Intraoperative Neuromonitoring During Thyroid Surgery: The Effect of Surgical Positioning

Abstract

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.

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

“…16,21 Our previous study showed a significant decrease in right RLN amplitude with a TAA compared to a TCA. 15 However, in our current study, with a larger study population, there was no difference in RLN amplitude between approaches. Furthermore, a TAA was not associated with decreased amplitude or increased latency of the vagus nerve on either side, even though there was a statistically significant change in vagus nerve location post-positioning bilaterally.…”

“…The aim of this study was to build upon our previous study to help define expected IONM measurements during transaxillary thyroid and parathyroid surgery. 15 In both our previous and current studies, mean evoked latency of the right vagus nerve was significantly decreased in TAA procedures. In our current study, this difference was also observed when analyzing total thyroidectomy and right hemithyroidectomy separately.…”

“…As described in our previous study, this may be due to the different anatomical course between the right and left RLN. 15 Abduction and external rotation of the right shoulder during tranaxillary surgery elevate the clavicle and the subclavian artery, which reduces inferior tension placed on the right vagus nerve by the RLN looping around the subclavian artery. 18 Conversely, the inferior anchor point of the left vagus nerve by the aortic arch is relatively fixed.…”

“…Consistent with our previous study, the distance of the vagus nerve from the trachea was measured with intraoperative ultrasound using a 15-MHz linear transducer immediately before and after patient positioning for a TAA. 15 An experienced neurophysiologist performed IONM using the Cadwell Cascade IONM system (Cadwell Corporation, Kennewick, WA) (Figure 1). To ensure the proper placement of electrodes between the vocal folds, an endotracheal tube with lantern-style adhesive electrodes (Neurovision Medical, Ventura, CA) was placed using video laryngoscopy.…”

“…In our previous study, we showed that patient positioning affects IONM electromyography data. 15 In the current study, we aimed to further analyze IONM between transcervical and transaxillary approaches by pooling more data. The authors postulated that the current study would support our previous findings.…”