Prone Positioning Improves Pulmonary Function in Obese Patients During General Anesthesia

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Abstract
S, undergoing elective surgery.We used the esophageal balloon technique together with rapid airway occlusions during constant inspiratory flow to partition the mechanics of the respiratory system into its pulmonary and chest wall components. FRC was measured by the helium dilution technique. Measurements were taken in the supine position and after 15-30 min of prone position maintaining the same respiratory pattern (tidal volume 12 mL/kg ideal body weight, respiratory rate 14 breaths/min, fraction of inspired oxygen [FIO2] 0.4). We found that FRC and lung compliance significantly (P < 0.01) increased from the supine to prone position (0.894 +/- 0.327 L vs 1.980 +/- 0.856 L and 91.4 +/- 55.2 mL/cm H2 O vs 109.6 +/- 52.4 mL/cm H2 O, respectively). On the contrary, the prone position reduced chest wall compliance (199.5 +/- 58.7 mL/cm H2 O vs 160.5 +/- 45.4 mL/cm H2 O, P < 0.01), thus total respiratory system compliance did not change. Resistance of the total respiratory system, lung, and chest wall were not modified on turning the patients prone. The increase in FRC and lung compliance was paralleled by a significant (P < 0.01) improvement of PaO2 from supine to prone position (130 +/- 31 vs 181 +/- 28 mm Hg, P < 0.01), while PaCO2 was unchanged. We conclude that, in anesthetized and paralyzed obese subjects, the prone position improves pulmonary function, increasing FRC, lung compliance, and oxygenation. (Anesth Analg 1996;83:578-83)...