Technique a 'Huge Breakthrough' for Spine, Thyroid Surgery

Deborah Brauser

July 10, 2017

A novel, "less invasive" technique can help clinicians to continuously assess laryngeal and vagus nerve function while patients are under general anesthesia during neurosurgery or otolaryngology procedures, new research suggests.

Although postsurgery nerve injuries reportedly affect about 10% of patients, the most common process has been to monitor these nerves only intermittently by stimulating them at various times throughout a procedure.

The new technique uses a simple endotracheal tube, which then simultaneously and continuously stimulates and monitors nerve responses.

Results from a case series of 15 patients in whom the new technique was used during thyroidectomy or cervical spine fusion, show there were no complications or procedure-related adverse events for any of the participants.

"We were able to find a reflex in the human voice box that has been thought not to exist under anesthesia in humans," lead author, Catherine F. Sinclair, MD, Department of Otolaryngology Head and Neck Surgery at Mount Sinai West Hospital, New York City, told Medscape Medical News.

"Never before have we been able to monitor both sensory and motor branches of the vagus nerve," Dr Sinclair added in a press release. This ability "is a huge breakthrough and will hopefully translate into improved patient outcomes."

The study was published in the July issue of Clinical Neurophysiology.

A Better System

Injuries after thyroid or anterior cervical spine surgeries have included vocal paralysis or swallowing dysfunction.

Although continuous stimulation could help predict potential damage before it occurs, thereby allowing clinicians to take preventive measures, the only method until now has required "putting probes around the nerves, which is quite invasive and can lead to nerve injury itself," said Dr Sinclair.

Instead, she created a new and "better" system with coinvestigators Maria J. Tellez, MD, and Sedat Ulkatan, MD, both also from Mount Sinai West Hospital.

"This is a non-invasive method for monitoring laryngeal nerve and vocal fold function that has been simplified to a placement of just one endotracheal tube," Dr Ulkatan said in the release. Tube-based surface electrodes then elicit a laryngeal adductor reflex (LAR).

In addition, "contralateral R1 (cR1) and R2 (cR2) responses were recorded using the endotracheal tube electrode contralateral to the simulating electrode," write the investigators.  

Dr Sinclair noted that they also did not use gas anesthesia. "Instead, we used an anesthetic method called 'total intravenous anesthesia.' And when we give this, not only is the voice box reflex present, it's very robust and reliable."

The 15 participants in the new case report were aged 28 to 84 years (mean age, 55 years), and 12 were women.

After the patients were intubated with an endotracheal tube with imbedded surface electrodes, which have contact with the right and left vocal folds, videolaryngoscopy was used to recheck and adjust tube position as needed.

100% LAR Response

Results showed 100% LAR elicitation for the entirety of all procedures, as well as a reliable cR1 response.

The mean onset latency of cR1 response was 22.4 milliseconds for the right vocal fold and 22.2 milliseconds for the left vocal fold. The mean amplitudes were 243.4 µV and 222.7 µV, respectively.

Ten patients (66.7%) also had a cR2 response, with mean onset latency of 61.1 milliseconds and 59.9 milliseconds, respectively.

There were no reports of total reflex loss during the procedures and no reports of vocal cord paralysis afterward.

"The LAR monitors the entire vagus nerve reflex arc and is thus applicable to all surgeries where vagal nerve integrity may be compromised," write the investigators, reiterating the  advantages of simplicity and continuous monitoring.

"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 Dr Ulkatan.

"This novel methodology will provide neurosurgeons important feedback to protect [the] structures, reducing life-threatening surgical complications."

Used in 100 Patients

Dr Sinclair noted that she and her colleagues have now used this process in more than 100 patients.

"This still isn't a lot in the whole scheme of things, and there are still a whole lot of technical things we need to learn about the reflex. But from what we've seen, it seems to be a very reliable way of monitoring this vagal nerve pathway," she said.

"The beauty of it is it doesn't rely on any external equipment, just on a breathing tube that is already widely used not only in head and neck surgery but also in neurosurgery. And I think we can recommend this [process] to other clinicians as a promising new technique."

In fact, she reported that "people are also starting to use it overseas on an experimental basis, and it seems to be giving them good results."

The investigators have disclosed no relevant financial relationships.

Clin Neurophysiol. 2017;128:1399-1405. Full text

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