Effects of prone position and positive end-expiratory pressure on lung perfusion and ventilation

Crit Care Med. 2008 Aug;36(8):2373-80. doi: 10.1097/CCM.0b013e31818094a9.


Objectives: Prone positioning is frequently used during acute respiratory distress syndrome. However, mechanisms by which it improves oxygenation are poorly understood, as well as its interaction with positive end-expiratory pressure. This study was conducted to decipher the respective effects of positive end-expiratory pressure and posture during lung injury on regional lung ventilation, perfusion and recruitment assessed by positron emission tomography.

Design: Experimental study.

Setting: Research laboratory of a university hospital.

Subjects: Six female piglets.

Interventions: After oleic acid-induced lung injury, all animals were studied in supine and prone position at both positive end-expiratory pressure 0 and positive end-expiratory pressure 10 cm H2O.

Measurements and main results: In each experimental condition, regional lung perfusion and ventilation were assessed with positron emission tomograph using intravenous 15O-labeled water and inhaled nitrogen-13. Nonaerated lung weight was assessed with positron emission tomograph, and alveolar recruitment was defined as the difference of nonaerated lung weight between conditions. Positive end-expiratory pressure was associated with significant alveolar recruitment (130 +/- 85 and 65 +/- 29 g of lung in supine and prone position, respectively [p < 0.05 vs. 0]), whereas recruitment induced by posture was not statistically significant (77 +/- 97 g with positive end-expiratory pressure 0 and 13 +/- 19 g with positive end-expiratory pressure 10 [p > 0.05 vs. 0]). Regardless the posture, positive end-expiratory pressure redistributed both perfusion and ventilation toward dependent regions. Recruitment by positive end-expiratory pressure was restricted to dorsal regions in supine position, but extended diffusely along the ventral-to-dorsal dimension in prone position. Prone position was associated with recruitment in dorsal regions with concomitant derecruitment in ventral regions, magnitude of this being reduced by positive end-expiratory pressure. Prone position redistributed ventilation toward dorsal and ventral regions at positive end-expiratory pressure 0 and positive end-expiratory pressure, respectively. Finally, prone position redistributed perfusion toward ventral regions, to an extent amplified by positive end-expiratory pressure.

Conclusions: Positive end-expiratory pressure and posture act synergistically by redistributing lung regional perfusion toward ventral regions, but have antagonistic effects on regional ventilation.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Blood Gas Analysis
  • Disease Models, Animal*
  • Female
  • Hemodynamics*
  • Positive-Pressure Respiration*
  • Positron-Emission Tomography
  • Prone Position
  • Pulmonary Circulation
  • Respiration*
  • Respiratory Distress Syndrome / therapy*
  • Swine