Background: Factors that contribute to ventilator-induced barotrauma are not well defined. This study investigates the effects of posture on ventilator-induced barotrauma, as well as arterial oxygenation.
Methods: Twelve dogs with oleic acid lung injury, lying in the prone position (n = 6) and right lateral position (n = 6), were mechanically ventilated with continuous positive pressure ventilation for 24 hours. The incidence of pneumothorax and arterial oxygenation were investigated in each position.
Results: All animals lying in the lateral position developed pneumothorax in the nondependent thorax, while only one animal in the prone position developed pneumothorax in the left thorax (P < 0.05). Postmortem examination revealed that in the lateral group, the nondependent lung consisted of large areas of emphysematous regions and neutrophil infiltration regions, while the dependent lung was composed of extensive atelectasis and neutrophil infiltration. Lung ruptures occurred in the nondependent lung at the regions of either emphysematous change or severe neutrophil infiltration. In the prone group, in contrast, both lungs were inflated fairly homogeneously with only small areas of atelectatic and emphysematous changes. In the dog in whom pneumothorax developed, lung ruptures were limited to the regions of severe neutrophil infiltration in the left lung. No animal in either group had a peak airway pressure more than 20 cmH2O. The peak airway pressures were 17.5 +/- 1.3 cmH2O in the lateral group and 16.6 +/- 2.1 cmH2O in the prone group (P > 0.05). Tidal volume was comparable between the lateral group (13 +/- 2 ml/kg) and the prone group (12 +/- 1 ml/kg) before pneumothorax occurred (P > 0.05). Arterial oxygenation was much better in the prone group than in the lateral group during the experiment (P < 0.05).
Conclusion: It was concluded that in lung injury dogs, the prone position has beneficial effects on the incidence of ventilator-induced barotrauma and arterial oxygenation when compared with the lateral position. Ventilator-induced barotrauma may occur at lower airway pressure.