S124. Comprehensive tube-based methodology for evaluating the brainstem laryngeal adductor reflex in humans under anesthesia

Abstract

The laryngeal adductor reflex (LAR) is a vago-vagal reflex necessary for airway protection that is organized by the brainstem. It consists of an early R1 and late R2 responses that prevent aspiration by causing thyroarytenoid and lateral cricoarytenoid muscles contraction and thus vocal fold closure. The afferent sensation from the glottis and supraglottis mucosa travels through the internal branch of the superior laryngeal nerve (a branch of the vagus nerve) to the nucleus of the solitary tract. The motor neurons contributing to the efferent arc, through the vagus nerve, lie in the nucleus ambiguous. Bilateral simultaneous adduction of both vocal folds is a mandatory condition for achieving an effective protective function of the lower airway. LAR impairment leads to increased risk of aspiration what is highly correlated with increased morbidity and mortality. The LAR was elicited by electrical stimulation of the laryngeal mucosa on the side contralateral to the operative field using the electrodes attached to the endotracheal tube (EET). A single stimulus at intensity up to 15 mA applied. Surface electrodes ipsilateral to the operative field attached to the EET were used to record the contralateral R1 (cR1) and R2(cR2) responses of the LAR. One hundred patients (134 nerves at risk), aged between 21 and 84 years, who underwent thyroid surgeries (19 males, 81 females) were included. Before the surgical procedure started cR1 and cR2 responses were reliably elicited in 100% and 67% of the patients, respectively. Mean cR1 latencies ± standard deviation were 21.6 ± 3 ms (left) and 21.8 ± 2.8 ms (right). Mean cR1 amplitudes were 312.9 ± 178.2 μV (left) and 314 ± 183.7 μV (right). During surgery, monitorability of the LAR decreased to 84% due to methodological limitations. The LAR is a comprehensive tube-based methodology for evaluating the integrity of vagus nerve and brainstem LAR pathway. Advantages over current monitoring techniques including simplicity, ability to continuously monitor neural function without placement of additional neural probes and ability to assess the integrity of both sensory and motor pathways. The LAR has the potential to revolutionize how the vagus nerve is continuously monitored during neck neurosurgical procedures.