Sitting Posture Decreases Collapsibility of the Passive Pharynx in Anesthetized Paralyzed Patients with Obstructive Sleep Apnea

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Abstract
Background: Obstructive sleep apnea (OSA) is an independent risk factor for difficult and/or impossible mask ventilation during anesthesia induction. Postural change from supine to sitting improves nocturnal breathing in patients with OSA. The purpose of this study was to evaluate the effect of patient position on collapsibility of the pharyngeal airway in anesthetized and paralyzed patients with OSA. The authors tested the hypothesis that the passive pharynx is structurally less collapsible during sitting than during supine posture. Method: Total muscle paralysis was induced with general anesthesia in nine patients with OSA, eliminating neuromuscular factors contributing to pharyngeal patency. The cross-sectional area of the pharynx was measured endoscopically at different static airway pressures. Comparison of static pressure-area plots between the supine and sitting (62° head-up) allowed assessment of the postural differences of the mechanical properties of the pharynx. Results: : Maximum cross-sectional area was greater during sitting than during supine posture at both retropalatal (median (10th-90th percentile): 1.91 (1.52-3.40) versus 1.25 (0.65-1.97) cm) and retroglossal (2.42 (1.72-3.84) versus 1.75 (0.47-2.35) cm) airways. Closing pressure of the passive pharynx was significantly lower during sitting than supine posture. Differences of the closing pressures between the postures are 5.89 (3.73-11.6) and 6.74 (4.16-9.87) cm H2O, at retropalatal and retroglossal airways, respectively, and did not differ between the pharyngeal segments. Conclusions: Postural change from supine to sitting significantly improves collapsibility of pharyngeal airway in anesthetized and paralyzed patients with OSA.