Endotracheal Tube Electrodes Research Articles

Is trans-thyroid cartilage monitoring as good as endotracheal tube monitoring during thyroidectomy?

To evaluate whether trans-thyroid cartilage nerve monitoring for thyroid surgeries is as effective and safe as endotracheal tube monitoring. Fifty-one thyroidectomies (38 hemithyroidectomies and 13 total thyroidectomies, analyzed as two separate hemi-thyroidectomies) were included. Patients undergoing surgery from 6/2020 to 8/2021 were monitored simultaneously with the NIM® Nerve Monitoring System TriVantage™ Electromyography (EMG) endotracheal tube and EMG trans-thyroid cartilage. Electrophysiological responses of 64 vagus and recurrent laryngeal nerves were obtained. Peri-operative evaluation and 12-month post-operative follow-up were conducted to examine nerve function. Wilcoxon signed-rank and Spearman coefficient tests were used to determine whether there were differences between the methods. The average initial amplitude measured with the trans-thyroid cartilage method was higher in the recurrent laryngeal and vagus nerves (p = 0.002, p = 0.003, respectively). The mean difference in EMG amplitude from start to end of surgery for 10 damaged nerves (7 temporary and 3 permanent) differed from intact nerves in both methods and nerves (p < 0.05 for all). Among intact recurrent laryngeal nerves, 20.4% had 20-80% decrease in amplitude in endotracheal tube electrodes and 16.7% in trans-thyroid cartilage electrodes (p = 0.92). All cases with stable EMG signals or with increased EMG amplitude (with both types of electrodes and with both nerves) had normal post-operative vocal function. No significant difference was found between the two methods when measuring the vagus and recurrent laryngeal nerves. No complications occurred when using trans-thyroid cartilage electrodes. Trans-thyroid cartilage nerve monitoring for thyroid surgeries is as effective and safe as the current standard monitoring using an endotracheal tube. During thyroid surgery, patients are monitored to avoid damaging nerves near the vocal cords. This study compared monitoring through a throat tube with the easier method of monitoring outside of the throat to see if it is as effective and safe. No major difference was found between the two methods and there were no problems.

Various methods for intraoperative neural monitoring during thyroid surgery

Intraoperative neural monitoring (IONM) during thyroidectomy is an essential technique to safeguard the recurrent laryngeal nerve (RLN) and the external branch of the superior laryngeal nerve (EBSLN), both critical for vocal cord function. Utilizing electromyography (EMG), IONM provides real-time feedback on nerve integrity, significantly reducing the risk of nerve damage during surgery. The primary methods of IONM include endotracheal tube electrodes, surface electrodes, needle electrodes, and continuous monitoring, each with distinct advantages and limitations. Endotracheal tube electrodes offer direct measurements but can be difficult to position, while surface electrodes are non-invasive but may experience signal interference. Needle electrodes provide precise measurements but are invasive, and continuous monitoring offers ongoing feedback but requires advanced equipment. The evolution of IONM began in the mid-20th century and has progressed significantly, leading to its widespread adoption in thyroid surgery by the mid-2000s. Enhanced by recent technological advancements and standardized by professional guidelines, IONM has become integral in reducing postoperative complications. Ongoing research aims to further refine IONM techniques, ensuring optimal patient outcomes and the preservation of nerve function in thyroid surgery.

Noninvasive monitoring of the vagus nerve during thyroid surgery using cutaneous adhesive and needle electrodes: What is the optimal configuration?

Endotracheal tube (ETT) surface electrodes are used to monitor the vagus nerve (VN), recurrent laryngeal nerve (RLN), and external branch of the superior laryngeal nerve (EBSLN) during thyroid and parathyroid surgery. Alternative nerve monitoring methods are desirable when intubation under general anesthesia is not desirable or possible. In this pilot study, we compared the performance of standard ETT electrodes to four different noninvasive cutaneous recording electrode types (two adhesive electrodes and two needle electrodes) in three different orientations. The VN was stimulated directly during thyroid and parathyroid surgery using a Prass stimulator probe. Electromyographic (EMG) responses for each patient were recorded using an ETT plus one of the following four cutaneous electrode types: large-foot adhesive, small-foot adhesive, long-needle and short-needle. Each of the four electrode types was placed in three orientations: (1) bilateral, (2) ipsilateral mediolateral, and (3) ipsilateral craniocaudal. Four surgical cases were utilized for data collection with the repetitive measures obtained in each subject. Bilateral electrode orientation was superior to ipsilateral craniocaudal and ipsilateral mediolateral orientations. Regardless of electrodes type, all amplitudes in the bilateral orientation were >100 μV. When placed bilaterally, the small-foot adhesive and the long-needle electrodes obtained the highest EMG amplitudes as a percentage of ETT amplitudes. Cutaneous electrodes could potentially be used to monitor the VN during thyroid and parathyroid procedures. Different electrode types vary in their ability to record amplitudes and latencies. Bilateral orientation improves EMG responses in all electrode types. Additional validation of cutaneous electrodes as an alternative noninvasive method to monitor the VN is needed.

Optimization of electromyographic endotracheal tube electrode position by UEScope for monitored thyroidectomy.

ObjectiveProper position of an electromyographic (EMG) endotracheal tube within the larynx plays a key role in functional electrophysiologic intraoperative neural monitoring (IONM) in thyroid surgery. The purpose of this study was to determine the feasibility of a portable video‐assisted intubation device (UEScope) to verify the optimal placement of an EMG tube.MethodsA retrospective study enrolled 40 consecutive patients who underwent monitored thyroidectomies. After positioning the patient for surgery, an anesthesiologist performed tracheal intubation with UEScope and checked the position of the tube at the proper depth without rotation to the vocal cords. The main outcome measured was the proper EMG tube position, free from further adjustment. The secondary outcomes assessed were the percentage of available initial vagal stimulation (V1) signals.ResultsAll tracheal intubations were successful at first attempt. Proper EMG tube placement without position adjustment was found in 97.5% of the patients. Tube withdrawal was required in a male patient. All patients obtained detectable V1 signals; the lowest and median V1 amplitude was 485 and 767 μV as a reference value, respectively.ConclusionThe UEScope is a valuable and reliable tool for placing an EMG tube and confirming its position during monitored thyroidectomy. In addition, further tube adjustment might be waived in most cases when the anesthesiologist placed the EMG tube after patient positioning for surgery. Routine use of video‐assisted intubation devices is highly recommended.Level of Evidence4.

Proprieties of adhesive surface arrays to thyroid cartilage for recurrent laryngeal nerve monitoring.

BackgroundTo investigate the optimal placement and size of adhesive thyroid cartilage electrodes (ATCEs) placed on the thyroid cartilage in porcine models for evaluating recurrent laryngeal nerve function compared with the other 3 recording electrode types.MethodsFour Meishan piglets were used for this study. The electromyogram (EMG) signal stability was detected by intraoperative nerve monitoring (IONM). Best location and size of ATCEs were detected, and the EMG signals from each were compared. Latency data were tested by stimulating the different nerve points, and 6 manipulations of the trachea and endotracheal tube (ET) were applied to test the stability of EMG signals. ET electrodes, needle electrodes, and transcutaneous recording electrodes were simultaneously tested with comparison to ATCEs.ResultsThe optimal placement locations and sizes of ATCEs were determined. The amplitudes and latencies recorded from the ATCEs were consistent with those of the ET electrodes. More anti-interference was observed with the ATCEs than with the ET electrodes in surgical manipulations. ATCEs could be used during intermittent and continuous monitoring in similar fashion to ET electrodes and needle electrodes.ConclusionsATCEs had consistent monitoring function with ET electrodes and needle electrodes. Feasibility, EMG stability, and optimal location and size of ATCEs for IONM were resolved. The EMG profiles from the ATCEs were more stable during surgical manipulations.

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.

Intraoperative Monitoring for Vagus Nerve Stimulation

Vagus nerve stimulation is a palliative treatment for patients with refractory epilepsy; however, the misplacement of electrodes may cause complications and thus needs to be avoided. We herein report an intraoperative monitoring technique to prevent the misplacement of electrodes. Endotracheal tube electrodes were inserted to record electromyographic activity from the vocal cords and identify the vagus nerve. Electromyography electrodes were placed on the sternomastoid muscle, sternohyoid muscle, geniohyoid muscle, and trapezius muscle to record muscle activities innervated by the ansa cervicalis. The vagus nerve and ansa cervicalis were electrically stimulated during surgery, and electromyography of the vocal cords and muscles innervated by the ansa cervicalis was recorded. The threshold of vagus nerve activation ranged between 0.05 and 0.75 mA. The vagus nerve was successfully identified and differentiated from the nerve root of the ansa cervicalis using this technique. Intraoperative monitoring of the vagus nerve and ansa cervicalis is useful for safe and effective vagus nerve stimulation.

Investigation on EMG Profiles of the Superior Laryngeal Nerve in a In Vivo Porcine Model

Background: The electromyographic (EMG) profiles of external branch of the superior laryngeal nerve (EBSLN) have been defined and the optimal intensity of the stimulation of EBSLN in an in vivo porcine model has been explored. Materials: EMG was simultaneously registered by the surface of endotracheal tube and needle electrodes by applying a monopolar stimulation probe in 12 piglets (22 EBSLNs). Vagal nerve (VN), RLN and EBSLN were excited to record the EMG tracings and cricothyroid muscle twitch (CTM). VN, RLN and EBSLN were stimulated from 0.1 to 1.0 mA. Cmin and Cmax have been defined as the minimum and maximal stimulation to evoke an EMG response. Results: The stimulation resulted in a dose-response curve. Cmin were 0.19 mA (0.04–0.4), 0.19 mA (0.08–0.3) and 0.21 mA (0.1-0.4) for EBSLN, RLN and VN (p > 0.05) respectively. Cmax were 0.6 mA along with an amplitude value of 396 ± 330 μV, 0.5 mA including 1058 ± 382 μV, 0.8 mA coupled with 870 ± 382 μV, equally for EBSLN, RLN and VN (p > 0.05) respectively. No asymmetry of amplitude responses each side for EBSLN, RLN and VN (p = 0.317, p = 0.203 and p = 0.468, respectively) was noted. The amplitudes of EBSLN were significantly lower than RLNs and VN (42% of RLN and 50% of VN amplitude rates). Also, CTM twitch was always detectable with the stimulation of EBSLN. Conclusions: Cmin and Cmax of EBSLN were comparable to RLN and VN standards. The amplitude stimulus-response curves of RLN, VN and EBSLN were highly variable. It has been suggested to apply a stimulation of 1.0 mA and a visual appreciation of CTM twitch for the identification of EBSLN.

Anterior laryngeal electrodes for recurrent laryngeal nerve monitoring during thyroid and parathyroid surgery: New expanded options for neural monitoring.

Intraoperative neural monitoring is a useful adjunct for the laryngeal nerve function assessment during thyroid and parathyroid surgery. Typically, monitoring is performed by measurement of electromyographic responses recorded by endotracheal tube (ETT) surface electrodes. Tube position alterations during surgery can cause displacement of the electrodes relative to the vocal cords, leading to false positive loss of signal. Numerous reports have denoted monitoring equipment-related issues, especially endotracheal tube displacement, as the dominant source of false positive error. The false positive error may result in inappropriate decisions by the surgeon. This study tests the hypothesis that anterior laryngeal electrodes (ALEs) can help reduce this error. Placement of ALEs directly onto the thyroid cartilage represent an adjunctive and possible alternative method to standard ETT surface electrodes. Retrospective review. Fifteen consecutive patients undergoing thyroid and parathyroid surgery with intraoperative neuromonitoring using both ETT electrodes and ALEs were studied. Data collected included site of neural stimulation, laterality, and electromyographic parameters. With vagal and recurrent laryngeal nerve stimulation, the ALEs recorded mean vocalis muscle waveform amplitude within 83% of that recorded with standard ETT electrodes. The latency measurements with the anterior laryngeal and endotracheal electrodes were similar, with both electrodes recording significantly longer latency for the left vagus nerve as compared to the right vagus nerve. With superior laryngeal nerve stimulation, the ALEs recorded a 800% greater mean amplitude than the ETT electrodes. The ALEs demonstrated similar sensitivity to stimulation at low current as ETT electrodes and provided stable intraoperative monitoring information. Compared to ETT surface electrodes, the ALEs provide similar and stable electromyographic responses with equal sensitivity for recording evoked responses during neural monitoring in thyroid and parathyroid surgery. The ALEs offer significantly more robust monitoring of the external branch of the superior laryngeal nerve. Furthermore, ALEs are contained within the operative field, are totally surgeon controlled, and are unaffected by the potential vicissitudes of ETT position during surgery. 4 Laryngoscope, 128:2910-2915, 2018.

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

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. 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. 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. 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.

Experimental study of needle recording electrodes placed on the thyroid cartilage for neuromonitoring during thyroid surgery.

Needle electrodes placed on the thyroid cartilage (TC) are an alternative to endotracheal tube (ET) electrodes for assessing recurrent laryngeal nerve (RLN) function during thyroid surgery. Needle electrodes placed on the TC were evaluated in an experimental porcine model. Continuous intraoperative neuromonitoring was used to record the electromyogram. Each TC side was delineated into nine areas to determine the optimal placement of the electrode, and needle electrode area, depth and orientation for optimal electromyographic (EMG) amplitudes were evaluated. RLN root locations were stimulated at four locations: vagus nerve distal to the neuromonitoring electrode, and most proximal, middle and laryngeal entry points of the nerve. A nerve retraction injury model was adapted to compare RLN monitoring by TC versus ET electrodes. An optimal site for placement of needle electrodes was identified, and electromyograms obtained from the various needle insertion depths and orientations were similar. Latencies recorded from the TC and ET electrodes were similar. The amplitude profile of TC electrodes responded earlier to RLN injury than that of ET electrodes. Amplitude and drop to loss of signal were also registered earlier. EMG amplitudes obtained using TC electrodes were higher, and identified RLN injury earlier than ET electrodes. Surgical relevance Needle electrodes placed on the thyroid cartilage (TC) are an alternative to endotracheal tube (ET) electrodes for assessing the function of the recurrent laryngeal nerve (RLN) in thyroid surgery. This study used an experimental porcine model to evaluate the use of needle electrodes inserted in the TC, compared with ET electrodes, for producing an electromyographic (EMG) profile of the RLN. Nine areas of the TC, with various needle insertion depths and orientations, were compared. Perichondral insertion into the avascular area of the TC was found to be safe. The EMG amplitude and latency features recorded via the TC and ET electrodes were compared, using both intermittent and continuous monitoring. Changes in EMG amplitudes in response to nerve traction injury were registered earlier with TC electrodes than with ET electrodes, and the amplitudes were higher and more stable. Latencies obtained via the TC and ET electrodes were similar. These results indicate that the development of a non-invasive monitoring electrode with improved function, easy placement and low cost is possible.

Human laryngeal sensory receptor mapping illuminates the mechanisms of laryngeal adductor reflex control

The laryngeal adductor reflex (LAR) is an airway protective response triggered by sensory laryngeal receptors. It is unknown whether different glottic and supraglottic subsites vary in their reflex elicitation abilities. The recent discovery that a bilateral LAR is present in humans under general anesthesia upon laryngeal mucosal stimulation has enabled us to map the sensory receptor density for LAR elicitation at different laryngeal subsites. Our findings expose the likely mechanisms of LAR control. Prospective series of 10 patients undergoing laryngoscopy. Laryngeal subsites (epiglottic tip, membranous vocal fold, midventricular vocal fold, posterior supraglottis, epiglottic petiole) were stimulated via direct laryngoscopy with a bipolar probe. Vocal fold responses were recorded by endotracheal tube and hook wire electrodes, and visual observation. Posterior supraglottic stimulation elicited bilateral LARs in all patients at all intensities. Membranous vocal folds, epiglottic petiole, and subglottis elicited no LAR. Ventricular fold and epiglottic tip responses converted from ipsi- to bilateral at high intensities. There are likely three checkpoints for control of the LAR in humans. These checkpoints protect against inappropriate LAR activation during volitional tasks without compromising airway protection: 1) topographical differences in receptor density with the highest density in subsites most likely to contact foreign substances; 2) absence of receptors in membranous vocal folds; and 3) central summation threshold for crossed interneuron activation at brainstem level where only strong intensity stimuli will elicit bilateral responses. Checkpoint dysfunction provides a novel framework to diagnose and treat disease processes, including aspiration, laryngospasm, and sudden infant death. 4. Laryngoscope, E365-E370, 2018.

Transcutaneous Recording During Intraoperative Neuromonitoring in Thyroid Surgery.

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. 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. 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. 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.

Noninvasive, tube-based, continuous vagal nerve monitoring using the laryngeal adductor reflex: Feasibility study of 134 nerves at risk.

Continuous vagal intraoperative neuromonitoring (IONM) currently requires placement of a vagal nerve electrode. Herein, we present data from 100 patients (134 nerves-at-risk) monitored continuously during neck endocrine surgeries using a noninvasive, new methodology that solely utilizes endotracheal tube electrodes to simultaneously stimulate laryngeal mucosa and record a laryngeal adductor reflex continuous IONM (LAR-C-IONM) response. The laryngeal adductor reflex (LAR) was elicited by electrical laryngeal mucosal stimulation on the side contralateral to the operative field using endotracheal tube electrodes. All patients completed preoperative and postoperative laryngeal and voice examinations. One hundred patients (134 nerves-at-risk) were included. Significantly more nerves-at-risk with an LAR opening to closing amplitude decrement >60% or with absolute closing amplitude <100 μV had postoperative vocal fold paralysis (P < .001). The LAR-C-IONM was highly sensitive to recurrent laryngeal nerve (RLN) stretch or compression. The LAR-C-IONM is a promising new way to perform continuous vagal monitoring that requires no equipment other than an electromyography (EMG) endotracheal tube and is undergoing further, large-scale evaluation.

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.

Contralateral R1 and R2 components of the laryngeal adductor reflex in humans under general anesthesia

To demonstrate that under total intravenous general anesthesia (TIVA), the contralateral R1 (cRI) and contralateral R2 (cR2) components of the laryngeal adductor reflex (LAR) can be reliably elicited; to determine effects of topical anesthesia and inhalational anesthesia on the LAR; and to discuss how this technique may be utilized to continuously monitor the vagus nerve reflex arc. Case series. Vocal fold mucosa was electrically stimulated via endotracheal tube surface-based electrodes to elicit a LAR. Responses were recorded using the endotracheal tube electrode contralateral to the simulating electrode for each side. Twenty-one patients (31 nerves at risk), aged between 28 to 84 years, who underwent thyroid and cervical spine surgeries (4 males, 17 females) were included. cR1 responses were reliably elicited in all patients, and cR2 responses were obtained in 14 patients (66.6%). Mean cR1 latencies ± standard deviation were 22.5 ± 2.5 milliseconds (ms) (left) and 23.4 ± 3.3 ms (right). Mean cR1 amplitudes were 237.9 ± 153.9 microvolts (uV) (left) and 265.0 ± 226.5 uV (right). Mean R2 latencies were 59.8 ± 4.9 ms (left) and 61.8 ± 7.9 ms (right). Intraoperative reversible cR1 amplitude decreases correlated temporally with surgical maneuvers stretching or compressing the RLN or internal branch of the superior laryngeal nerve (iSLN). Inhalational anesthetic agents abolished cR2 and minimized cR1 at mean alveolar concentrations > 0.5. Topical lidocaine significantly reduced LAR amplitude. LAR cR1 and cR2 responses are present in humans under TIVA and may afford some airway protection against aspiration under anesthesia. They are inhibited by inhalational anesthetics and topical lidocaine. Continuous intraoperative iSLN and RLN monitoring are possible using surface-based endotracheal tube electrodes alone to stimulate and record cR1 responses. 4. Laryngoscope, 127:E443-E448, 2017.

Comparison of EMG signals recorded by surface electrodes on endotracheal tube and thyroid cartilage during monitored thyroidectomy

A variety of electromyography (EMG) recording methods were reported during intraoperative neural monitoring (IONM) of recurrent laryngeal nerve (RLN) in thyroid surgery. This study compared two surface recording methods that were obtained by electrodes on endotracheal tube (ET) and thyroid cartilage (TC). This study analyzed 205 RLNs at risk in 110 patients undergoing monitored thyroidectomy. Each patient was intubated with an EMG ET during general anesthesia. A pair of single needle electrode was inserted obliquely into the TC lamina on each side. Standard IONM procedure was routinely followed, and EMG signals recorded by the ET and TC electrodes at each step were compared. In all nerves, evoked laryngeal EMG signals were reliably recorded by the ET and TC electrodes, and showed the same typical waveform and latency. The EMG signals recorded by the TC electrodes showed significantly higher amplitudes and stability compared to those by the ET electrodes. Both recording methods accurately detected 7 partial loss of signal (LOS) and 2 complete LOS events caused by traction stress, but only the ET electrodes falsely detected 3 LOS events caused by ET displacement during surgical manipulation. Two patients with true complete LOS experienced temporary RLN palsy postoperatively. Neither permanent RLN palsy, nor complications from ET or TC electrodes were encountered in this study. Both electrodes are effective and reliable for recording laryngeal EMG signals during monitored thyroidectomy. Compared to ET electrodes, TC electrodes obtain higher and more stable EMG signals as well as fewer false EMG results during IONM.

A novel methodology for assessing laryngeal and vagus nerve integrity in patients under general anesthesia.

To describe a novel methodology for intraoperative neuro-monitoring of laryngeal and vagus nerves by utilizing the laryngeal adductor reflex (LAR). Case series of 15 patients undergoing thyroid and cervical spine surgeries under total intravenous general anesthesia. Vocal fold mucosa was electrically stimulated to elicit a LAR using endotracheal tube based electrodes. Contralateral R1 (cR1) and R2 (cR2) responses were recorded using the endotracheal tube electrode contralateral to the simulating electrode. The LAR was reliably elicited in 100% of patients for the duration of each surgical procedure. Mean onset latency of cR1 response was 22.4±2.5ms (right) and 22.2±2.4ms (left). cR2 responses were noted in 10 patients (66.7%). No peri-operative complications or adverse outcomes were observed. The LAR is a novel neuro-monitoring technique for the vagus nerve. Advantages over current monitoring techniques including simplicity, ability to continuously monitor neural function without placement of additional neural probes and ability to assess integrity of both sensory and motor pathways. The LAR represents a novel method for intraoperatively monitoring laryngeal and vagus nerves. The LAR monitors the entire vagus nerve reflex arc and is thus applicable to all surgeries where vagal nerve integrity may be compromised.

36. Monitoring motor evoked potentials of vagus nerve with endotracheal tube electrodes in brainstem surgery

In surgery around brainstem for preservation of swallowing function, monitoring of the corticobulbar tract of the X cranial nerve – and not only vagal rootlets – is needed. A few researchers have studied intraoperative monitoring of the vagus nerve corticobulbar pathway. In the past, X nerve has been monitored using needle or hook-wire electrodes, endoscopically or laryngoscopically placed in the vocal fold. Because of their complexity and invasiveness, these techniques have not been widely used. New studies with vagal MEPs have been recently published, although they required needle insertion into the vocal cord. Reports with non-invasive methods are still lacking. In this work we report our series of vagal nerve motor evoked potentials using endotracheal adhesive electrode in surgery around brainstem. In 26 patients who have undergone surgery around brainstem vocal cord MEPs were recordable in about 70% of cases. Correct electrode placement is the main issue to obtain signals. Latencies varied from 14 to 20 msec and amplitude from 40 to 200 uv. In 3 cases there was MEP loss and the patients suffered of post operative dysphagia. MEP recorded with endotracheal tube adhesive electrodes is a safe, effective and reliable method to monitor corticobulbar vagal tract.

Evaluating the introduction of intraoperative neuromonitoring of the recurrent laryngeal nerve in thyroid and parathyroid surgery.

IntroductionParesis of the recurrent laryngeal nerve (RLN) is a complication of thyroid surgery. Neuromonitoring as is gaining acceptance among surgeons. The aim of the study was to assess the number of technical problems in the initial phase of intraoperative neuromonitoring (IONM) use and the specificity, sensitivity, positive predictive value and negative predictive value of neuromonitoring. The number of cases of postoperative paresis (transient and permanent) was assessed.Material and methodsThe prospective analysis included 101 thyroid operations with IONM (190 RLNs at risk of injury) in the period from January to April, 2012. Demographic data, rate of RLN identification, sensitivity, specificity and predictive value of the method, the duration of the procedurę and the percentage of RLN paresis were considered.ResultsThe RLN was identified in 92% of the cases. Technical problems were observed in 12.98%, of which 61% were due to incorrect positioning of the endotracheal tube electrodes in relation to the vocal cords. The sensitivity, specificity, negative and positive predictive value and the accuracy of the method were respectively 71%, 98%, 62.5%, 98.9% and 97%. Early nerve injury occurred in 3.7% of the cases; 2.6% were temporary paresis and 1.1% permanent.ConclusionsDuring the initial stages of implementing IONM we experienced technical problems that required correction in every tenth patient. The positive predictive value was relatively low; nevertheless, good results in terms of the rate of accurate identification of the RLN as well as the low rate of RLN paresis support the use of this method.