PRONE POSITIONING IMPROVES PULMONARY-FUNCTION IN OBESE PATIENTS DURING GENERAL-ANESTHESIA

We investigated the effects of prone position on functional residual c apacity (FRC), the mechanical properties (compliance and resistance) o f the total respiratory system, lung and chest wall, and the gas excha nge in 10 anesthetized and paralyzed obese (body mass index more than 30 kg/m(2)) patients, undergoing elective surgery. We used the esophag eal balloon technique together with rapid airway occlusions during con stant inspiratory flow to partition the mechanics of the respiratory s ystem into its pulmonary and chest wall components. FRC was measured b y the helium dilution technique. Measurements were taken in the supine position and after 15-30 min of prone position maintaining the same r espiratory pattern (tidal volume 12 mL/kg ideal body weight, respirato ry rate 14 breaths/min, fraction of inspired oxygen [FIO2] 0.4). We fo und that FRC and lung compliance significantly (P < 0.01) increased fr om the supine to prone position (0.894 +/- 0.327 L vs 1.980 +/- 0.856 L and 91.4 +/- 55.2 mL/cm H2O vs 109.6 +/- 52.4 mL/cm H2O, respectivel y). On the contrary, the prone position reduced chest wall compliance (199.5 +/- 58.7 mL/cmH(2)O vs 160.5 +/- 45.4 mL/cm H2O, P < 0.01), thu s total respiratory system compliance did not change. Resistance of th e total respiratory system, lung, and chest wall were not modified on turning the patients prone. The increase in FRC and lung compliance wa s paralleled by a significant (P < 0.01) improvement of PaO2 from supi ne 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 pul monary function, incre asing FRC, lung compliance, and oxygenation.