Introducing the Trigemino-Vocal Reflex: New insights to assess brainstem connectivity under general anesthesia

This descriptive study aims to provide evidence of a newly described reflex, the Trigemino-Vocal Reflex (TVcR). It confirms the functional connectivity between trigeminal and vagal systems in humans under anesthesia.

We stimulated the mental branch of the trigeminal nerve at the mandibular foramen in 47 patients undergoing different surgeries and recorded vocal cord muscle responses. Stimulation consisted of either a single electrical pulse or a train of 2-4 pulses, based on anesthesia depth. The recording was made by using an adhesive tube electrode.

A bilateral response was observed in 41 patients, while 2 showed only a unilateral response. All 43 exhibited an early potential (R1) with a latency of about 30 ms, and 24 also displayed a late potential (R2) with a latency ofaround 65 ms.

We demonstrate the potential to record the newly described TVcR, recording vagal motor responses in the vocal cords following stimulation of the trigeminal nerve at the mandibular foramen in anesthetized patients.

We introduce a newly described reflex that may be valuable in intraoperative neurophysiological monitoring and could enhance our understanding of brainstem physiology.