[Influence of combining positive end-expiratory pressure with prone position on acute respiratory distress syndrome in pig]

Abstract

Objective: To determine the effect of combining positive end-expiratory pressure (PEEP) with prone position during acute respiratory distress syndrome (ARDS) and its mechanism.

Methods: Twelve healthy pigs were randomly divided into two groups according to the body posture during mechanical ventilation after oleic acid-induced lung injury: supine position group and prone position group. Three different PEEP levels of 0 (ZEEP), 10 (PEEP10) and 20 cm H2O (PEEP20, 1 cm H2O=0.098 kPa) were applied to each group one after another. Hemodynamics, respiratory mechanics and gas exchange were measured 15 minutes after each PEEP level was applied, and lung specimens for pathological examination were harvested after sacrifice of the animals.

Results: Compared to supine position, prone position improved oxygenation index (PaO2/FiO2) at ZEEP and PEEP10 [ZEEP: (234.00+/-72.55) mm Hg vs. (106.58+/-34.93) mm Hg, PEEP10: (342.97+/-60.15) mm Hg vs. (246.80+/-83.69) mm Hg, 1 mm Hg=0.133 kPa, both P<0.05 ], but not at PEEP20. No significant difference in heart rate (HR), mean arterial pressure (MAP), cardiac index (CI), compliance of the respiratory system (Cst) and partial pressure of arterial carbon dioxide (PaCO2) were observed between groups at three PEEP levels. Compared with supine position, lung recruited volume (RV) was elevated in prone position at PEEP20 [(378.55+/-101.80) ml vs. (302.95+/-34.31) ml, P<0.05], but not at PEEP10. In supine group the dorsal regions of the lungs showed more severe injury than that in prone group (12.00+/-1.69 vs. 6.03+/-1.56, P<0.05).

Conclusion: In pigs with ARDS, prone position improves PaO2/FiO2 significantly without influence on respiratory mechanics and hemodynamics. Redistribution of lung injury may be one of the mechanisms of its beneficial effect.