The Effect of Patient Positioning on Intraoperative Neuromonitoring During Thyroid and Parathyroid Surgery

Background Intraoperative neuromonitoring (IONM) has been accepted as a routine adjunct among surgeons who perform thyroid and parathyroid surgeries. Thyroid and parathyroid surgeries use various patient positioning strategies that have poorly understood effects on IONM. The aim of this study was to compare IONM signals between the transaxillary and transcervical approaches. Methods In this retrospective cohort study, we evaluated 463 adult patients who underwent a total of 502 procedures. The procedures performed included total thyroidectomy, right or left hemithyroidectomy, and parathyroidectomy. Vagus nerve and recurrent laryngeal nerve (RLN) latency and amplitude measurements were analyzed intra-operatively. The distances between the vagus nerve and the trachea were measured via ultrasound during transaxillary procedures. Results Compared to the transcervical approach, the right vagus nerve latency was significantly decreased in the transaxillary approach. Transaxillary surgery was not associated with increased latency or decreased amplitude on IONM. The distance between the vagus nerve and trachea was significantly decreased post-positioning during transaxillary approaches. Discussion Despite differences in patient positioning, a transaxillary approach was not associated with increased stress on the vagus nerve or RLN, according to IONM data. The decreased right vagus nerve latency associated with a transaxillary approach highlights the importance of considering patient positioning and laterality while interpreting IONM data.

Prognostic Indicators of Non-Transection Nerve Injury and Vocal Fold Motion Impairment After Thyroid Surgery – Correlation Between Intraoperative Neuromonitoring Findings and Perioperative Voice Parameters

ObjectivesIn patients with recurrent laryngeal nerve (RLN) injury after thyroid surgery, unrecovered vocal fold motion (VFM) and subjective voice impairment cause extreme distress. For surgeons, treating these poor outcomes is extremely challenging. To enable early treatment of VFM impairment, this study evaluated prognostic indicators of non-transection RLN injury and VFM impairment after thyroid surgery and evaluated correlations between intraoperative neuromonitoring (IONM) findings and perioperative voice parameters.Methods82 adult patients had postoperative VFM impairment after thyroidectomy were enrolled. Demographic characteristics, RLN electromyography (EMG), and RLN injury mechanism were compared. Multi-dimensional voice program, voice range profile and Index of voice and swallowing handicap of thyroidectomy (IVST) were administered during I-preoperative; II-immediate, III-short-term and IV-long-term postoperative periods. The patients were divided into R/U Group according to the VFM was recovered/unrecovered 3 months after surgery. The patients in U Group were divided into U1/U2 Group according to total IVST score change was <4 and ≥4 during period-IV.ResultsCompared to R Group (42 patients), U Group (38 patients) had significantly more patients with EMG >90% decrease in the injured RLN (p<0.001) and thermal injury as the RLN injury mechanism (p=0.002). Voice parameter impairments were more severe in U Group compared to R Group. Compared to U1 group (19 patients), U2 Group (19 patients) had a significantly larger proportion of patients with EMG decrease >90% in the injured RLN (p=0.022) and thermal injury as the RLN injury mechanism (p=0.017). A large pitch range decrease in period-II was a prognostic indicator of a moderate/severe long-term postoperative subjective voice impairment.ConclusionThis study is the first to evaluate correlations between IONM findings and voice outcomes in patients with VFM impairment after thyroid surgery. Thyroid surgeons should make every effort to avoid severe type RLN injury (e.g., thermal injury or injury causing EMG decrease >90%), which raises the risk of unrecovered VFM and moderate/severe long-term postoperative subjective voice impairment. Using objective voice parameters (e.g., pitch range) as prognostic indicators not only enables surgeons to earlier identify patients with low voice satisfaction after surgery, and also enable implementation of interventions sufficiently early to maintain quality of life.