Intraoperative Neurophysiological Monitoring for the Vagus Nerve: Case Illustrations

The vagus nerve, cranial nerve 10 (CN X), runs from the medulla into the neck. The relevant bilateral branches of the nerve pertinent to this atlas include the recurrent laryngeal nerve and the superior laryngeal nerve, which further branches into internal and external branches. There is a potential risk for injury to the vagus nerve during head and neck surgeries. The vagus nerve can be monitored by use of an endotracheal tube containing recording electrodes which after intubation lie at the level of the vocal cords for recording the distal recurrent laryngeal nerve (RLN). Needle electrodes are also placed into the cricothyroid muscle for monitoring of the external branch of the superior laryngeal nerve (EBSLN). Please see Chaps. 8 and 9 for monitoring techniques for the RLN and EBSLN. The vagus nerve is directly stimulated by the surgeon in the neck with the use of a Prass monopolar cathode stimulator and reference anode needle electrode placed into the ipsilateral trapezius muscle. Stimulus intensities of 0.5-2 milliamps (mA) are most frequently used. Free running EMG for any indirect stimulation of the vagus nerve recording from the above electrodes in the ETT and cricothyroid muscle is also monitored. All waveforms and data were obtained utilizing Cadwell Cascade® intraoperative monitoring recording equipment.