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To the Editor:—
The hiccup reflex is a series of brief, powerful, spasmodic inspiratory events accompanied by glottic closure. 1–2Two mechanisms that cause glottic closure during hiccups are possible. One is a passive process that results from suppression of laryngeal abductor muscles, such as posterior cricoarytenoid muscles. 2–5The other is an active process that results from activation of laryngeal adductor muscles, such as thyroarytenoid muscles. 4However, no data are available regarding the intralaryngeal muscle activities during human hiccups. The following report suggests that an active process is involved in glottic closure during hiccups in humans.
A 42-yr-old woman (height, 160 cm; weight, 58 kg) presented for laryngomicrosurgery. After anesthesia was induced rapidly using fentanyl (0.1 mg), thiopental (325 mg), and vecuronium (7 mg), the patient’s trachea was intubated with a 6.5-mm ID spiral tube, and anesthesia was maintained with nitrous oxide (66%), oxygen (33%), and isoflurane (0.5–1.5%). Approximately 30 min after induction, the patient abruptly experienced a series of spasmodic inspiratory efforts accompanied by glottic movements toward closure, which was observed through direct laryngoscopy. The glottic movements were recorded on a videotape recorder (video clip in Web Enhancement). To alleviate these spasmodic inspiratory events, we increased the inhalational isoflurane concentration from 0.7 to 2.0% and injected additional vecuronium (3 mg) intravenously. Approximately 1 min later, the inspiratory depth of these spasmodic inspiratory efforts gradually decreased, and they eventually stopped. Simultaneously, the glottic adduction gradually was attenuated and eventually stopped.
Most anesthesiologists conventionally use the term hiccups for this occurrence. Without a cuffed endotracheal tube, high-velocity airflow between the vocal cords could facilitate glottic closure during hiccups (Bernoulli effect). 2The presence of an endotracheal tube clearly ruled out the Bernoulli component. Moreover, the fact that neuromuscular blockade stopped glottic adduction indicates a possible contribution of laryngeal adductor muscles. The glottic adduction observed during this occurrence may involve an active process, possibly attributed to activation of laryngeal adductors. To our knowledge, this is the first report to indicate that there may be an active process in glottic closure during human hiccups. Further studies are needed to confirm this hypothetical contribution of laryngeal adductors.
The complication of hiccups that occur during laryngomicrosurgery during general anesthesia may provide a valuable opportunity for investigation of the mechanism that causes glottic closure during human hiccups.