Am J Respir Crit Care Med. 2013 Jan 24. [Epub ahead of print] PMID: 23348974

Rationale: Positive end-expiratory pressure (PEEP) and prone positioning may induce lung recruitment and affect alveolar dynamics in acute respiratory distress syndrome (ARDS). However, whether there is any interdependence between the effects of PEEP and prone positioning on these variables is unknown. Objectives: To determine the effects of high PEEP and prone positioning on lung recruitment, cyclic recruitment/derecruitment and tidal-hyperinflation, and how these effects are influenced by lung recruitability. Methods: Mechanically ventilated patients (VT 6 ml/kg IBW) underwent whole-lung computed tomography (CT) during breath-holding sessions at airway pressures of 5, 15, and 45-cmH2O, and Cine-CTs on a fixed thoracic transverse slice at PEEP 5 and 15-cmH2O. CT-images were repeated in supine and prone. A recruitment maneuver at 45- cmH2O was performed before each PEEP change. Lung recruitability was defined as the difference in percentage of non-aerated tissue between 5 and 45-cmH2O. Cyclic recruitment/derecruitment and tidal-hyperinflation were determined as tidal changes in percentage of non-aerated and hyperinflated tissue, respectively Main Results: 24 ARDS patients were included. Increasing PEEP from 5 to 15-cmH2O decreased non-aerated tissue (501±201 to 322±132grs, p<0.001) and increased tidal-hyperinflation (0.41±0.26 to 0.57±0.30%, p=0.004) in supine. Prone positioning further decreased non-aerated tissue (322±132 to 290±141grs, p=0.028), and reduced tidal-hyperinflation observed at PEEP 15 in supine (0.57±0.30 to 0.41±0.22%). Cyclic recruitment/derecruitment only decreased when high PEEP and prone were applied together (4.1±1.9 to 2.9±0.9%, p=0.003), particularly in patients with high lung recruitability. Conclusions: Prone positioning enhances lung recruitment and decreases alveolar instability and hyperinflation observed at high PEEP in ARDS patients.

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