Prone Position Improves Mechanics and Alveolar Ventilation in Acute Respiratory Distress Syndrome

Intensive Care Med. 2005 Feb;31(2):220-6. doi: 10.1007/s00134-004-2478-z. Epub 2004 Oct 13.


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.

Design: 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).

Conclusion: In severely hypoxemic patients, prone position was able to improve alveolar ventilation significantly by reducing the expiratory time constant.

MeSH terms

  • Analysis of Variance
  • Blood Gas Analysis
  • Female
  • Humans
  • Lung Compliance / physiology
  • Male
  • Middle Aged
  • Positive-Pressure Respiration
  • Prone Position / physiology*
  • Prospective Studies
  • Pulmonary Alveoli / physiopathology*
  • Respiration, Artificial*
  • Respiratory Distress Syndrome, Adult / physiopathology*
  • Respiratory Mechanics*
  • Statistics, Nonparametric