Periodic vagus nerve stimulation for continuous intra operative recurrent laryngeal nerve monitoring

Abstract

The recurrent laryngeal nerve (RLN) is at risk of injury in multiple operations in the skull base, neck and thoracic regions. Nerve monitoring has been employed for more than 3 decades, aiming to aid the surgeon to identify the RLN and reduce the risk of RLN injury. Conventional nerve monitoring requires identification and active intermittent stimulation of the RLN. Between intervals of stimulation, nerve injuries can still occur without the surgeon recognizing it. A new system of continuous intraoperative nerve monitoring (CIONM) works through automatic periodic stimulation (APS) of the vagus nerve has been developed. The new system employs an electrode that is attached to the vagus nerve at the start of the operation. Patient will be intubated with an endotracheal tube with contact electrodes on the vocal cords for monitoring the EMG of the vocalis muscles similar to conventional RLN monitoring. The nerve monitor will provide periodic stimulation of the vagus nerve and the integrity of the RLN can be assessed by the amplitude of the latency of EMG. Reduction in the amplitude and increase in latency signal imminent RLN injury. The system is designed for thyroid operations but we have adopted the system for minimally invasive oesophagectomy. Initial experience with 10 patients, the time required for placement of the vagus nerve electrode averaged 35 min (24-80 min). There were two adverse events. In one event, there was more than 50% reduction of EMG amplitude that persisted but the patient had no vocal cord paralysis after operation. In another patient the EMG reduced by 75% and persisted. The patient had temporary vocal cord paralysis recovered 6 weeks after operation. CIONM may reduce the incidence of RLN injury by alerting the surgeon imminent nerve injury.