Comparison of Recording Electrode Arrays in Endotracheal Thyroid Monitoring Tubes in a Porcine Model.

OBJECTIVES: Alteration in positioning or head manipulation during thyroid surgery can lead to endotracheal tube movement and potentially a change in intraoperative neural monitoring readings. We sought to study the impact of positional changes on two different commercially available recording electrode arrays. MATERIALS: Eight pigs divided equally into two study groups based on recording electrode arrays were used: Neurosign Lantern Laryngeal Electrode (LLE) (Neurosign_Technomed, The Netherlands) and Medtronic NIM EMG [neural integrity monitor electromyogram] endotracheal tube (ETT) (Medtronic, Jacksonville, FL). Neck movement and reposition were performed for all pigs. Signal data, including amplitude and latency, were collected for vagus nerve, recurrent laryngeal nerve (RLN), and external branch of superior laryngeal nerve (EBSLN) before and after repositioning. The differences of amplitude and latency by pre- and post-repositioning were compared for all animals. RESULTS: Eight pigs were included in the current study. ETT group (Medtronic) had a significant decrease in amplitude of all tested nerves: for the vagus nerve on the left side by 36.30% (P = .021) and on the right by 49.29% (P = .024), for RLN on the left by 30.22% (P = .014) and on the right by 42.34% (P = .004), and for EBSLN on the left by 63.62% (P = .003) and on the right by 13.58% (P = .010). The amplitude changes in LLE group (Neurosign) repositioning were not statistically significant in all nerves. CONCLUSION: Recording electrode array configuration can impact the stability of nerve monitoring signal during thyroid surgeries. Repositioning was associated with changes in nerve signal amplitude in ETT group (Medtronic), whereas LLE (Neurosign) did not show any significant differences. Human studies are warranted. LEVEL OF EVIDENCE: NA Laryngoscope, 130:2499-2505, 2020.

Intraoperative Neuromonitoring During Thyroid Surgery: The Effect of Surgical Positioning.

Intraoperative neuromonitoring during thyroid surgery has been used to successfully prevent permanent neurological injury by early identification of anatomical variants. Proper interpretation of neuromonitoring data requires knowledge of what factors might affect the data. In this study, we examined the effect of surgical positioning on the latency and amplitude of neural recordings made from the vocalis muscle during thyroid surgery. A retrospective review was performed of 145 patients who underwent thyroid surgery. Eighty-three had open cervical procedures, and 62 had robotic-assisted transaxillary procedures. Intraoperative neuromonitoring recordings were made by stimulation of the vagus and recurrent laryngeal nerves for both groups. Ultrasound measurements were made of a subset of the transaxillary patients immediately before and after arm positioning. Groups differed only on right-sided recordings. Patients with transaxillary surgeries had significantly shorter latencies evoked from the vagus nerve. We found that vagus nerve-evoked latencies were also correlated to ultrasound measurements of the nerves. Surgical positioning during thyroid surgery is a factor that may affect intraoperative neuromonitoring data and should be taken into account by the surgeon during interpretation.

Electrophysiological identification of nonrecurrent laryngeal nerves.

OBJECTIVES/HYPOTHESIS: The nonrecurrent laryngeal nerve (NRLN) is a common anatomic variation of the right recurrent laryngeal nerve (RLN), which has been associated with an increased risk of injury during thyroid and parathyroid surgery. We suggest that early successful identification using intraoperative nerve monitoring (IONM) and preservation of this variant will help the surgeon to avoid injury to this nerve. Our objective was to examine the electrophysiological parameters of the NRLN and the efficacy of IONM for successful identification of the NRLN. STUDY DESIGN: Retrospective database analysis. METHODS: This is a retrospective study of a prospectively collected database of all patients who underwent thyroid and parathyroid surgeries by a single surgeon at a tertiary care center over 3 years (n = 481). Patients' demographic data and operative reports, including the IONM reports, were reviewed. Average stimulation thresholds with resulting amplitudes and latencies were compared. Preoperative and postoperative laryngoscopy were performed in all cases. RESULTS: We identified 15 NRLNs (2.2%) in a total 682 laryngeal nerves. No left-sided NRLNs were observed. The average right vagus latency in the NRLN group was shorter than that of the RLN group (2.40 ms ± 0.49 ms vs. 3.43 ms ± 1.03 ms; P < .001). No statistically significant difference was observed between the initial amplitudes of the right vagus nerves in the two groups (713.67 µV ± 208.71 µV vs. 816.22 µV ± 470.45 µV; P = .14). All NRLN cases exhibited normal functioning of vocal cords on postoperative laryngoscopy. CONCLUSIONS: IONM is highly effective in the identification of the NRLN. Right vagus nerve latency in the NRLN group was found to be significantly shorter than in the RLN group. Early identification of the NRLN allowed cautious preservation of the NRLN, resulting in excellent postoperative outcomes. The rate of NRLN identification may be improved by routine use of IONM. LEVEL OF EVIDENCE: 4 Laryngoscope, 127:2189-2193, 2017.