeal Nerve: Experiences in Open, Trans Breast, and Transoral Endoscopic Thyroidectomy

Background

Energy-based devices (EBDs) increase the risks of thermal nerve injuries. This study aimed to introduce a surgical strategy of intraoperative neural tunnel protecting (INTP) for evaluating the effect in reducing the incidence of recurrent laryngeal nerve (RLN) damage in open, trans breast, and transoral endoscopic thyroidectomy.

Methods

INTP strategy was introduced: a tunnel was established and protected by endoscopic gauze along the direction of the nerve. A total of 165, 94, and 200 patients with papillary thyroid carcinoma (PTC) were to use INTP in respectively open, trans breast, and transoral endoscopic thyroidectomy as the INTP group. Additionally, 150, 95, and 225 patients who received the same methods without INTP were enrolled in the control group. Ipsilateral thyroidectomy or total thyroidectomy, and central compartment dissection were performed on the enrolled patients.

Results

Clinicopathologic characteristics, surgical outcomes, and surgical complications were similar between the INTP group and the control group in open, trans breast, and transoral endoscopic thyroidectomy. The incidences of electromyography (EMG) changes in the INTP group were lower as compared to the control group in trans breast endoscopic thyroidectomy (p < 0.05). The incidence of postoperative hoarse in the INTP group was lower as compared to the control group in open and transoral endoscopic thyroidectomy (p < 0.05). Postoperative calcium levels (p < 0.01) were significantly higher, and the white blood cells (p < 0.05) and C-reactive protein levels (p < 0.01) were significantly decreased in the INTP group compared with the control group in transoral endoscopic thyroidectomy.

Conclusions

This was the first instance of the INTP strategy being introduced and was found to be an effective method for protecting the RLN in open, trans breast, and transoral endoscopic thyroidectomy. Additionally, INTP helped protect other important tissues such as the parathyroid glands in transoral endoscopic thyroidectomy as well as in reducing postoperative inflammatory responses.

Safety Parameters of Quantum Molecular Resonance Devices During Thyroid Surgery: Porcine Model Using Continuous Neuromonitoring

OBJECTIVES

Quantum molecular resonance (QMR) devices have been applied as energy-based devices in many head and neck surgeries; however, research on their use in thyroid surgery is lacking. This study aimed to investigate the safety parameters of QMR devices during thyroidectomy when dissection was adjacent to the recurrent laryngeal nerve (RLN).

METHODS

This study included eight piglets with 16 RLNs, and real-time electromyography (EMG) signals were obtained from continuous intraoperative neuromonitoring (C-IONM). QMR bipolar scissor (BS) and monopolar unit (MU) were tested for safety parameters. In the activation study, QMR devices were activated at varying distances from the RLN. In the cooling study, QMR devices were cooled for varying time intervals, with or without muscle touch maneuver (MTM) before contacting with the RLN.

RESULTS

In the activation study, no adverse EMG change occurred when QMR BS and MU were activated at distances of 2 mm or longer from the RLNs. In the cooling study, no adverse EMG change occurred when QMR BS and MU were cooled in 2-second intervals or immediately after MTM.

CONCLUSION

QMR devices should be carefully used when performing RLN dissection during thyroid surgery. According to the activation and cooling safety parameters in this study, surgeons can avoid RLN injury by following standard procedures when using QMR devices.

Necessity of Routinely Testing the Proximal and Distal Ends of Exposed Recurrent Laryngeal Nerve During Monitored Thyroidectomy

OBJECTIVES

Intraoperative neuromonitoring (IONM) is a useful tool to evaluate the function of recurrent laryngeal nerve (RLN) in thyroid surgery. This study aimed to determine the necessity and value of routinely testing the proximal and distal ends of RLN.

METHODS

In total, 796 patients undergoing monitored thyroidectomies with standardized procedures were enrolled. All 1346 RLNs with visual integrity of anatomical continuity were routinely stimulated at the most proximal (R2p signal) and distal (R2d signal) ends after complete RLN dissection. The EMG amplitudes between R2p and R2d signals were compared. If the amplitude of R2p/R2d ratio reduction (RPDR) was over 10% or loss of signal (LOS) occurred, the exposed RLN was mapped to identify the injured point. Pre- and post-operative vocal cord (VC) mobility was routinely examined with video-laryngofiberscope.

RESULTS

Nerve injuries were detected in 108 (8%) RLNs, including 94 nerves with incomplete LOS (RPDR between 13%-93%) and 14 nerves with complete LOS. The nerve injuries were caused by traction in 80 nerves, dissecting trauma in 23 nerves and lateral heat spread of energy-based devices in 5 nerves. Symmetric VC mobility was found in 72 nerves with RPDR ≤50%. The occurrence of abnormal VC mobility (weak or fixed) was 14%, 67%, 100%, and 100% among the different RPDR stratifications of 51%-60%, 61%-70%, 71%-80%, and 81-93%, respectively. Of the 14 nerves with complete LOS, all showed fixed VC mobility. Permanent VC palsy occurred in 2 nerves with thermal injury.

CONCLUSION

Routinely testing the proximal and distal ends of exposed RLN helps detect unrecognized partial nerve injury, elucidate the injury mechanism and determine injury severity. The procedure provides accurate information for evaluating RLN function after nerve dissection and should be included in the standard IONM procedure.

Improving Voice Outcomes After Thyroid Surgery - Review of Safety Parameters for Using Energy-Based Devices Near the Recurrent Laryngeal Nerve

Technological advances in thyroid surgery have rapidly increased in recent decades. Specifically, recently developed energy-based devices (EBDs) enable simultaneous dissection and sealing tissue. EBDs have many advantages in thyroid surgery, such as reduced blood loss, lower rate of post-operative hypocalcemia, and shorter operation time. However, the rate of recurrent laryngeal nerve (RLN) injury during EBD use has shown statistically inconsistent. EBDs generate high temperature that can cause iatrogenic thermal injury to the RLN by direct or indirect thermal spread. This article reviews relevant medical literatures of conventional electrocauteries and different mechanisms of current EBDs, and compares two safety parameters: safe distance and cooling time. In general, conventional electrocautery generates higher temperature and wider thermal spread range, but when applying EBDs near the RLN adequate activation distance and cooling time are still required to avoid inadvertent thermal injury. To improve voice outcomes in the quality-of-life era, surgeons should observe safety parameters and follow the standard procedures when using EBDs near the RLN in thyroid surgery.

Heat production during pulmonary artery sealing with energy vessel-sealing devices in a swine model

OBJECTIVES

Energy vessel-sealing devices are being increasingly utilized to seal pulmonary artery (PA) branches during lobectomy. Heat from these devices can potentially injure surrounding tissues. We evaluated heat production from devices in a live animal model.

METHODS

PA branches were sealed in pigs with 4 energy vessel-sealing devices: 2 ultrasonic (US), 1 advanced bipolar or 1 mixed US and bipolar (mixed) device. Thermocouples were implanted in tissue surrounding the PA branch being sealed to measure tissue temperature. A thermal camera measured the sealing site and the temperatures of the instruments. Pathological analysis was performed on PA stumps to identify thermal damage.

RESULTS

A total of 37 PA branches were sealed in 4 pigs. Maximum tissue heat measured by the thermocouples for the 2 US, advanced bipolar and mixed devices was 42, 39, 42 and 46°C, respectively. The mean tissue temperatures at the site of the sealing measured with the thermal camera were 78, 75, 70 and 82°C (P = 0.834) and the mean instrument blade temperatures were 224, 195, 83 and 170°C (P = 0.000005) for the 2 US, advanced bipolar and mixed devices, respectively. The mean diameter of the region with tissue reaching 60°C or more measured with the thermal camera was between 4 and 6 mm for the 4 devices (P = 0.941). On pathological analysis, PA stumps had either thermal damage on the adventitia and external media (26/37) or transmural damage (11/37) at 1 mm from sealed site.

CONCLUSIONS

A 3-mm safety margin between the instrument blades and vital structures is recommended. Instrument blades can reach high temperatures that may cause tissue damage.

The area under the waveform of electromyography for monitoring the external branches of the superior laryngeal nerve during thyroid surgery

Background

Injuries to the external branches of the superior laryngeal nerve (EBSLN) are difficult to identify during thyroidectomy. Monitoring the low amplitudes of the EBSLN during surgery has proven to be complicated. Therefore a new parameter, the area under the waveform (AUW), was designed to improve monitoring efficiency. The aim of this study was to determine the effectiveness of using AUW to monitor the EBSLN during thyroidectomy.

Methods

A total of 927 patients and 927 recurrent laryngeal nerves (RLN) and EBSLNs who underwent monitored unilateral thyroidectomy were included. Standardized intraoperative neuromonitoring procedures were followed. RLN injuries were confirmed using stroboscopic laryngoscopy after surgery. EBSLN injuries were identified by means of observing changes in cricothyroid muscle (CTM) twitches when stimulated. Amplitude and AUW changes were assessed using statistical analysis. The correlations between AUW and amplitude were verified using the ratio of the two parameters to determine any decreases that were observed in the number of nerve injury cases. The receiver operating characteristic (ROC) curve was used to estimate the prediction of nerve injury.

Results

The overall injury rates of the RLN and EBSLN were 3.56% and 2.05%, respectively. The AUW for the RLN and EBSLN presented linear correlations with amplitude. In the RLN injury cases, no significant difference was observed between the two parameters (P>0.05). In the cases with EBSLN injuries, the AUW decreased 64.5%±14.1%, on average, which was a greater decrease compared to that observed for amplitude 49.7%±22.2% (P<0.0001). The summary of the EBSLN injury prediction included, amplitude vs. AUW, AUC: 0.918 vs. 0.994; P<0.0001, and Youden's index: 31.54% vs. 49.58%.

Conclusions

The AUW demonstrated consistency with the change in amplitude, and the observed changes were significant. The use of the AUW allowed successful predictions for both RLN and EBSLN nerve injuries. Also, the sensitivity of AUW was greater than amplitude for predicting EBSLN injuries.

Training Courses in Laryngeal Nerve Monitoring in Thyroid and Parathyroid Surgery- The INMSG Consensus Statement

Intraoperative neural monitoring (IONM) is now an integral aspect of thyroid surgery in many centers. Interest in IONM and the number of institutions that perform monitored thyroidectomies have increased throughout the world in recent years. For surgeons considering the introduction of IONM in their practice, specific training in IONM devices and procedures can substantially shorten the learning curve. The International Neural Monitoring Study Group (INMSG) has been at the forefront of IONM technology and procedural adoption since the introduction of neural monitoring in thyroid and parathyroid surgery. The purpose of this document is to define the INMSG consensus on essential elements of IONM training courses. Specifically, this document describes the minimum training required for teaching practical application of IONM and consensus views on key issues that must be addressed for the safe and reliable introduction of IONM in surgical practice. The intent of this publication is to provide societies, course directors, teaching institutions, and national organizations with a practical reference for developing IONM training programs. With these guidelines, IONM will be implemented optimally, to the ultimate benefit of the thyroid and parathyroid surgical patients.

Shaw scalpel use for recurrent laryngeal nerve dissection: safety parameter findings from continuous intraoperative neuromonitoring in swine models

Background

Precise dissection with hemostasis while preserving important structures is critical in thyroid surgeries. In this study, we tested the safety of the Hemostatix Shaw scalpel (HSS) around the recurrent laryngeal nerve (RLN) in porcine models.

Methods

Four piglets were used to obtain continuous intraoperative neuromonitoring data. The HSS was applied at various distances from the RLN, with various temperature settings. Monopolar electrosurgical pencil and Harmonic scalpel were also tested for comparison.

Results

The use of HSS did not show adverse electromyographic (EMG) events when activated at 3- and 5-mm distances from the RLN. At a 1-mm distance, adverse event was observed at 300 °C after 2 seconds of activation. At 210 °C, adverse event was observed when the instrument was directly adjacent to the RLN. For comparison, an electrosurgical pencil, set at coagulation mode (25W), showed an irreversible adverse EMG event during 5 seconds of activation at 1-mm distance from the RLN. Harmonic ACE+, activation power at level 5, was also applied in one RLN and reversable adverse EMG event was observed at <0.1-mm (contact) distance after 3 seconds of activation.

Conclusions

The safety distance of the HSS was 3 mm for the 300 °C setting and >1 mm for the 210 °C setting in the swine models in this study. Surgeons must understand the specific characteristics of various energy devices and apply them appropriately for safe operation.

Full percutaneous intraoperative neuromonitoring technique in remote thyroid surgery: Porcine model feasibility study

BACKGROUND

In remote thyroid surgery, a reliable intraoperative neuromonitoring (IONM) procedure is an important tool for reducing injury to recurrent laryngeal nerve (RLN). This study proposes an alternative or adjunct technique for performing full percutaneous (PC) IONM and confirms its feasibility in animal experiments.

METHODS

This prospective porcine model study enrolled four piglets with eight nerve sides. Evoked electromyography (EMG) was stimulated from PC ball-tip probe, and recorded from EMG endotracheal tube (ETT) and from PC paired long-needle electrodes on the perichondrium of the lateral aspect of thyroid cartilage.

RESULTS

In all RLNs and vagus nerves, typical laryngeal EMG waveforms were successfully evoked by PC probe stimulation and recorded by both ETT and PC needle electrodes.

CONCLUSIONS

This study confirms the feasibility of the full PC IONM techniques in porcine model. However, further clinical studies are needed to compare the practicality of different remote-access approaches for thyroid surgery.

Mechanisms of recurrent laryngeal nerve injury near the nerve entry point during thyroid surgery: A retrospective cohort study

BACKGROUND

The use of intraoperative neuromonitoring (IONM) for visual identification of recurrent laryngeal nerve (RLN) has decreased the rates of RLN injury (RLNI) during thyroid surgery. However, little attention has been paid to RLNI near the nerve entry point (NEP), where most injuries occur. The aim of this study was to determine the mechanism of RLNI near the NEP and to describe the recovery of nerve function.

METHODS

Patients undergoing thyroid surgery were analyzed to identify true loss of signal (LOS) by IONM. Follow-up for vocal cord palsy (VCP) was confirmed by a postoperative laryngoscopy. The risk factors for RLNI, the type of RLNI, the prevalence of VCP and the time for VCP recovery were all recorded and analyzed.

RESULTS

We analyzed 3582 at-risk nerves in 2257 surgical patients. The overall rate of RLNI near the NEP in at-risk nerves was 3.2%. RLNI was more likely to occur in nerves with extralaryngeal bifurcation (p = 0.013). The distribution of RLNI types, in order of frequency, was traction (52.6%; n = 61), compression (38.8%; n = 45), thermal (7.8%; n = 9), and nerve transection (0.9%; n = 1). Complete recovery from VCP was documented in 93.1% (n = 108) of RLNI.

CONCLUSION

Patients with a bifurcated RLN were at a higher risk of RLNI near the NEP than those without bifurcation. Traction and compression injuries occurred most frequently, but would eventually recover. Excessive stretching of the thyroid lobe played a role in RLNIs near the NEP.

Safety parameters of ferromagnetic device during thyroid surgery: Porcine model using continuous neuromonitoring

BACKGROUND

The ferromagnetic (FM) device is a new surgical energy modality. This study investigated dynamic recurrent laryngeal nerve (RLN) electromyographic (EMG) data to define safety parameters for using FM devices in thyroidectomy.

METHODS

Real-time EMG tracings obtained under continuous neuromonitoring were recorded from 24 RLNs (12 piglets). In the activation study, FM devices were activated at varying distances from the RLN. In the cooling study, FM devices were cooled for varying time intervals, or muscle touch maneuver was performed, before contact with the RLN.

RESULTS

During the FMwand/FMsealer activation, no adverse EMG events occurred at distances of 2 mm or longer. The cooling study revealed no adverse EMG events after 1-second (FMwand) or 3-second (FMsealer) intervals or after muscle touch maneuver.

CONCLUSIONS

An FM device should be activated at a distance of 2 mm from the RLN and should be adequately cooled before further contact with the RLN. Surgeons can avoid RLN injury by observing standard procedures for using FM devices.

Safety of Ligasure exact dissector in thyroidectomy with continuous neuromonitoring: a porcine model

Background

The purpose of this study was to investigate and define safety parameters for using the Ligasure exact dissector (LED) for dissection close to the recurrent laryngeal nerve (RLN) during thyroidectomy.

Methods

Real-time electrophysiologic electromyographic (EMG) tracings were recorded in 16 RLNs (8 piglets) during various applications of LED under continuous intraoperative monitoring in this prospective porcine model study. In the activation study, LED was activated at varying distances from the RLN. In the cooling study, LED was activated with different cooling times or after touching the sternocleidomastoid muscle before application to the RLN.

Results

In the activation study, no adverse EMG events occurred at distances longer than 1 mm. In the cooling study, no adverse EMG events occurred after a 2-second cooling time. Additionally, no adverse EMG events occurred when a sternocleidomastoid muscle touch maneuver was used for cooling.

Conclusions

The LED can be safely used at distance of 1 mm or longer, and it should be cooled for at least 2 seconds or by muscle touch maneuver. Thyroid surgeons can avoid RLN injury if standard procedures for LED use are observed.

Feasibility of Attachable Ring Stimulator for Intraoperative Neuromonitoring during Thyroid Surgery

OBJECTIVE

Stimulator-attached dissecting instruments are useful for intraoperative nerve monitoring during thyroidectomy. The aim of this study was to evaluate the feasibility of an attachable ring stimulator (ARS) by comparing the electromyography (EMG) amplitudes evoked by an ARS and a conventional stimulator.

METHODS

Medical records of fourteen patients who underwent thyroidectomy using intraoperative neuromonitoring between June and August 2019 were retrospectively reviewed. The amplitudes of V1, R1, R2, and V2 signals were checked using both the ARS and a conventional stimulator, at the same point.

RESULTS

Both stimulators were tested on 20 recurrent laryngeal nerves (RLNs) and 20 vagus nerves (VNs). In all the nerves, the amplitudes of V1, R1, R2, and V2 were greater than 500 μV. The mean amplitudes of V1, R1, R2, and V2 checked with the ARS were 1175, 1432, 1598, and 1279 μV, respectively. The mean amplitudes of V1, R1, R2, and V2 checked with the conventional stimulator were 1140, 1425, 1557, and 1217 μV, respectively. Difference between amplitudes evoked by the two stimulators for V1, R1, R2, and V2 was 77, 110, 102, and 99 μV, respectively. There was no statistical difference in the amplitudes between the two groups for V1, R1, R2, and V2.

CONCLUSION

The ARS transferred electric stimulation as effectively as the conventional stimulator. It is an effective tool for repeated stimulation and facilitates continuous feedback regarding the functional integrity of nerves during thyroid surgery.

Lateral thermal spread induced by energy devices: a porcine model to evaluate the influence on the recurrent laryngeal nerve

BACKGROUND

Recurrent laryngeal nerve (RLN) paralysis is a frequently observed complication after esophagectomy, and thermal injury is considered to be one of the causes. The difference in the lateral thermal spread associated with the grasping range of various energy devices remains unknown.

METHODS

Ultrasonic devices (Harmonic® HD1000i and Sonicision™) and a vessel-sealing device (Ligasure™) were studied. We evaluated the temperature of these devices, the activation time required, and the thermal spread on porcine muscle when the devices were used with different grasping ranges (thermal spread study). In addition, we evaluated the influence of thermal spread by short grasping use of the energy devices on the viability of RLN in a live porcine model (NIM study).

RESULTS

In the thermal spread study, the temperature of the ultrasonic devices lowered as grasping range increased, whereas the highest temperature of Ligasure was observed when used with two-thirds grasping. The activation time of ultrasonic devices became longer as grasping range increased, whereas the grasping range did not influence the activation time of Ligasure. Thermal spreads 1 mm from the energy devices were unaffected by the grasping ranges. Although the temperature of the Ligasure was lower than that of the ultrasonic devices, thermal spread by Ligasure was significantly greater than that induced by the ultrasonic devices. In the NIM study, the activation of the Sonicision with one-third grasping range did not cause EMG changes at distances of up to 1 mm from the RLN, whereas applying Ligasure with a one-third grasping range 1 mm away from the RLN led to a critical result.

CONCLUSIONS

The grasping range did not influence the thermal spread induced by the energy devices. Ultrasonic devices may be safer in terms of lateral thermal spread to the RLN than Ligasure.

Assessment of the Safety of the New Hybrid Pencil Type Energy (NP) Device Used Close to the Recurrent Laryngeal Nerve in a Porcine Model: Comparison With a Conventional Electrosurgical Knife

BACKGROUND

Recurrent laryngeal nerve (RLN) paralysis is mainly associated with esophagectomy, and it may result in not only other morbidities, such as aspiration pneumonia, but also in long-term issues. Therefore, an approach to prevent RLN paralysis is necessary. The present study was designed to determine the technical usability of the new hybrid pencil type energy (NP) device developed by Olympus Corporation (Tokyo, Japan) and compare it with a conventional electrosurgical knife (EK) for resection around the RLN lymph nodes.

METHODS

This nonsurvival (acute) study included 10 pigs (20 RLNs) and investigated the threshold for thermal RLN damage with the NP device and a conventional EK. To obtain basic information for our study, a preliminary experiment for heat spread was performed.

RESULTS

When using the EK device, the amplitude value disappeared at a distance of 1 mm from the RLN, but when using the NP device, the amplitude value was maintained up to a distance of 0.5 mm. There were significant differences at distances of 0 mm, 0.5 mm, and 1 mm between the NP and EK devices. Furthermore, heat spread was lower with the NP device than with the EK device.

CONCLUSIONS

The new energy device developed by Olympus Corporation was found to be technically safe for resection of the RLN lymph nodes in a porcine model. To the best of our knowledge, this is the first study to demonstrate the potential advantages of using this new energy device in a clinical aspect.

Translational Study on Recurrent Laryngeal Nerve Temperature Susceptibility

BACKGROUND

Recurrent laryngeal nerve (RLN) injury is the most common and serious complication after thyroid surgery. However, little is known about the temperature threshold leading to RLN injury. In this study, we investigated threshold temperatures that cause RLN injury during thyroid surgery using continuous intraoperative neuromonitoring in swine models.

METHODS

Four pigs weighing 30 to 40 kg were used for this study. We applied automatic periodic stimulation to the vagus nerve and dissected the RLN. The operative field was then filled with water at various temperatures (1.9°C to 87.4°C). The threshold temperature was defined as the temperature measured before filling the operative field that was associated with adverse events (latency increase of more than 10% or amplitude decrease of more than 50%). Loss of signal was defined as the electromyography (EMG) signal disappearing and not recovering during 30 min of observation.

RESULTS

The low and high threshold temperatures were 2.5°C and 81.5°C, respectively. There were no adverse events at surrounding temperatures between 5.9°C and 77.5°C. The EMG signals in the RLNs exposed to the low threshold temperatures recovered, and there was no loss of signal. In contrast, the RLNs that showed adverse events at the high threshold temperatures showed loss of signal and no recovery of EMG signals.

CONCLUSIONS

The RLN was found to be resistant to cold injury, whereas surrounding temperatures above 81.5°C may cause permanent thermal injury to the RLN. The surrounding temperature should be controlled within the safe range during thyroid surgery to avoid RLN injury.

Feasibility of Intraoperative Neuromonitoring During Thyroid Surgery Using Transcartilage Surface Recording Electrodes

BACKGROUND

Intraoperative neural monitoring (IONM) has gained widespread acceptance as an adjunct to the gold standard of visual identification of the recurrent laryngeal nerve (RLN) during thyroid surgery. Currently, laryngeal electromyography (EMG) recording during IONM is almost always performed using endotracheal tube (ETT) surface electrodes placed adjacent to vocal folds originating from the inner surface of the thyroid cartilage (TC). Therefore, it was hypothesized that surface recording electrodes placed on the outer surface of the TC should enable access to the EMG response of the vocal folds during IONM. The aim of this experimental study was to evaluate the feasibility of the transcartilage approach for laryngeal EMG recording during IONM.

METHODS

A porcine model (12 pigs and 24 RLN sides) with well established applicability in IONM research was used for the experiments. Both ETT electrodes adjacent to vocal folds and adhesive pre-gelled electrodes on the TC were used for EMG recording during IONM. Electrically evoked EMG signals detected by both electrode types were recorded and analyzed. EMG changes during tracheal displacement and RLN traction injury were compared.

RESULTS

Both the ETT and TC recording electrodes recorded typical laryngeal EMG waveforms evoked by a 1 mA stimulus current applied on both sides of the RLNs and vagus nerves (VNs). Under RLN stimulation, the mean EMG amplitudes recorded with the ETT and TC electrodes were 973 ± 79 μV and 695 ± 150 μV, respectively. Under VN stimulation, the mean amplitudes were 841 ± 163 μV and 607 ± 162 μV, respectively. When upward displacement of the trachea was experimentally induced, the TC electrodes showed less variation in recorded EMG signals compared to ETT electrodes. When RLN traction stress was experimentally induced, both the ETT and TC electrodes accurately recorded the typical EMG pattern of progressively degrading amplitude and gradual recovery after release of traction.

CONCLUSIONS

This study confirms the feasibility of using transcartilage surface electrodes for recording laryngeal EMG signals evoked during IONM in an animal model. However, before practical application of this approach in clinical thyroid surgery, further studies are needed to improve electrode designs by optimizing their shapes and sizes, and increasing their adhesive stability and sensitivity.

Transcutaneous Recording During Intraoperative Neuromonitoring in Thyroid Surgery

BACKGROUND

Recurrent laryngeal nerve (RLN) palsy remains a major source of morbidity after thyroid surgeries. Intraoperative neural monitoring (IONM) has gained increasing acceptance as an adjunct to standard practice of visual RLN identification. Endotracheal tube (ETT) surface recording electrodes systems are now widely used for IONM; however, a malpositioned ETT can cause false IONM results and requires time-consuming intraoperative verification of the ETT position and readjustment by the anesthesiologist. The aim of this experimental study was to evaluate the feasibility of the transcutaneous approach for recording evoked laryngeal electromyography (EMG) signals during IONM.

METHODS

A porcine model with well-established applicability in IONM research was used. Twelve piglets (24 nerve sides) were enrolled. Electrically evoked EMGs were recorded from surface electrodes on the ETT and from the adhesive pre-gelled surface electrodes on the anterior neck skin. The evoked EMG waveforms were measured and analyzed. The real-time signal stability of the electrodes during tracheal displacement and their accuracy in reflecting adverse EMG changes during RLN stress were evaluated during continuous IONM performed with automatic periodic vagus nerve (VN) stimulation.

RESULTS

In all nerves, both the ETT and neck adhesive skin electrodes successfully recorded typical evoked laryngeal EMG waveforms from the RLNs and VNs under stimulation with 1 mA. The transcutaneous electrodes recorded mean EMG amplitudes of 264 μV (±79) under RLN stimulation and 202 μV (±55) under VN stimulation. The electrodes recorded mean EMG latencies of 2.98 ms (±0.20) under RLN stimulation, 4.51 ms (±0.50) under right VN stimulation, and 8.13 ms (±0.94) under left VN stimulation, respectively. When tracheal displacement was experimentally induced, the EMG signals obtained by ETT electrodes varied significantly, but those obtained by transcutaneous electrodes did not. When RLN traction stress was experimentally induced, both ETT and transcutaneous electrodes recorded the same pattern of progressively degrading EMG amplitude with gradual recovery after release of traction.

CONCLUSIONS

This study confirms the feasibility of transcutaneous recording of evoked laryngeal EMG during IONM. Although this study confirms the stability and accuracy of the transcutaneous approach, it also revealed the need for new electrode designs to improve EMG amplitudes before practical clinical application of this approach.

Comparing the safety of harmonic ACE and ACE+ around the recurrent laryngeal nerve in swine models

Purpose

Among the various energy-based devices, ultrasonic shears are popular in thyroid surgeries. In this study, we tested the safety of Harmonic ACE and Harmonic ACE+ around the recurrent laryngeal nerve (RLN) in experimental swine models.

Methods

Harmonic ACE and Harmonic ACE+ were each tested in 4 piglets. Harmonic ACE and Harmonic ACE+ were activated at a 0- to 5-mm distance from the RLN. The function of the RLN was assessed using continuous electrophysiological monitoring.

Results

For Harmonic ACE, there was no adverse EMG event found when activated at 4- and 5-mm distances from the RLN. At a 2- to 3-mm distance, there were 4 adverse EMG events observed. In these 4 cases, adjacent tissue shrinkage occurred after 6 to 15 seconds of activation, and the RLN touched the Harmonic ACE. At a 1-mm distance, there were 2 adverse EMG events found after 25 seconds of activation. For Harmonic ACE+, there was no adverse EMG event observed when activated at 1- and 3-mm distances from the RLN. At a 0-mm distance, 2 adverse EMG events occurred after 6 to 10 seconds of activation.

Conclusion

The safe distance of Harmonic ACE and ACE+ was 4 and 1 mm, respectively, in the swine models. Harmonic ACE+ is safer than Harmonic ACE because it did not cause any tissue shrinkage. Surgeons need to understand the characteristics of devices for safe operation.

Comparison of surgical outcomes and complications between the Harmonic FOCUS and conventional surgery for open thyroidectomy

The aim of the present study was to evaluate the potential advantages of the ultrasonic scalpel compared with the conventional technique in thyroid surgery. Patients with resectable thyroid cancer and Basedow's disease were assigned to ultrasonic scalpel or conventional technique (knot-tying and electrocoagulation). The present study used the Harmonic FOCUS^® (HF) as an ultrasonic scalpel. Between February 2013 and May 2016, 45 patients were enrolled into the study. Duration of the surgery was significantly decreased in the HF group compared with the conventional surgery (CS) group (median 142 vs. 151 min; P=0.0406). Intraoperative blood loss and total volume of drainage fluid were significantly decreased in the HF group compared with the CS group (median 40 vs. 125 ml; P=0.0054, and median 120 vs. 175.5 ml; P=0.0490). Duration of drain placement and length of hospitalization stay were similar in the two groups. Furthermore, the overall incidence of postoperative complications did not differ between the two groups. Overall, the present study suggests that open thyroidectomy using the HF is safe and effective and not associated with any increase in complications.

Neural monitoring represent central safety asset for new technologies in thyroid surgery in translational protocols

Commentary on the published paper by Chávez KV, Barajas EM, Soroa F, Gamboa-Dominguez A, Ordóñez S, Pantoja JP, Sierra M, Velázquez-Fernández D, Herrera MF. Safety assessment of the use of ultrasonic energy in the proximity of the recurrent laryngeal nerve in a porcine model. Am J Surg. 2018 Jan;215(1):186-190. doi: 10.1016/j.amjsurg.2017.04.013. Epub 2017 Jun 7. PubMed PMID: 28622836.

Feasibility and safety of nerve stimulator attachment to energy-based devices: A porcine model study

BACKGROUND

Recently, several energy-based devices (EBDs) have been developed and applied in the context of thyroid surgery. EBDs can reduce operation time, blood loss, and postoperative pain. Compared to conventional electrocautery, EBDs operate at a relatively lower temperature and produce minimal lateral tissue damage. Yet, during device operation, the tip of the EBD is hot enough to cause thermal nerve damage, increasing the need for surgeons to be cautious about EBD application. To increase the safety of EBDs, we attached nerve stimulators to the tips of two EBDs and compared them to conventional monopolar nerve stimulation using a porcine model.

METHODS

Three piglets (30-40 kg) underwent total thyroidectomy after orotracheal intubation with a nerve integrity monitor (NIM) electromyography (EMG) endotracheal tube. Nerve stimulators were attached to two EBDs (Harmonic Focus^®+ and LigaSure™). After dissection and identification of six recurrent laryngeal nerves in the three piglets, both of the EBDs with attached nerve stimulators and a conventional monopolar nerve stimulator were applied near the nerve and EMG parameters were recorded using the NIM 3.0 system. The stimulus intensity was varied from 5 mA to 1 mA and the maximum distance and amplitude at which nerve detection was achieved were measured.

RESULTS

There were no statistically significant differences between the maximum distance or mean amplitude obtained from nerve stimulators attached to EBDs and those obtained from the conventional nerve stimulator. Additionally, there were no adverse EMG events related to the use of nerve stimulators attached to EBDs.

CONCLUSIONS

Attachment of a nerve stimulator to an EBD for nerve detection during thyroidectomy was as safe and effective as attachment of a conventional nerve stimulator. Use of a nerve stimulator attachment may reduce the likelihood of EBD-associated nerve damage during thyroid surgery.

Injury of the external branch of the superior laryngeal nerve in thyroid surgery

The external branch of the superior laryngeal nerve (EBSLN) innervates the cricothyroid muscle (CTM) to promote lengthening and thinning of the vocal fold, thus increasing voice pitch. The close relation with the superior thyroid vessels (STV) puts the EBSLN in risk every time the superior pole of the thyroid is dissected. It travels downward to innervate the CTM, lateral to the thyroid cartilage and to the inferior pharyngeal constrictor muscle (IPCM), being eventually covered by this muscle fibers as it approaches its entry point. During its descending course, the EBSLN curves and crosses the STV posteriorly. The lower this crossing occurs in the neck, the higher the risk of surgical damage to the nerve by transection, traction, entrapment, thermal damage or disrupted blood supply. The chances of surgical trauma are also increased by size and weight of the specimen, shorter neck length and non-white ethnicity. Voice changes following thyroid surgery are common and multifactorial. The actual rate of vocal impairment due to EBSLN injury is unclear, since changes to the everyday speaking voice can be minimal and laryngeal findings are usually subtle and controversial. CTM electroneuromyography (EMG) is the most accurate tool to diagnose abnormal EBSLN conductivity, but it is technically difficult and barely applicable in routine practice. Recommended approaches to prevent injury include: (I) individual distal ligature of the STV by the thyroid capsule; (II) visual identification of the nerve and its trajectory and (III) electrostimulation with either observation of CTM twitch or intraoperative nerve monitoring (IONM) via dedicated endotracheal tube electrodes. There is accumulating evidence that a combination of visual and standardized electrophysiological EBSLN identification with meticulous division of the STV improves preservation rates. IONM bears the additional benefits of prognostication, quantification and documentation of neural function once it allows intraoperative laryngeal EMG.

Safety assessment of the use of ultrasonic energy in the proximity of the recurrent laryngeal nerve in a porcine model

BACKGROUND

Advanced bipolar and ultrasonic energy have demonstrated reduction of operating time and blood loss in thyroidectomy. However, these devices generate heat and thermal dispersion that may damage adjacent structures such as the recurrent laryngeal nerve (RLN). This study was designed to evaluate the safety profile of the Harmonic Focus+^® (HF+) device through the evaluation of thermal injury to the RLN using different algorithms of distance and time with state of the art technology.

METHODS

25 Vietnamese pigs underwent activation of HF+ in the proximity of their RLN. They were divided into 4 groups according to activation distance (3 mm, 2 mm, 1 mm and on the RLN). Time of activation, time between tones of the ultrasonic generator, changes in the electromyographic signal using continuous nerve neuromonitoring, vocal fold mobility assessed by direct laryngoscopy and histological thermal damaged were evaluated.

RESULTS

None of the pigs had loss of signal in the electromyography during the procedure; only one pig had isolated transient decrease in amplitude and one increase in latency. One pig had transient vocal fold paresis in the group with activation on the nerve. Evaluation of the nerves by histology and immunohistochemistry did not show significant changes attributed to thermal injury.

CONCLUSIONS

The use of ultrasonic energy close to the RLN is safe, provided that activation time does not exceed the necessary time to safely transect the tissue.

Severity of Recurrent Laryngeal Nerve Injuries in Thyroid Surgery

BACKGROUND

Few studies in the literature have reported recovery data for different types of recurrent laryngeal nerve injuries (RLNIs). This study is the first attempt to classify RLNIs and rank them by severity.

METHODS

This prospective clinical study analyzed 281 RLNIs in which a true loss of signal was identified by intraoperative neuromonitoring (IONM), and vocal cord palsy (VCP) was confirmed by a postoperative laryngoscope. For each injury type, the prevalence of VCP, the time of VCP recovery, and physical changes on nerves were analyzed. Additionally, different RLNI types were experimentally induced in a porcine model to compare morphological change.

RESULTS

The overall VCP rate in at-risk patients/nerves was 8.9/4.6 %, respectively. The distribution of RLNI types, in order of frequency, was traction (71 %), thermal (17 %), compression (4.2 %), clamping (3.4 %), ligature entrapment (1.6 %), suction (1.4 %), and nerve transection (1.4 %). Complete recovery from VCP was documented in 91 % of RLNIs. Recovery time was significantly faster in the traction group compared to the other groups (p < 0.001). The rates of temporary and permanent VCP were 98.6 and 1.4 % for traction lesion, 72 and 28 % for thermal injury, 100 and 0 % for compression injury, 50 and 50 % for clamping injury, 100 and 0 % for ligature entrapment, 100 and 0 % for suction injury, and 0 and 100 % for nerve transection, respectively. Physical changes were noted in 14 % of RLNIs in which 56 % of VCP was permanent. However, among the remaining 86 % IONM-detectable RLNIs without physical changes, only 1.2 % of VCP was permanent. A porcine model of traction lesion showed only distorted outer nerve structure, whereas the thermal lesion showed severe damage in the inner endoneurium.

CONCLUSIONS

Different RNLIs induce different morphological alterations and have different recovery outcomes. Permanent VCP is rare in lesions that are visually undetectable but detectable by IONM. By enabling early detection of RLNI and prediction of outcome, IONM can help clinicians plan intra- and postoperative treatment.

Contribution of intraoperative neural monitoring to preservation of the external branch of the superior laryngeal nerve: a randomized prospective clinical trial

PURPOSE

The purpose of this study was to evaluate the effect of intraoperative neuromonitoring (IONM) on the injury rate of the external branch of the superior laryngeal nerve (EBSLN) during thyroidectomy.

METHODS

A total of 133 consenting patients (98 female, 35 male; mean age, 45.6 ± 11.7 years) undergoing thyroidectomy were randomly assigned to 2 groups. In group 1 (n = 65 patients, 105 nerves), superior thyroid pole dissection was performed with no attempt to identify the EBSLN; in group 2 (n = 68 patients, 106 nerves), IONM was used to identify the EBSLN during surgery. EBSLN function was evaluated by intraoperative electromyography of the cricothyroid muscle. The EBSLN Voice Impairment Index-5 (VII-5) was conducted preoperatively and at 1, 3, and 6 months postoperatively. The primary outcome was the prevalence of EBSLN injury. The secondary outcomes were the identification rate of the EBSLN using IONM and changes in postoperative voice performance.

RESULTS

EBSLN injury was detected in eight (12.3%) patients and nine (8.6%) nerves in group 1 and in one (1.5%) patient and one (0.9%) nerve in group 2 (patients, p = 0.015; nerves, p = 0.010). IONM contributed significantly to visual (p < 0.001) and functional (p < 0.001) nerve identification in group 2. The VII-5 indicated more voice changes in group 1 than 2 at 1, 3, and 6 months postoperatively (p = 0.012, p = 0.015, and p = 0.02, respectively).

CONCLUSION

IONM contributes to visual and functional identification of the EBSLN and decreases the rate of EBSLN injury during superior pole dissection. Routine use of IONM to identify the EBSLN will minimize the risk of injury during thyroidectomy.

Safety of energy based devices for hemostasis in thyroid surgery

Energy based devices (EBD) have been developed, implemented and increasingly applied in thyroid surgery because they can provide a combined dissection and haemostatic effect. In particular, advantages of EBD have been described in terms of efficacious haemostasis, reduction of procedure-associated time, reduced incision length, less operative blood loss and transfusion need, decreased postoperative drain, pain and hospital stay. In addition, EBD are essential for endoscopic procedures. On the contrary, a potential drawback is the increased health care costs. This paper reviews relevant medical literature published on the safety of new devices for achieving hemostasis and dissection around the recurrent laryngeal nerve (RLN).

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.

Safety of LigaSure in recurrent laryngeal nerve dissection-porcine model using continuous monitoring

OBJECTIVES/HYPOTHESIS

This study investigated recurrent laryngeal nerve (RLN) real-time electromyography (EMG) data to define optimal safety parameters of the LigaSure Small Jaw (LSJ) instrument during thyroidectomy.

STUDY DESIGN

Prospective animal model.

METHODS

Dynamic EMG tracings were recorded from 32 RLNs (16 piglets) during various applications of LSJ around using continuous electrophysiologic monitoring. At varying distances from the RLN, the LSJ was activated (activation study). The LSJ was also applied to the RLN at timed intervals after activation and after a cooling maneuver through placement on the sternocleidomastoid muscle (cooling study).

RESULTS

In the activation study, there was no adverse EMG event at 2 to 5 mm distance (16 RLNs, 96 tests). In the cooling study, there was no adverse EMG event after 2-second cooling time (16 RLNs, 96 tests) or after the LSJ cooling maneuver on the surrounding muscle before reaching the RLNs (8 RLNs, 24 tests).

CONCLUSION

Based on EMG functional assessment, the safe distance for LSJ activation was 2 mm. Further LSJ-RLN contact was safe if the LSJ was cooled for more than 2 seconds or cooled by touch muscle maneuver. The LSJ should be used with these distance and time parameters in mind to avoid RLN injury.

LEVEL OF EVIDENCE

N/A. Laryngoscope, 127:1724-1729, 2017.