Background: Adoption of continuous intraoperative neural monitoring (C-IONM) in endoscopic thyroid surgery is limited due to the uneasy application of C-IONM electrode. Feasibility for transcutaneous vagal nerve stimulation was tested. Materials and Methods: Vagus nerve (VN) and recurrent laryngeal nerve (RLN) were mapped and stimulated in different neck sites by (1) transcutaneous monopolar intermitted stimulation; (2) prototype for continuous transcutaneous stimulating electrodes (TSEs), that is, suction ball C-IONM electrode remodeled; (3) stimulation subsequently to neck CO2 insufflation; (4) direct stimulation of surgical exposed nerves. Electromyographic (EMG) parameters were compared. Results: Six anterior neck locations evoked EMG signals of VNs and RLNs. Location Nos. 3 and 6 according to our scheme were over the VNs, confirmed by ultrasonography and subsequent dissection. Other locations did not correspond to nerves sites. Transcutaneous thresholds were higher than surgical exposed ones to produce a consistent and satisfactory EMG response. TSE recorded solely in location No. 5 with amplitude values 256-9 μV. It was not possible to stimulate and monitor the RLN and VN after neck CO2 insufflation. Conclusion: Transcutaneous C-IONM is unfeasible for endoscopic thyroidectomy.
Keywords: continuous neural monitoring; porcine model; recurrent laryngeal nerve; thyroid surgery; transcutaneous electric stimulation.