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

Abstract

Objectives/Hypothesis 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. Study Design Retrospective review. Methods 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. Results 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. Conclusions 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. Level of Evidence 4 Laryngoscope, 128:2910–2915, 2018

In Response to Letter to the Editor Regarding: Is Cricothyroid Muscle Twitch Predictive of the Integrity of the EBSLN in Thyroid Surgery?

“…2 In the letter, the authors commented that the new electromyography (EMG) endotracheal tube, needle, or surface electrodes using an intraoperative neuromonitoring system (IONM) could objectively and quantitatively evaluate the cricothyroid muscle (CTM). [3][4][5] Moreover, they pointed out that the procedure of EBSLN stimulation and CTM twitch assessment was incomplete in our study. Finally, they suggested that testing CTM twitch is not only a diagnostic tool but also a useful and effective preventive tool for EBSLN injury.…”

“…Three well-designed studies mentioned in their letter were conducted on the new adjunctive devices for IONM system. [3][4][5] In these studies, EBSLNs were intentionally explored and the exposed nerves were stimulated with the probe under direct vision. [3][4][5] However, intentional dissection for visual identification of EBSLN is not established as a standard procedure in thyroidectomy.…”

“…[3][4][5] In these studies, EBSLNs were intentionally explored and the exposed nerves were stimulated with the probe under direct vision. [3][4][5] However, intentional dissection for visual identification of EBSLN is not established as a standard procedure in thyroidectomy. 6 In addition, not every surgeon routinely performs the dissection for visual identification of EBSLN because it may be invasive and harmful to the nerve and to the postoperative voice outcome.…”

Trans–thyroid cartilage recording for neural monitoring of the recurrent laryngeal nerve in thyroid surgery

“…This method can more securely fix the electrodes on the TC and obtain more stable EMG signals. Liddy et al also report similar anterior laryngeal electrodes to reduce monitoring error caused by endotracheal tube displacement …”

“…Liddy et al also report similar anterior laryngeal electrodes to reduce monitoring error caused by endotracheal tube displacement. 13 International IONM guidelines recommend an initial EMG amplitude (V 1 signal) >500 μV. 1,2 This initial high amplitude is essential for the correct interpretation, diagnosis, and verification of a functional intact RLN, for definition of a significant reduction of signal, reentry signal (i.e., subsequent intraoperative EMG signal recovery and normal postoperative vocal cord function), loss of signal, and again for the correct evaluation of the results.…”