Effect of superior laryngeal nerve block in alleviating sore throat after application of i-gel supraglottic airway: a randomized controlled trial.

BACKGROUND: Postoperative sore throat (POST) is a common complaint after supraglottic airway device (SAD) application. Internal branch of the superior laryngeal nerve (iSLN) block has the potential to alleviate POST. The aim of this trial was to explore the effect of iSLN block in alleviating sore throat, as well as to identify the potential risk factors for POST after SAD insertion. METHODS: One hundred thirty-four patients scheduled for elective gynecological surgery were randomized to either group T: tetracaine syrup (1%) for local lubrication on i-gel supraglottic device (n = 67) or group B: i-gel insertion with water based lubricant on it and followed by bilateral iSLN block (ropivacaine, 0.375%, 2 ml for each side) (n = 67). Under ultrasound guidance, iSLN was exposed below thyrohyoid membrane. The primary outcome was the intensity of sore throat at 6 h after surgery. In addition, POST score at 0.5 h and 24 h, the severity of postoperative swallowing discomfort, acoustic analysis and complications were measured. RESULTS: Compared with tetracaine syrup for local lubrication, iSLN block resulted in a reduced intensity of POST at 0.5 h (P = 0.044, OR = 1.99, 95%CI 1.02 to 3.88) and 6 h (P < 0.001, OR = 5.07, 95%CI 2.53 to 10.14) after surgery, as well as less severity of swallowing discomfort (P < 0.001, OR = 2.21, 95%CI 1.63 to 2.99) and cough (P = 0.039, OR = 1.97, 95%CI 1.04 to 3.73). The patients after iSLN block presented lower jitter and shimmer value in acoustic analysis at 6 h after surgery (P < 0.001). CONCLUSIONS: iSLN block was effective in alleviating POST, improving voice function, as well as reducing postoperative swallowing discomfort and coughing. TRIAL REGISTRATION: Chinese Clinical Trial Registry (ChiCTR2000037974) on 8th Sept 2020.

Ultrasound-guided internal branch of superior laryngeal nerve block on postoperative sore throat: A randomized controlled trial.

INTRODUCTION: Ultrasound-guided internal branch of the upper laryngeal nerve block (USG-guided iSLN block) have been used to decrease the perioperative stress response of intubation. It is more likely to be successful than blindly administered superior laryngeal nerve blocks with fewer complications. Here, we evaluated the efficacy of USG-guided iSLN block to treat postoperative sore throat (postoperative sore throat, POST) after extubation. METHODS: 100 patients, aged from 18 to 60 years old, ASA I~II who underwent general anesthesia and suffered from the moderate to severe postoperative sore throat after extubation were randomized into two groups(50 cases per group). Patients in group S received USG-guided iSLN block bilaterally (60mg of 2% lidocaine, 1.5ml each side), whereas those in group I received inhalation with 100 mg of 2% lidocaine and 1mg of budesonide suspension diluted with normal saline (oxygen flow 8 L /min, inhalation for 15 minutes). The primary outcome were VAS scores in both groups before treatment (T0), 10 min (T1), 30 min(T2), 1h(T3), 2 h(T4), 4h(T5), 8h(T6), 24h(T7), and 48h(T8) after treatment. The secondary outcome were satisfaction scores after treatment, MAP, HR, and SPO2 fromT0 to T8. The adverse reactions such as postoperative chocking or aspiration, cough, hoarseness, dyspnea were also observed in both groups. RESULTS: Patients in group S had significantly lower VAS score than that in group I at points of T1 ~ T6 (P < 0.01). HR of group S was lower than that of group I at points of T1 ~ T2and T4 (P < 0.05), and MAP was lower than that of group I at points of T1 ~ T3 (P < 0.05). Satisfaction scores of group S were higher than that of group I (P <0.05), In group S, 2 case (4%) needed to intravenous Flurbiprofen Injection 50 mg to relieve pain; in group I, 13 cases (26%) received Flurbiprofen Injection. 2 case of group S appeared throat numbness after treatment for 3 hours; 2 patients have difficult in expectoration after treatment recovered after 3hour. No serious adverse events were observed in both groups. CONCLUSION: Compared with inhalation, USG-guided iSLN block may effectively relieve the postoperative sore throat after extubation under general anesthesia and provided an ideal treatment for POST in clinical work.

Involvement of capsaicin-sensitive nerves in the initiation of swallowing evoked by carbonated water in anesthetized rats.

Capsaicin powerfully evokes the swallowing reflex and is a known therapeutic agent for improving dysphagia and preventing aspiration pneumonia. However, the role of capsaicin-sensitive nerves in the initiation of swallowing evoked by various natural stimuli remains unclear. To explore this question, we blocked laryngeal capsaicin-sensitive nerves following the coapplication of QX-314 and capsaicin (QX/Cap), and investigated the effects on swallowing evoked by mechanical and chemical stimulation in anesthetized rats. Swallows were evoked by capsaicin, carbonated water (CW), distilled water (DW), and punctate mechanical stimulation using von Frey filaments applied topically to the larynx. Swallows were documented by recording electromyographic activation of the suprahyoid and thyrohyoid muscles. The initiation of swallowing by capsaicin was strongly suppressed at 5 min following QX/Cap treatment and returned in a time-dependent manner. CW-evoked swallows at 5 min following QX/Cap treatment were significantly diminished compared with before and 30 min after treatment. In contrast, DW-evoked and mechanically evoked swallows were unchanged by QX/Cap treatment. Furthermore, CW-evoked swallows were virtually abolished by transection of the superior laryngeal nerves and significantly decreased by the topical application of acid-sensing ion channel-3 (ASIC3) inhibitor APETx2, but they were not affected by the nonselective transient receptor potential channel inhibitor ruthenium red or the ASIC1 inhibitor mambalgin-1. Taken together, we speculate that capsaicin-sensitive nerves play an important role in the initiation of CW-evoked swallows.NEW & NOTEWORTHY The initiation of swallowing evoked by laryngeal capsaicin and carbonated water application was diminished by the coapplication of QX-314 and capsaicin. Carbonated water-evoked swallows were also abolished by transection of the superior laryngeal nerves and were inhibited by the acid-sensing ion channel-3 inhibitor. Capsaicin-sensitive nerves are involved in the initiation of carbonated water-evoked swallows.

Liquiritin apioside attenuates laryngeal chemoreflex but not mechanoreflex in rat pups.

Liquiritin apioside (LA), a main flavonoid component of licorice, reportedly suppresses cough responses to inhalation of aerosolized capsaicin [CAP; a stimulant to transient receptor potential vanilloid 1 (TRPV1)] in conscious guinea pigs via acting on peripheral nerves. However, the evidence of LA having a direct effect on airway sensory fibers is lacking. Considering the important role laryngeal chemoreceptors and mechanoreceptors play in triggering apnea and cough, we studied whether LA suppressed the apneic responses to stimulation of these receptors via directly acting on the superior laryngeal nerve (SLN). Intralaryngeal delivery of chemical [CAP, HCl, and distilled water (DW)] and mechanical [an air-pulse (AP)] stimulations was applied in anesthetized rat pups to evoke the apnea. These stimuli were repeated after intralaryngeal LA treatment or peri-SLN LA treatment to determine the direct effect of LA on the SLN. Our results showed that all stimuli triggered an immediate apnea. Intralaryngeal LA treatment significantly attenuated the apneic response to chemical but not mechanical stimulations. The same attenuation was observed after peri-SLN LA treatment. Owing that TRPV1 receptors of laryngeal C fibers are responsible for the CAP-triggered apneas, the LA impact on the activity of laryngeal C neurons retrogradely traced by DiI was subsequently studied using a patch-clamp approach. LA pretreatment significantly altered the electrophysiological kinetics of CAP-induced currents in laryngeal C neurons by reducing their amplitudes, increasing the rise times, and prolonging the decay times. In conclusion, our results, for the first time, reveal that LA suppresses the laryngeal chemoreceptor-mediated apnea by directly acting on the SLN (TRPV1 receptors of laryngeal C fibers).

Dental pulp-derived stem cell conditioned medium to regenerate peripheral nerves in a novel animal model of dysphagia.

In nerve regeneration studies, various animal models are used to assess nerve regeneration. However, because of the difficulties in functional nerve assessment, a visceral nerve injury model is yet to be established. The superior laryngeal nerve (SLN) plays an essential role in swallowing. Although a treatment for SLN injury following trauma and surgery is desirable, no such treatment is reported in the literature. We recently reported that stem cells derived from human exfoliated deciduous teeth (SHED) have a therapeutic effect on various tissues via macrophage polarization. Here, we established a novel animal model of SLN injury. Our model was characterized as having weight loss and drinking behavior changes. In addition, the SLN lesion caused a delay in the onset of the swallowing reflex and gain of laryngeal residue in the pharynx. Systemic administration of SHED-conditioned media (SHED-CM) promoted functional recovery of the SLN and significantly promoted axonal regeneration by converting of macrophages to the anti-inflammatory M2 phenotype. In addition, SHED-CM enhanced new blood vessel formation at the injury site. Our data suggest that the administration of SHED-CM may provide therapeutic benefits for SLN injury.

Isolation of novel biflavonoids from Cardiocrinum giganteum seeds and characterization of their antitussive activities.

ETHNOPHARMACOLOGICAL RELEVANCE: Seeds of Cardiocrinum giganteum var. yunnanense (Leichtlin ex Elwes) Stearn (Liliaceae), also known as Doulingzi, have been used as a folk substitute for conventional antitussive herb "Madouling" (Aristolochia species) to treat chronic bronchitis and pertussis. The active antitussive phytochemicals in C. giganteum seeds are not known. AIM OF THE STUDY: The present work aims at isolating the active phytochemicals in C. giganteum seeds and confirming their antitussive effects. MATERIALS AND METHODS: Active chemicals were isolated from C. giganteum seeds ethanol extract and identified their structures. Antitussive effects were evaluated with the cough frequency of guinea pigs exposed to citric acid. Electrical stimulation of the superior laryngeal nerve in guinea pigs was performed to differentiate the acting site of potential antitussives. RESULTS: Two racemic biflavonoids (CGY-1 and CGY-2) were isolated from C. giganteum seeds. CGY-1 was identified as (S)-2″R,3″R- and (R)-2″S,3″S-dihydro-3″-hydroxyamentoflavone-7- methyl ether, which are new compounds and firstly isolated from C. giganteum seeds. Racemic CGY-2 was identified as (S)-2″R,3″R- and (R)-2″S,3″S-dihydro-3″-hydroxyamentoflavone. Both CGY-1 and CGY-2 could significantly inhibit coughs induced by inhalation of citric acid. Further, they acted on the peripheral reflex pathway to inhibit cough after electrical stimulation of the superior laryngeal nerve in guinea pigs. CONCLUSIONS: These chemicals isolated from C. giganteum seeds showed good antitussive effects. The data provide scientific evidence to support the traditional use of C. giganteum seeds as an antitussive herbal medicine.

Contralateral R1 and R2 components of the laryngeal adductor reflex in humans under general anesthesia.

OBJECTIVES: To demonstrate that under total intravenous general anesthesia (TIVA), the contralateral R1 (cRI) and contralateral R2 (cR2) components of the laryngeal adductor reflex (LAR) can be reliably elicited; to determine effects of topical anesthesia and inhalational anesthesia on the LAR; and to discuss how this technique may be utilized to continuously monitor the vagus nerve reflex arc. STUDY DESIGN: Case series. METHODS: Vocal fold mucosa was electrically stimulated via endotracheal tube surface-based electrodes to elicit a LAR. Responses were recorded using the endotracheal tube electrode contralateral to the simulating electrode for each side. RESULTS: Twenty-one patients (31 nerves at risk), aged between 28 to 84 years, who underwent thyroid and cervical spine surgeries (4 males, 17 females) were included. cR1 responses were reliably elicited in all patients, and cR2 responses were obtained in 14 patients (66.6%). Mean cR1 latencies ± standard deviation were 22.5 ± 2.5 milliseconds (ms) (left) and 23.4 ± 3.3 ms (right). Mean cR1 amplitudes were 237.9 ± 153.9 microvolts (uV) (left) and 265.0 ± 226.5 uV (right). Mean R2 latencies were 59.8 ± 4.9 ms (left) and 61.8 ± 7.9 ms (right). Intraoperative reversible cR1 amplitude decreases correlated temporally with surgical maneuvers stretching or compressing the RLN or internal branch of the superior laryngeal nerve (iSLN). Inhalational anesthetic agents abolished cR2 and minimized cR1 at mean alveolar concentrations > 0.5. Topical lidocaine significantly reduced LAR amplitude. CONCLUSION: LAR cR1 and cR2 responses are present in humans under TIVA and may afford some airway protection against aspiration under anesthesia. They are inhibited by inhalational anesthetics and topical lidocaine. Continuous intraoperative iSLN and RLN monitoring are possible using surface-based endotracheal tube electrodes alone to stimulate and record cR1 responses. LEVEL OF EVIDENCE: 4. Laryngoscope, 127:E443-E448, 2017.

Central glucagon like peptide-1 inhibits reflex swallowing elicited by the superior laryngeal nerve via caudal brainstem in the rat.

The effects of glucagon like peptide-1 (GLP-1) on reflex swallowing were examined using anaesthetized rats. GLP-1 was injected into the dorsal vagal complex (DVC) using glass micropipettes. Swallowing was induced by repeated electrical stimulation of the central cut end of the superior laryngeal nerve (SLN) and was identified by the electromyogram lead penetrated in the mylohyoide muscle through bipolar electrodes. Microinjection of GLP-1 into the medial DVC (M-DVC) increased the frequency of swallowing during the electrical stimulation of the SLN and extended the latency of the first swallowing. Microinjection of GLP-1 into the lateral DVC (L-DVC) did not change the frequency of swallowing or the latency of the first swallowing. Neither the injection of vehicle into the M-DVC nor L-DVC affected swallowing frequency. Pre-injection of exendin (5-39), a GLP-1 receptor antagonist, attenuated the degree of suppression of swallowing frequency induced by the administration of GLP-1 in addition to shortening the latency of the first swallowing. To identify the effective site of GLP-1, lesion experiments were performed. Electrical lesion of the commissural part of the NTS (cNTS) and the vacuum removal of the area postrema (AP) did not affect the inhibition of reflex swallowing induced by the injection of GLP-1 into the M-DVC. Electrical lesion of the medial nucleus of the NTS (mNTS) and its vicinity abolished the inhibitory effects of swallowing induced by the injection of GLP-1. These results suggest that GLP-1 inhibits reflex swallowing via the mNTS in the dorsal medulla.

A novel methodology for assessing laryngeal and vagus nerve integrity in patients under general anesthesia.

OBJECTIVE: To describe a novel methodology for intraoperative neuro-monitoring of laryngeal and vagus nerves by utilizing the laryngeal adductor reflex (LAR). METHODS: Case series of 15 patients undergoing thyroid and cervical spine surgeries under total intravenous general anesthesia. Vocal fold mucosa was electrically stimulated to elicit a LAR using endotracheal tube based electrodes. Contralateral R1 (cR1) and R2 (cR2) responses were recorded using the endotracheal tube electrode contralateral to the simulating electrode. RESULTS: The LAR was reliably elicited in 100% of patients for the duration of each surgical procedure. Mean onset latency of cR1 response was 22.4±2.5ms (right) and 22.2±2.4ms (left). cR2 responses were noted in 10 patients (66.7%). No peri-operative complications or adverse outcomes were observed. CONCLUSIONS: The LAR is a novel neuro-monitoring technique for the vagus nerve. Advantages over current monitoring techniques including simplicity, ability to continuously monitor neural function without placement of additional neural probes and ability to assess integrity of both sensory and motor pathways. SIGNIFICANCE: The LAR represents a novel method for intraoperatively monitoring laryngeal and vagus nerves. The LAR monitors the entire vagus nerve reflex arc and is thus applicable to all surgeries where vagal nerve integrity may be compromised.

Recovery of laryngeal nerve function with sugammadex after rocuronium-induced profound neuromuscular block.

STUDY OBJECTIVE: The aim of this study was to evaluate the efficacy of sugammadex in reversing profound rocuronium-induced neuromuscular block at the laryngeal adductor muscles using motor-evoked potentials (mMEPs). DESIGN: A prospective observational study. SETTING: University surgical center. PATIENTS: Twenty patients with American Society of Anesthesiologists physical class I-II status who underwent propofol-remifentanil anesthesia for the surgery of the thyroid gland. INTERVENTIONS: Patients were enrolled for reversal of profound neuromuscular block (sugammadex 16 mg/kg, 3 minutes after rocuronium 1.2 mg/kg). To prevent laryngeal nerve injury during the surgical procedures, all patients underwent neurophysiologic monitoring using mMEPs from vocal muscles. At the same time, the registration of TOF-Watch acceleromyograph at the adductor pollicis muscle response to ulnar nerve stimulation was performed; recovery was defined as a train-of-four (TOF) ratio ≥0.9. MEASUREMENT AND MAIN RESULTS: After injection of 16 mg/kg of sugammadex, the mean time to recovery of the basal mMEPs response at the laryngeal adductor muscles was 70 ± 18.2 seconds. The mean time to recovery of the TOF ratio to 0.9 was 118 ± 80 seconds. In the postoperative period, 12 patients received follow-up evaluation of the vocal cords and no lesions caused by the surface laryngeal electrode during electrophysiological monitoring were noted. CONCLUSIONS: Recovery from profound rocuronium-induced block on the larynx is fast and complete with sugammadex. In urgent scenarios, "early" extubation can be performed, even with a TOF ratio ≤0.9. However, all procedures to prevent postoperative residual curarization should still be immediately undertaken.

The Food Contaminant Mycotoxin Deoxynivalenol Inhibits the Swallowing Reflex in Anaesthetized Rats.

Deoxynivalenol (DON), one of the most abundant mycotoxins found on cereals, is known to be implicated in acute and chronic illnesses in both humans and animals. Among the symptoms, anorexia, reduction of weight gain and decreased nutrition efficiency were described, but the mechanisms underlying these effects on feeding behavior are not yet totally understood. Swallowing is a major motor component of ingestive behavior which allows the propulsion of the alimentary bolus from the mouth to the esophagus. To better understand DON effects on ingestive behaviour, we have studied its effects on rhythmic swallowing in the rat, after intravenous and central administration. Repetitive electrical stimulation of the superior laryngeal nerve or of the tractus solitarius, induces rhythmic swallowing that can be recorded using electromyographic electrodes inserted in sublingual muscles. Here we provide the first demonstration that, after intravenous and central administration, DON strongly inhibits the swallowing reflex with a short latency and in a dose dependent manner. Moreover, using c-Fos staining, a strong neuronal activation was observed in the solitary tract nucleus which contains the central pattern generator of swallowing and in the area postrema after DON intravenous injection. Our data show that DON modifies swallowing and interferes with central neuronal networks dedicated to food intake regulation.

Dosage effect of rocuronium on intraoperative neuromonitoring in patients undergoing thyroid surgery.

The effect of different concentrations of rocuronium bromide used for anesthesia induction during thyroid surgery on the intraoperative recurrent laryngeal nerve monitoring was evaluated. One hundred patients undergoing thyroid operation were randomized into five groups (20 patients per group). Patients in group I were operated and monitored without the use of rocuronium bromide. Patients in groups II-V were respectively injected with 0.5x, 1x, 1.5x, and 2x ED95 rocuronium bromide intravenously. The time from injecting the rocuronium bromide to the beginning of tube insertion was recorded, the conditions of tracheal intubation were evaluated, and the changes in blood pressure and pulse during the intubation process were monitored. Vagus nerve/recurrent laryngeal nerve evoked muscle potential was monitored using the NIM-Response3.0 nerve electromyography monitor. The amplitude of electromyography signal was recorded every 5 min during 30 min after successful tracheal intubation. The tracheal intubation success rate was 100% in all groups. Compared with group I, intubating condition scores (Cooper scores) in the patients of groups II-V were higher (P < 0.05). The stability of intraoperative neuromonitoring signal amplitude in groups I-III met the monitoring standards. The findings suggest that the use of 0.5x or 1x ED95 rocuronium bromide during the anesthesia induction can improve the tracheal tube conditions without affecting the intraoperative recurrent laryngeal nerve monitoring. The use of 1x ED95 rocuronium bromide induction was associated with the best results.

Menthol suppresses laryngeal C-fiber hypersensitivity to cigarette smoke in a rat model of gastroesophageal reflux disease: the role of TRPM8.

Patients with gastroesophageal reflux disease (GERD) display enhanced laryngeal reflex reactivity to stimuli that may be due to sensitization of the laryngeal C-fibers by acid and pepsin. Menthol, a ligand of transient receptor potential melastatin-8 (TRPM8), relieves throat irritation. However, the possibility that GERD induces laryngeal C-fiber hypersensitivity to cigarette smoke (CS) and that menthol suppresses this event has not been investigated. We delivered CS into functionally isolated larynxes of 160 anesthetized rats. Laryngeal pH 5-pepsin treatment, but not pH 5-denatured pepsin, augmented the apneic response to CS, which was blocked by denervation or perineural capsaicin treatment (a procedure that blocks the conduction of C fibers) of the superior laryngeal nerves. This augmented apnea was partially attenuated by capsazepine [an transient receptor potential vanilloid 1 (TRPV1) antagonist], SB-366791 (a TRPV1 antagonist), and HC030031 [a transient receptor potential ankyrin 1 (TRPA1) antagonist] and was completely prevented by a combination of TRPV1 and TRPA1 antagonists. Local application of menthol significantly suppressed the augmented apnea and this effect was reversed by pretreatment with AMTB (a TRPM8 antagonist). Our electrophysiological studies consistently revealed that laryngeal pH 5-pepsin treatment increased the sensitivity of laryngeal C-fibers to CS. Likewise, menthol suppressed this laryngeal C-fiber hypersensitivity and its effect could be reversed by pretreatment with AMTB. Our results suggest that laryngeal pH 5-pepsin treatment increases sensitivity to CS of both TRPV1 and TRPA1, which are presumably located at the terminals of laryngeal C-fibers. This sensory sensitization leads to enhanced laryngeal reflex reactivity and augmentation of the laryngeal C-fiber responses to CS, which can be suppressed by menthol acting via TRPM8.

Central orexin inhibits reflex swallowing elicited by the superior laryngeal nerve via caudal brainstem in the rat.

We examined the effects of orexins on the reflex swallowing using anesthetized rats. Orexins were administered into the fourth ventricle. Swallowing was induced by repeated electrical stimulation of the central cut end of the superior laryngeal nerve (SLN) and was identified by the electromyogram lead penetrated the mylohyoid muscle through bipolar electrodes. The frequency of swallowing during the electrical stimulation of the SLN decreased after the administration of orexin-A in a dose-dependent manner. The latency of the first swallowing tended to be extended after the administration of orexin-A. The administration of orexin-B did not affect swallowing frequency. Pre-administration of SB334867, an orexin-1 receptor antagonist, attenuated the degree of inhibition of swallowing frequency induced by the administration of orexin-A. To identify the effective site of orexin-A, the effect of a microinjection of orexin-A into the dorsal vagal complex (DVC) was evaluated. Orexin-A was injected into one of the lateral DVC, the intermediate DVC, or the medial DVC. Microinjection of orexin-A into the medial DVC but not the other two sites decreased swallowing frequency. Pre-injection of SB334867 into the medial DVC disrupted the inhibitory response induced by fourth ventricular administration of orexin-A. The electrical lesion of the commissural part of the NTS, but not ablation of the AP, abolished the inhibition of reflex swallowing induced by fourth ventricular administration of orexin-A. These results suggest that orexin-A inhibits reflex swallowing via orexin-1 receptors situated in the commissural part of the NTS and/or its vicinity.

Laryngeal sensation and pharyngeal delay time after (chemo)radiotherapy.

The objective of the study was to evaluate the association between changes in laryngeal sensation and initiation of swallowing reflex or swallowing function before and after (chemo)radiotherapy. A prospective study was conducted in a tertiary referral university hospital. Thirteen patients who received (chemo)radiotherapy for treatment of laryngeal or hypopharyngeal cancer were included. Laryngeal sensation was evaluated at the tip of the epiglottis before and 1, 3 months, and 1 year after (chemo)radiotherapy. Videofluoroscopy was performed at the same time. Quantitative determinations included changes in laryngeal sensation, computed analysis of pharyngeal delay time, the distance and velocity of hyoid bone movement during the phase of hyoid excursion, and pharyngeal residue rate (the proportion of the bolus that was left as residue in the pharynx at the first swallow). Laryngeal sensation significantly deteriorated 1 month after (chemo)radiotherapy, but there was a tendency to return to pretreatment levels 1 year after treatment. Neither pharyngeal delay time nor displacement of the hyoid bone changed significantly before and after (chemo)radiotherapy. In addition, there was no significant difference in the mean velocity of hyoid bone movement and the amount of stasis in the pharynx at the first swallow before and after (chemo)radiotherapy. After (chemo)radiotherapy, laryngeal sensation deteriorated. But, in this study, videofluoroscopy showed that swallowing reflex and function were maintained.

Does topical anesthesia using aerosolized lidocaine inhibit the superior laryngeal nerve reflex?

OBJECTIVE: This study was designed to evaluate the effectiveness of topical lidocaine in attenuating the laryngeal reflex and blunting hemodynamic response by inhibition of the superior laryngeal nerve in laryngeal microsurgery, which would be helpful in preventing potential complications. STUDY DESIGN: A prospective, randomized, double-blind study. SETTING: Tertiary medical center. SUBJECTS AND METHODS: Fifty-four patients requiring glottic and supraglottic laryngeal microsurgery were randomly assigned to 1 of 2 groups, with equal numbers. Before surgery, 10% lidocaine was topically applied to the laryngeal surface of the epiglottis and vocal folds under direct vision in the study group and saline aerosol was applied in the control group. Heart rates, arterial blood pressure, and SPO2 were recorded at baseline, after induction, immediately before and after intubation, during the surgery, and upon extubation. Laryngospasm, agitation, and coughing were recorded during the recovery period. RESULTS: Heart rates, arterial pressure, and SPO2 did not differ significantly from baseline to postintubation period among the groups. SPO2 values measured similar in the remaining study. Heart rates and blood pressures were slightly decreased in the study group after lidocaine administration, but only blood pressure at pre- and post-extubation was significantly decreased in the study group (P < .05). Also laryngospasm and coughing were not statistically different between the 2 groups. There was an obvious gap between the 2 groups for agitation. Study group agitation was noted significantly lower (P < .05). CONCLUSION: These findings indicate that preoperative topical lidocaine application may be helpful in attenuating airway-circulatory reflexes in laryngeal microscopic surgery.

Laryngeal and tracheal afferent nerve stimulation evokes swallowing in anaesthetized guinea pigs.

We describe swallowing reflexes evoked by laryngeal and tracheal vagal afferent nerve stimulation in anaesthetized guinea pigs. The swallowing reflexes evoked by laryngeal citric acid challenges were abolished by recurrent laryngeal nerve (RLN) transection and mimicked by electrical stimulation of the central cut ends of an RLN. By contrast, the number of swallows evoked by upper airway/pharyngeal distensions was not significantly reduced by RLN transection but they were virtually abolished by superior laryngeal nerve transection. Laryngeal citric acid-evoked swallowing was mimicked by laryngeal capsaicin challenges, implicating transient receptor potential vanilloid 1 (TRPV1)-expressing laryngeal afferent nerves arising from the jugular ganglia. The swallowing evoked by citric acid and capsaicin and evoked by electrical stimulation of either the tracheal or the laryngeal mucosa occurred at stimulation intensities that were typically subthreshold for evoking cough in these animals. Swallowing evoked by airway afferent nerve stimulation also desensitized at a much slower rate than cough. We speculate that swallowing is an essential component of airway protection from aspiration associated with laryngeal and tracheal afferent nerve activation.

Desflurane but not sevoflurane augments laryngeal C-fiber inputs to nucleus tractus solitarii neurons by activating transient receptor potential-A1.

AIMS: Volatile anesthetics have distinct odors and some are irritating to the upper airway and may cause cough and laryngospasm, which may result, in part, from stimulation of C-fiber reflex. Local exposure of such anesthetics increases the sensitivity of capsaicin-sensitive laryngeal C-fiber endings compatible with airway irritability presumably by activation of transient receptor potential (TRP) ion channels, but the physiological relevance of this sensitization transmitted to the higher-order neurons in the central reflex pathway and output is unknown. MAIN METHODS: In anesthetized young guinea pigs, baseline and left atrial capsaicin evoked changes in the extracellular unit activity of laryngeal C-fiber-activated neurons in the nucleus tractus solitarii (NTS) and phrenic nerve activity were compared between irritant (desflurane) and non-irritant (sevoflurane) anesthetic gas exposure to the isolated larynx. KEY FINDINGS: Desflurane significantly augmented the peak and duration (p<0.01) of the NTS neuronal responses and the prolongation of expiratory time (p=0.017). The effect was enhanced by iontophoretic application of the TRPA1 agonist allyl-isothiocyanate (p<0.05), inhibited by TRPA1 antagonist HC-030031 (p<0.01), but not by TRPV1 antagonist BCTC. Sevoflurane did not affect the central pathway. SIGNIFICANCE: Thus, the sensitization of the laryngeal C-fiber endings by irritant volatile anesthetics is transmitted to the NTS via activation of the TRPA1 and is associated with a prolonged reflexively evoked expiratory apnea. The findings may help to explain local deleterious effects of irritant volatile general anesthetics on the airways during inhaled induction or bronchodilator therapy for status asthmatics.