Endotracheal Tube Surface Electrodes Research Articles

The use of thyroid cartilage needle electrodes in intraoperative neuromonitoring during thyroidectomy: Case-control study.

The most commonly used recording-side method in intraoperative neural monitoring (IONM) detects the stimulus with the endotracheal tube surface (ETS) electrodes placed in the endotracheal tube during thyroidectomy. The thyroid cartilage needle (TCN) electrode method is an alternative recording-side system in IONM. This study compared two recording-side techniques in IONM. Data were retrospectively analyzed from 885 patients who underwent thyroidectomy between January 2012 and December 2020, with 110 ETS and 775 TCN electrodes. Patients' demographics, diagnosis, surgery type, and amplitudes of all stimulation steps were compared. Costs per patient were calculated. No significant differences were found in the demographic data between the two groups. All amplitudes were higher in the IONM system where TCN electrodes were used than that with ETS electrodes (all stimulation steps p < 0.001, except left-V2 p=0.007). Further, TCN electrodes were 20 times cheaper than the ETS electrodes. TCN electrodes are an inexpensive and efficient alternative to ETS electrodes in IONM.

Neuromonitored Thyroid Surgery: Optimal Stimulation Based on Intraoperative EMG Response Features.

To evaluate/compare normative electrophysiologic electromyography (EMG) response characteristics of recurrent laryngeal, vagus, and external branch of superior laryngeal nerve evoked with different stimulators used in neuromonitored thyroid surgery. Prospective crossover study METHODS: EMG responses obtained via endotracheal tube surface electrodes in 11 patients undergoing thyroid surgery were recorded when stimulated with four stimulators: two monopolar (Prass standard and ball tip), one bipolar, and one dissecting instrument. Normative mean EMG results including latency, amplitude, threshold, saturation currents, and distance-sensitivity were compared. The Prass standard stimulator had shorter latency time when nerve was not covered with fascia (P = .04). The bipolar, dissecting instrument, and ball tip demonstrated similar latency times with and without nerve fascia. Pooled mean latency increased significantly from 1.86 ms to 2.16 ms when comparing nerves without fascia and nerves with fascia (P < .05). The Prass standard monopolar stimulator had the lowest mean threshold at 0.40 mA, with the dissecting instrument having the highest threshold at 0.89 mA for dissected nerve. Pooled mean threshold and saturation increased from 0.6 mA to 1.7 mA (P < .0001) and 1.57 mA to 4.15 mA (P < .001) with fascia covering nerve, respectively. The mean depolarization rate was 100% for monopolar and bipolar electrodes and 81% for dissecting instrument at 1 mA. Only 9% of monopolar electrodes generated an EMG response when stimulated from 2 mm away. Monopolar stimulators are more sensitive for neural mapping, whereas bipolar instruments are more specific, thus reducing false positive stimulation. Dissecting instruments share many features of monopolar stimulators while being more specific, and thus are a viable alternative. 2b Laryngoscope, 2020.

Anesthetic Considerations of Intraoperative Neuromonitoring in Thyroidectomy.

Intraoperative neuromonitoring (IONM) might reduce the incidence of injury to the recurrent laryngeal nerve (RLN) during thyroidectomy. Although dislocation of endotracheal tube surface electrodes can lead to false-positive IONM results (loss of signal), the risk factors for dislocation and the effects of muscle relaxants are unclear. Therefore, to identify factors that affect IONM results, we examined the frequency and risk factors for tube dislocation after cervical extension before surgery, the effect of sugammadex administration, and the correlation between IONM results and postoperative RLN palsy. Thirty-nine patients scheduled for thyroidectomy from October 2016 to April 2017 were enrolled. All patients underwent standard IONM and pre- and postoperative laryngoscopy. Differences in patient characteristics in the tube dislocation group and non-dislocation group, and differences in amplitude during vagal stimulation before and after sugammadex administration, were assessed by the Mann-Whitney test or Fisher's exact test. Tube dislocation occurred in 27 patients (69%). Sterno-cricoid distance was significantly shorter in the dislocation group (n=27) than in the non-dislocation group (n=12) (43.88 [32.2-55.91] mm vs 49.46 [40.66-55.91] mm, respectively; p=0.048). Without sugammadex, amplitude during vagal stimulation was sufficient for monitoring. Nine patients had new-onset RLN palsy, which was transient in all patients. The sensitivity of IONM was 100%, the positive predictive value was 60%, and the negative predictive value was 100%. The present findings suggest that anesthesiologists should use video laryngoscopy to correct tube dislocation and that a rocuronium dose of 0.6 mg/kg, without sugammadex, is adequate for IONM.

Monitoring of the posterior cricoarytenoid muscle represents another option for neural monitoring during thyroid surgery: Normative vagal and recurrent laryngeal nerve posterior cricoarytenoid muscle electromyographic data.

Intraoperative neural monitoring (IONM) of laryngeal nerves using electromyography (EMG) is routinely performed using endotracheal tube surface electrodes adjacent to the vocalis muscles. Other laryngeal muscles such as the posterior cricoarytenoid muscle (PCA) are indirectly monitored. The PCA may be directly and reliably monitored through an electrode placed in the postcricoid region. Herein, we describe the method and normative data for IONM using PCA EMG. Retrospective review. Data were reviewed retrospectively for thyroid and parathyroid surgery patients with IONM of laryngeal nerves from January to August 2016. Recordings of vocalis and PCA EMG amplitudes and latencies with stimulation of laryngeal nerves were obtained using endotracheal (ET) tube-based and postcricoid surface electrodes. Data comprised EMG responses in vocalis and PCA recording channels with stimulation of the vagus, recurrent laryngeal nerve (RLN), and external branch of the superior laryngeal nerve from 20 subjects (11 left, 9 right), as well as PCA EMG threshold data with RLN stimulation from 17 subjects. Mean EMG amplitude was 725.69 ± 108.58 microvolts (µV) for the ipsilateral vocalis and 329.44 ± 34.12 µV for the PCA with vagal stimulation, and 1,059.75 ± 140.40 µV for the ipsilateral vocalis and 563.88 ± 116.08 µV for the PCA with RLN stimulation. There were no statistically significant differences in mean latency. For threshold cutoffs of the PCA with RLN stimulation, mean minimum and maximum threshold intensities were 0.37 milliamperes (mA) and 0.84 mA, respectively. This study shows robust and reliable PCA EMG waveforms with direct nerve stimulation. Further studies will evaluate feasibility and application of the PCA electrode as a complementary quantitative tool in IONM. 4. Laryngoscope, 128:283-289, 2018.

Changes in electromyographic amplitudes but not latencies occur with endotracheal tube malpositioning during intraoperative monitoring for thyroid surgery: Implications for guidelines

During intraoperative neural monitoring (IONM) in thyroid and parathyroid surgery, endotracheal (ET) tube migration can result in a decrease in vocalis electromyographic (EMG) amplitude without a concordant latency elevation during stimulation of the recurrent laryngeal nerve (RLN). Retrospective review. Data were reviewed retrospectively for thyroid and parathyroid surgery patients with IONM of the laryngeal nerves from January 2015 to December 2015. Recordings of vocalis EMG amplitudes and latencies with RLN stimulation were obtained with the neuromonitoring ET tube surface electrodes in optimal baseline position, with vertical displacement away from the vocalis, and with rotational change away from baseline. ET tube surface electrode EMG recordings were obtained with stimulation of seven left and three right RLNs in a total of 10 patients. Mean vocalis EMG amplitudes were reduced with vertical displacement 1 and 2 cm both inferior and superior to baseline and with rotational change (45° and 90° clockwise and counterclockwise, 180°), although amplitude change with 45° clockwise and 180° rotation did not meet statistical significance. Mean EMG latency values did not change significantly from baseline with either rotation or vertical displacement of the ET tube. An isolated decrease in EMG amplitude without concordant latency elevation should warrant re-evaluation of ET tube position during thyroid and parathyroid surgery and is in contrast to a combined event, with both EMG amplitude decrease and concordant latency increase, which is more suggestive of a true neuropraxic injury. 4. Laryngoscope, 127:2182-2188, 2017.

The functional role of the pharyngeal plexus in vocal cord innervation in humans.

Classical understanding of the function of the pharyngeal plexus in humans is that it relies on both motor branches for innervation of the majority of pharyngeal muscles and sensory branches for the pharyngeal wall sensation. To date there has been no reported data on the role of the pharyngeal plexus in vocal cord innervation. The aim of this study is to evaluate whether or not the plexus pharyngeus contributes to the innervation of the vocal cords. One hundred twenty-five sides from 79 patients (59 female, 20 male) undergoing thyroid surgery with intraoperative neuromonitoring were prospectively evaluated. While vocal cord function was evaluated with endotracheal tube surface electrodes, cricothyroid and cricopharyngeal muscle electromyographic recordings were obtained with a pair of needle electrodes. The ipsilateral pharyngeal plexus, external branch of the superior laryngeal nerve, and recurrent laryngeal nerve were stimulated with a monopolar probe at 1mA. With stimulation of the plexus pharyngeus on 125 operated sides, positive electromyographic waveforms were detected from five ipsilateral vocal cords (accounting for 3.2% of all vocal cords monitored and 6.3% of patients). The mean EMG amplitude of the vocal cords with stimulation of the plexus pharyngeus was 147±35.5 μV (range 110-203). In one case, the long latency time of 19.8ms correlated with innervation by the glottic closure reflex pathway. The short latencies seen in the other four cases [3.9±1.1ms (range 3.2-5.5)] correlated with direct innervation. In some cases, the plexus pharyngeus may contribute to vocal cord innervation by reflex or direct innervation patterns in humans.

Intraoperative electrophysiologic monitoring of the recurrent laryngeal nerve during thyroid and parathyroid surgery: Experience with 1,381 nerves at risk.

The electrophysiologic responses of 1,381 recurrent laryngeal nerves (RLN) during monitored neck surgery were recorded and reviewed. Retrospective case series. With institutional review board approval, we reviewed thyroid and other neck surgeries performed with intraoperative nerve monitoring (IONM) between the years 1995 and 2006. This list yielded consecutively monitored 1,381 RLNs, with over 3,000 hours of monitoring experience. All patients underwent preoperative and postoperative laryngoscopy. In an initial subset of patients, both hook-wire and endotracheal tube (ETT) surface electrodes were utilized. Normative stimulation parameters; postoperative vocal cord function prognostication using monitoring data; and false-positive, false-negative, and passive electrophysiologic responses were evaluated RESULTS: Hook-wire electrodes and ETT surface electrodes were found to have good correlation in terms of amplitude (correlation coefficient, R = 0.89). Nerve stimulation of 1 to 2 mA resulted in an ipsilateral biphasic response, with 3.3 ms mean latency and 900 μV mean amplitude. Permanent and temporary RLN paralysis rates were 0% and 0.7%, respectively. Specificity of electromyography (EMG) loss of signal (LOS) postoperative vocal cord paralysis (VCP) detection was 99.9%, and sensitivity was 33%. Negative predictive value of EMG LOS at the end of surgery in the prediction of postoperative VCP was 99.6%, whereas its positive predictive value for VCP was 75%. Intraoperative nerve monitoring of the RLN during thyroid and other neck surgeries can aid in the nerve mapping, nerve identification, and prognostication of postoperative vocal cord function, which in turn can influence the surgeon's decision to proceed to bilateral surgery. 4. Laryngoscope, 127:280-286, 2017.

Intraoperative Mapping and Monitoring for Rootlets of the Lower Cranial Nerves Related to Vocal Cord Movement.

Damage to the motor division of the lower cranial nerves that run into the jugular foramen leads to hoarseness, dysphagia, and the risk of aspiration pneumonia; therefore, its functional preservation during surgical procedures is important. Intraoperative mapping and monitoring of the motor rootlets at the cerebellomedullary cistern using endotracheal tube electrodes is a safe and effective procedure to prevent its injury. To study the location of the somatic and autonomic motor fibers of the lower cranial nerves related to vocal cord movement. Twenty-four patients with pathologies at the cerebellopontine lesion were studied. General anesthesia was maintained with fentanyl and propofol. A monopolar stimulator was used at amplitudes of 0.05 to 0.1 mA. Both acoustic and visual signals were displayed as vocalis muscle electromyographic activity using endotracheal tube surface electrodes. The average number of rootlets was 7.4 (range, 5-10); 75% of patients had 7 or 8 rootlets. As many as 6 rootlets (2-4 in most cases) were responsive in each patient. In 23 of the 24 patients, the responding rootlets congregated on the caudal side. The maximum electromyographic response was predominantly in the most caudal or second most caudal rootlet in 79%. The majority of motor fibers of the lower cranial nerves run through the caudal part of the rootlets at the cerebellomedullary cistern, and the maximal electromyographic response was elicited at the most caudal or second most caudal rootlet. EMG, electromyographic.

Motor evoked potential monitoring of the vagus nerve with transcranial electrical stimulation during skull base surgeries

Dysphasia is one of the most serious complications of skull base surgeries and results from damage to the brainstem and/or cranial nerves involved in swallowing. Here, the authors propose a method to monitor the function of the vagus nerve using endotracheal tube surface electrodes and transcranial electrical stimulation during skull base surgeries. Fifteen patients with skull base or brainstem tumors were enrolled. The authors used surface electrodes of an endotracheal tube to record compound electromyographic responses from the vocalis muscle. Motor neurons were stimulated using corkscrew electrodes placed subdermally on the scalp at C3 and C4. During surgery, the operator received a warning when the amplitude of the vagal motor evoked potential (MEP) decreased to less than 50% of the control level. After surgery, swallowing function was assessed clinically using grading criteria. In 5 patients, vagal MEP amplitude permanently deteriorated to less than 50% of the control level on the right side when meningiomas were dissected from the pons or basilar artery, or when a schwannoma was dissected from the vagal rootlets. These 5 patients had postoperative dysphagia. At 4 weeks after surgery, 2 patients still had dysphagia. In 2 patients, vagal MEPs of one side transiently disappeared when the tumors were dissected from the brainstem or the vagal rootlets. After surgery, both patients had dysphagia, which recovered in 4 weeks. In 7 patients, MEP amplitude was consistent, maintaining more than 50% of the control level throughout the operative procedures. After surgery all 7 patients were neurologically intact with normal swallowing function. Vagal MEP monitoring with transcranial electrical stimulation and endotracheal tube electrode recording was a safe and effective method to provide continuous real-time information on the integrity of both the supranuclear and infranuclear vagal pathway. This method is useful to prevent intraoperative injury of the brainstem corticobulbar tract or the vagal rootlets and to avoid the postoperative dysphagia that is often associated with brainstem or skull base surgeries.

Use of Endotracheal Tube Electrodes in Treating Glossopharyngeal Neuralgia: Technical Note

Background/Aims: This paper describes the use of endotracheal tube surface electrodes to help delineate the sensory and motor vagal rootlets which may be sacrificed during the surgical treatment of glossopharyngeal neuralgia. Methods: Three patients with glossopharyngeal neuralgia were studied. All patients had their procedure under general anesthesia and a nerve integrity monitor electromyography endotracheal tube (Medtronic Xomed, Jacksonville, Fla., USA) was inserted under direct vision by the anesthesiologist. A bipolar stimulating electrode identified which, if any, of the upper rootlets of the vagus nerve caused a motor contraction near the vocal cords (i.e. motor branch) and which did not cause contractions (i.e. sensory branch). Sectioning of the glossopharyngeal and any purely sensory rootlets of the vagus nerve was subsequently performed. Results: All patients had immediate and long-lasting relief of their glossopharyngeal neuralgia. In all 3 patients, use of the bipolar stimulating electrode on the lower vagal rootlets induced a recordable muscle action potential in the region of the vocal cords with low current (<0.2 mA). There were no complications consequent to placement of the nerve integrity monitor endotracheal tube. Conclusion: Due to the ease of use and reduced trauma, compared to needle electrodes, we would advocate endotracheal tube surface electrode monitoring in all patients undergoing surgical treatment of their glossopharyngeal neuralgia or any intracranial procedure where the integrity of the vagal nerve is in jeopardy.

Spontaneous and Evoked Laryngeal Electromyography of the Thyroarytenoid Muscles: A Canine Model for Intraoperative Recurrent Laryngeal Nerve Monitoring

We sought to determine the feasibility of performing spontaneous and evoked intraoperative laryngeal electromyography (L-EMG) using nerve monitoring equipment and to compare recording electrode configurations and methods of recurrent laryngeal nerve (RLN) stimulation in dogs. Four beagles underwent crush injury of the left RLN, and 2 beagles underwent left RLN transection. Serial spontaneous and evoked L-EMG was recorded with the NIM-Response nerve monitoring system under sedation. Transesophageal, percutaneous, and direct open RLN stimulation was performed. Recordings of spontaneous and evoked responses were made with endotracheal tube surface electrodes and bipolar vocal fold needle electrodes. The L-EMG procedures were repeated every 1 to 2 weeks after injury, and intersubject and intertrial differences were evaluated. Low-amplitude motor unit action potentials, polyphasic potentials, fasciculations, and fibrillations were detected in injured animals with bipolar needle recording electrodes with this system of spontaneous L-EMG. The surface recording electrodes did not detect pathologic waveforms. Percutaneous needle stimulation of the RLN is possible at currents slightly higher than those used for direct stimulation. Consistent, discrete, transesophageal stimulation of the RLN could not be reliably performed. Recording evoked responses with needle electrodes generated sharper waveforms, facilitating calculation of latency and wave duration. Evoked L-EMG utilizing surface recording electrodes limited the intertrial and intersubject variability of evoked amplitude. Typical patterns of nerve injury can be detected with this system of intraoperative L-EMG in a canine model. Quantitative measures of amplitude, latency, and wave duration in healthy and injured canine RLNs may be determined with this system.

Serial Electromyography of the Thyroarytenoid Muscles Using the NIM-Response System in a Canine Model of Vocal Fold Paralysis

We sought to determine whether serial intraoperative laryngeal electromyography (L-EMG) or evoked L-EMG predicts vocal fold (VF) recovery following iatrogenic injury. Six beagles were sedated, and bipolar needle electrodes were inserted into each thyroarytenoid (TA) muscle. Endotracheal tube surface electrodes were also placed. As the sedation lightened, L-EMG activity was recorded from all electrodes with an intraoperative nerve monitoring system. The neck was opened, and direct recurrent laryngeal nerve (RLN) stimulation was performed. Subsequently, 4 animals underwent crush injury of the left RLN,and 2 animals underwent nerve transection. The L-EMG procedures were repeated every 1 to 2 weeks until left VF motion was observed in the dogs that suffered RLN crush injury. At each time point, the neck was opened and both RLNs were stimulated. Fibrillation potentials were detected in all animals after RLN injury. A change to electrical silence was seen in the animals in the crush injury group that were evaluated during the week preceding VF recovery. Fibrillation potentials and VF immobility persisted in the transection group throughout the complete time course of these experiments. The first appearance of an evoked response coincided with or occurred after the return of left VF motion in the crush injury group. The threshold, latency, and amplitude differed from those of the controls and approached normal values over time. No response was detected in the transected nerves. The disappearance of fibrillations on intraoperative L-EMG was noted in the animals tested the week before the return of VF motion, and the return of motor unit action potentials was seen along with return of VF function. Evoked L-EMG was not helpful in predicting the return of VF mobility, but it may help quantify degrees of RLN injury and predict the speed of recovery.

Endotracheal tube electrodes to map and monitor activities of the vagus nerve intraoperatively. Technical note.

Difficulty swallowing due to damage of the vagus nerve is one of the most devastating complications of surgery in and around the medulla oblongata; therefore, intraoperative anatomical and functional evaluation of this nerve is crucial. The authors applied endotracheal tube surface electrodes to record electromyography (EMG) activity from vocal cords innervated by the vagus nerve. The vagal nucleus or rootlet was electrically stimulated during surgery and vocalis muscle EMG activities were displayed by auditory and visual signals. This technique was used successfully to identify the vagus motor nerve and evaluate its integrity during surgery. The advantages of this method compared with the use of needle electrodes include safe simple electrode placement and stable recording during surgery. In cases involving a pontine cavernoma pressing the nucleus or a jugular foramen tumor encircling the rootlet, this method would be particularly valuable. Additional studies with a larger number of patients are needed to estimate the significance of this method as a means of functional monitoring to predict clinical function.