New Technique Monitors Nerves During Surgery

A novel intraoperative technique takes advantage of the laryngeal adductor reflex (LAR) to monitor the laryngeal and vagus nerves in patients under general anesthesia.

Developed at Mount Sinai West Hospital (New York, NY, USA), the method is based on an endotracheal tube with electrodes placed along its side. Electrodes along one side of the endotracheal tube are used to electrically stimulate the brain stem via the superior laryngeal nerve, while the electrodes along the other side are used to record LAR responses in vocal fold mucosa. The technique allows surgeons to monitor nerve function and change their approach to prevent post-surgical voice and swallowing complications resulting from nerve dysfunction.

In a case series of 15 patients undergoing thyroid and cervical spine surgeries under total intravenous general anesthesia, the researchers found that they could make immediate surgical modifications and adjustments during the procedures to prevent irreversible nerve damage, with all 15 cases resulting in improved patient outcomes and lower complication rates. The researchers added that as LAR monitors the entire vagus nerve reflex arc, it is applicable to all surgeries where vagal nerve integrity may be compromised. The study was published in the July 2017 issue of Clinical Neurophysiology.

“This simple technique will likely have wide-reaching effects by greatly enhancing our ability to monitor the vagus nerve in the head and neck during neurosurgical and cardiothoracic surgeries,” said lead author otolaryngologist Catherine Sinclair, MD, of Mount Sinai. "Never before have we been able to monitor both sensory and motor branches of the vagus nerve. The ability to monitor sensory function for the first time is a huge breakthrough and will hopefully translate into improved patient outcomes.”

“Surgery of the lower brain stem is still relatively conservative, given the critical functional role of this small area and the lack of reliable techniques to monitor these structures,” said study co-author Sedat Ulkatan, MD, director of intraoperative neurophysiology at Mount Sinai West. “This novel methodology will provide neurosurgeons important feedback to protect vagus nerve and lower brainstem structures, reducing life-threatening surgical complications."

The vagus nerve is the tenth cranial nerve, and interfaces with parasympathetic control of the heart, lungs, and digestive tract. It is the longest nerve of the autonomic nervous system, supplying motor parasympathetic fibers to all the organs (except the adrenal glands), from the neck down to the second segment of the transverse colon. It also innervates several skeletal muscles, including the cricothyroid, the superior, middle and inferior pharyngeal constrictors, and other muscles of the pharynx and larynx, thus controlling muscle movements in the mouth and speech.

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