BENEFICIAL-EFFECTS OF THE PRONE POSITION ON THE INCIDENCE OF BAROTRAUMA IN OLEIC ACID-INDUCED LUNG INJURY UNDER CONTINUOUS POSITIVE PRESSURE VENTILATION

Background: Factors that contribute to ventilator-induced barotrauma a re not well defined. This study investigates the effects of posture on ventilator-induced barotrauma, as well as arterial oxygenation. Metho ds: Twelve dogs with oleic acid lung injury, lying in the prone positi on (n=6) and right lateral position (n=6), were mechanically ventilate d with continuous positive pressure ventilation for 24 hours. The inci dence of pneumothorax and arterial oxygenation were investigated in ea ch position. Results: All animals lying in the lateral position develo ped 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 nondep endent lung consisted of large areas of emphysematous regions and neut rophil infiltration regions, while the dependent lung was composed of extensive atelectasis and neutrophil infiltration. Lung ruptures occur red in the non-dependent lung at the regions of either emphysematous c hange or severe neutrophil infiltration. Ln the prone group, in contra st, both lungs were inflated fairly homogeneously with only small area s of atelectatic and emphysematous changes. Ln the dog in whom pneumot horax developed, lung ruptures were limited to the regions of severe n eutrophil infiltration in the left lung. No animal in either group had a peak airway pressure more than 20 cmH(2)O. The peak airway pressure s were 17.5+/-1.3 cmH(2)O in the lateral group and 16.6+/-2.1 cmH(2)O in the prone group (P>0.05). Tidal volume was comparable between the l ateral group (13+/-2 ml/kg) and the prone group (12+/-1 ml/kg) before pneumothorax occurred (P>0.05). Arterial oxygenation was much better i n 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-induce d barotrauma and arterial oxygenation when compared with the lateral p osition. Ventilator-induced barotrauma may occur at lower airway press ure.