title: Effects of prone position and positive end-expiratory pressure on lung perfusion and ventilation.
abstract: OBJECTIVE
  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.
  
  
  METHODS
  Experimental study.
  
  
  METHODS
  Research laboratory of a university hospital.
  
  
  METHODS
  Six female piglets.
  
  
  METHODS
  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.
  
  
  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.
authors.affiliation: Hospices civils de Lyon, Service de Réanimation Médicale et d'Assistance Respiratoire, Hôpital de la Croix Rousse, Lyon, France.
authors.forename: Jean-Christophe
authors.initials: JC
authors.lastname: Richard
authors.forename: Fabienne
authors.initials: F
authors.lastname: Bregeon
authors.forename: Nicolas
authors.initials: N
authors.lastname: Costes
authors.forename: Didier L E
authors.initials: DL
authors.lastname: Bars
authors.forename: Christian
authors.initials: C
authors.lastname: Tourvieille
authors.forename: Franck
authors.initials: F
authors.lastname: Lavenne
authors.forename: Marc
authors.initials: M
authors.lastname: Janier
authors.forename: Gaël
authors.initials: G
authors.lastname: Bourdin
authors.forename: Gérard
authors.initials: G
authors.lastname: Gimenez
authors.forename: Claude
authors.initials: C
authors.lastname: Guerin
mesh_terms: D000818:Animals; D001784:Blood Gas Analysis; D004195:Disease Models, Animal; D005260:Female; D006439:Hemodynamics; D011175:Positive-Pressure Respiration; D049268:Positron-Emission Tomography; D016684:Prone Position; D011652:Pulmonary Circulation; D012119:Respiration; D012128:Respiratory Distress Syndrome / Q000628:therapy*; D013552:Swine