Evaluating The Safety Of The Harmonic Scalpel Around The Recurrent Laryngeal Nerve

Background: The Harmonic Scalpel (HS) is widely used in thyroidectomy. Determining the safety margin of using the HS near the recurrent laryngeal nerve (RLN) is helpful in preventing the injury to this nerve during thyroidectomy.Methods: The parameters of evoked electromyography (EEMG) of vocal muscles before and after using the HS at a power level of 3 were recorded in a rabbit model. Masson staining was used to determine lateral injury caused by incisions using the HS.Results: After the activated tip of the HS made contact with the RLN for >= 1 s or was placed 1 mm from the nerve for 3 or 5 s or 2 mm from the nerve for 5 s, significant changes were observed in the minimal stimulus current intensity threshold, the optimal stimulus current intensity threshold, the onset latency and the wave amplitude of EEMG. After the activated HS tip touched the RLN or was placed 1 mm to the nerve for >= 1 s or 2 mm to the nerve for 5 s, significant changes were found in peak latency. The thickness of injured lateral tissue was <1, 1- 2 and >2 mm when using HS for 1, 3 and 5 s, respectively.Conclusion: When used near the RLN at a power level of 3, the activated HS tip should be >= 2 mm from the nerve and the duration of incision should be <= 3 s.