Effect of progressive mandibular advancement on pharyngeal airway size in anesthetized adults.

BACKGROUND General anesthesia in adult humans is associated with narrowing or complete closure of the pharyngeal airway. The purpose of this study was to determine the effect of progressive mandibular advancement on pharyngeal airway size in normal adults during intravenous infusion of propofol for anesthesia. METHODS Magnetic resonance imaging was performed in nine normal adults during wakefulness and during propofol anesthesia. A commercially available intraoral appliance was used to manually advance the mandible. Images were obtained during wakefulness without the appliance and during anesthesia with the participants wearing the appliance under three conditions: without mandibular advancement, advancement to 50% maximum voluntary advancement, and maximum advancement. Using computer software, airway area and maximum anteroposterior and lateral airway diameters were measured on the axial images at the level of the soft palate, uvula, tip of the epiglottis, and base of the epiglottis. RESULTS Airway area across all four airway levels decreased during anesthesia without mandibular advancement compared with airway area during wakefulness (P < 0.007). Across all levels, airway area at 50% advancement during anesthesia was less than that at centric occlusion during wakefulness (P = 0.06), but airway area with maximum advancement during anesthesia was similar to that during wakefulness (P = 0.64). In general, anteroposterior and lateral airway diameters during anesthesia without mandibular advancement were decreased compared with wakefulness and were restored to their wakefulness values with 50% and/or maximal advancement. CONCLUSIONS Maximum mandibular advancement during propofol anesthesia is required to restore the pharyngeal airway to its size during wakefulness in normal adults.