P14-F Intraoperative-neuromonitoring (IONM) of the vagal circuit through the laryngeal-adductor-reflex (LAR) to assess the lower-brainstem’s integrity

Abstract

Background Brainstem surgeries represent a challenge due to the high concentration of nuclei and pathways in a small space. We present 2 cases in which the vagus nerve and lower brainstem’s integrity were assessed by IONM of the laryngeal-adductor-reflex (LAR). Methods Case-1: A 62-year-old woman who underwent resection of a large left-Vestibular-Schwannoma. Case-2: A 32-year-old man scheduled for resection of a right-sided-CPA-meningioma. IONM technique consisted in the monitoring of corticobulbar, motor, somatosensory and brainstem-auditory evoked-potentials, blink-reflex, LAR and cranial nerve mapping. LAR was evoked by applying a single electrical stimulus on the laryngeal mucosa using surface-electrodes attached to the endotracheal-tube (EET), recording the R1/R2 responses contralateral to the stimulus and ipsilateral to the surgical field from electrodes contained in the EET. Results In both cases, all responses (but BAEP on the first patient) were elicited bilaterally at the onset of surgery. On two occasions in both patients during the resection of the tumor adjacent to X cranial-nerve, a significant drop in blood-pressure and heart-rate was observed. The surgeon was informed immediately, and surgical manipulation was interrupted. Concomitantly LAR amplitude dropped with improvement when hemodynamic parameters returned to normal. At one time, LAR responses decreasing preceded BP and HR dropping enable us to warn the surgeon. We believe that the vagus’ surgical stimulation was the cause of these depressant responses. Conclusions LAR is a method that continuously monitors the afferent-efferent-pathways of the vagal-circuit, optimizing the IONM during posterior-fossa surgeries where the integrity of the brainstem and X c.n. could be endangered.