Safety Analysis Of Continuous Intraoperative Neuromonitoring And Security Application Of Electrotome In The Region Of Recurrent Laryngeal Nerve

Objective:This research developed experimental animal models of recurrent laryngeal nerve protection during thyroid surgery in miniature pigs, to investigate and analyze the safety of continuous intraoperative neuromonitoring (C-IONM) during thyroidectomy; Based on the safety of C-INOM, we further explored the security application of electrotome in the region of recurrent laryngeal nerve under C-IONM monitoring.Materials and methods:1. Experimental instruments: NIM-Response(?) 3.0TM nerve monitor (Medtronic, USA),reinforced EMG the endotracheal tube (Medtronic, USA), the APS electrode, Valleylab electrotom(Force FX-8C).2. The experimental model: experimental miniature pigs (provided by Military Medical Science Academy), the pigs were anesthetized with intravenous thiopental (15mg/), then a nerve integrity monitor endotracheal tube was inserted, and general anesthesia was maintained with sevoflurance (1-2%). According to the standardized procedure for C-IONM, the vagus nerve (VN) and recurrent laryngeal nerve (RLN) were identified and APS electrode was positioned on VN.3. Safety analysis of C-IONM: 20 pigs were randomly divided into experimental group and blank control group (10 per group), and then randomly selected 5 right and 5 left VN from each group. Vagus nerve in experimental group was stimulated continuously with a 3mA electric current for 3 hours after APS electrode location, while without any stimulation in control group. The index, including blood pressure, heart rate, blood oxygen saturation and amplitude and latency of electromyography (EMG), was monitored and recorded in series per 15 minutes until to the end of the experiment after3 hours. The vagus nerve tissues by stimulating and ipsilateral RLN tissues were taken to make paraffin sections for nerve damage assessment.4. Security application of electrotome under C-IONM monitoring: Right RLNs of 21 pigs were classified equally into 3 groups according to the distance between electrotome application and the RLN: Group 1 (1mm), Group 2 (2mm), Group 3 (3mm). The application time of electro tome was set to be 3 s and the energy of electro tome was set at 90w. The application site was selected between the 2nd and 3rd tracheal cartilages. The amplitude and latency waveforms were displayed separately, and an upper limit threshold for the latency (+10%) and lower limit threshold for amplitude (-50%) were set as surgery alarm threshold. The amplitude and latency of EMG were observed and compared before and after damage. Meanwhile, recording the amplitude and latency of EMG at the time of 15min, 30min, 60min after the electrotome application to observe neural functional recovery. The injury nerve tissues and the left normal nerve tissues were taken to make pathological sections and observed under microscope to evaluation of nerve injury.Results:1. The average operation time of dissecting carotid sheath and APS electrode location after the exposure of vagus nerve was (19.70±3.57) min. There was no injury of blood vessel and vagus nerve caused by dissecting carotid sheath, and there was no loss of signal (LOS) during the whole experiment, either.2. Safety analysis of C-IONM application: There was no significant difference between the experimental group and control group in physiological index (P>0.05). In experimental group, the physiological index and EMG recorded from initial and 3 hours after the stimulation were compared, but the difference had no significance (P>0.05).Histological analysis showed that the nerve tissues after APS stimulation had no obvious damage.3. The security application of electrotome under C-IONM monitoring: The change of EMG amplitude and latency before and after injury of elecctrotome had significant difference in both Group 1 and Group 2 (P>O.05), and EMG did not recover to normal till the end. In Group 3, after injury of electrotome, the amplitude decreased less than 50%and the latency extended less than 10%, so no alarm was caused by the change. The changed EMG signal could recover in 15 minutes, and the change of EMG had no obvious difference (P>0.05). Under microscopic observation, nerve tissues in Group 1 had obvious damage; nerve tissues in Group 2 had edema of nerve bundle; nerve tissues in Group 3 and the blank control group appeared normal neural structure.Conclusion:1. Following the standardized steps of C-IONM, dissecting the carotid sheath and locating APS electrode will not cause mechanical damage of the vagus nerve and blood vessel.2. The constant stimulation by APS electrode located on vagus nerve has no significant effect on physiological function and nerve function, so the application of C-IONM is safe and reliable.3. During thyroid surgery, the safe distance between electrotome and nerve should not less than 3 mm in the region of recurrent laryngeal nerve.