Effects of prone position and positive end-expiratory pressure on lung perfusion and ventilation.
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.
Richard
Jean-Christophe
JC
Hospices civils de Lyon, Service de Réanimation Médicale et d'Assistance Respiratoire, Hôpital de la Croix Rousse, Lyon, France.
Bregeon
Fabienne
F
Costes
Nicolas
N
Bars
Didier L E
DL
Tourvieille
Christian
C
Lavenne
Franck
F
Janier
Marc
M
Bourdin
Gaël
G
Gimenez
Gérard
G
Guerin
Claude
C
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