title: Prone position improves mechanics and alveolar ventilation in acute respiratory distress syndrome.
abstract: OBJECTIVE
  We tested the hypothesis that ventilation in the prone position might improve homogenization of tidal ventilation by reducing time-constant inequalities, and thus improving alveolar ventilation. We have recently reported in ARDS patients that these inequalities are responsible for the presence of a "slow compartment," excluded from tidal ventilation at supportive respiratory rate.
  
  
  METHODS
  In 11 ARDS patients treated by ventilation in the prone position because of a major oxygenation impairment (PaO(2)/FIO(2)</=100 mm Hg) we studied mechanical and blood gas changes produced by a low PEEP (6+/-1 cm H(2)O), ventilation in the prone position, and the two combined.
  
  
  RESULTS
  Ventilation in the prone position significantly reduced the expiratory time constant from 1.98+/-0.53 s at baseline with ZEEP to 1.53+/-0.34 s, and significantly decreased PaCO(2) from 55+/-11 mm Hg at baseline with ZEEP to 50+/-7 mm Hg. This improvement in alveolar ventilation was accompanied by a significant improvement in respiratory system mechanics, and in arterial oxygenation, the latter being markedly increased by application of a low PEEP (PaO(2)/FIO(2) increasing from 64+/-19 mm Hg in supine position with ZEEP to 137+/-88 mm Hg in prone with a low PEEP).
  
  
  CONCLUSIONS
  In severely hypoxemic patients, prone position was able to improve alveolar ventilation significantly by reducing the expiratory time constant.
authors.affiliation: Medical Intensive Care Unit, University Hospital Ambroise Paré, Assistance Publique Hôpitaux de Paris, 9 avenue Charles de Gaulle, 92104, Boulogne Cedex, France.
authors.forename: Antoine
authors.initials: A
authors.lastname: Vieillard-Baron
authors.forename: Anne
authors.initials: A
authors.lastname: Rabiller
authors.forename: Karin
authors.initials: K
authors.lastname: Chergui
authors.forename: Olivier
authors.initials: O
authors.lastname: Peyrouset
authors.forename: Bernard
authors.initials: B
authors.lastname: Page
authors.forename: Alain
authors.initials: A
authors.lastname: Beauchet
authors.forename: François
authors.initials: F
authors.lastname: Jardin
mesh_terms: D000704:Analysis of Variance; D001784:Blood Gas Analysis; D005260:Female; D006801:Humans; D008170:Lung Compliance / Q000502:physiology; D008297:Male; D008875:Middle Aged; D011175:Positive-Pressure Respiration; D016684:Prone Position / Q000502:physiology*; D011446:Prospective Studies; D011650:Pulmonary Alveoli / Q000503:physiopathology*; D012121:Respiration, Artificial; D012128:Respiratory Distress Syndrome / Q000503:physiopathology*; D015656:Respiratory Mechanics; D018709:Statistics, Nonparametric