Spontaneous breathing improves lung aeration in oleic acid-induced lung injury.
BACKGROUND
Experimental and clinical studies have shown reduction in intrapulmonary shunt with improved oxygenation by spontaneous breathing with airway pressure release ventilation (APRV) in acute lung injury. The mechanisms of these findings are not clear. The authors hypothesized that spontaneous breathing results in better aeration of lung tissue and that improvement in oxygenation can be explained by these changes. This hypothesis was studied in a porcine model of oleic acid-induced lung injury.


METHODS
Two hours after induction of lung injury, 24 pigs were randomly assigned to APRV with or without spontaneous breathing at a positive end-expiratory pressure of 5 cm H(2)O. Hemodynamics, spirometry, and end-expiratory lung volume by nitrogen washout were measured at baseline, after 2 h of lung injury, and after 2 and 4 h of mechanical ventilation in the specific mode. Finally, spiral computed tomography of the chest was performed at end-expiratory lung volume in 22 pigs.


RESULTS
Arterial carbon dioxide tension and mean and end-inspiratory airway pressures were comparable between settings. Four hours of APRV with spontaneous breathing resulted in improved oxygenation compared with APRV without spontaneous breathing (arterial oxygen tension, 144 +/- 65 vs. 91 +/- 50 mmHg, P < 0.01 for interaction time x mode), higher end-expiratory lung volume (786 +/- 320 vs. 384 +/- 148 ml, P < 0.001), and better aeration. End-expiratory lung volume and venous admixture were both correlated with the amount of lung reaeration (r(2) = 0.62 and r(2) = 0.61, respectively).


CONCLUSIONS
The results support the hypothesis that spontaneous breathing during APRV improves oxygenation mainly by recruitment of nonaerated lung and improved aeration of the lungs.
Wrigge
Hermann
H
Department of Anaesthesiology and Intensive Care Medicine, University of Bonn, Germany. hermann.wrigge@ukb.uni-bonn.de
Zinserling
Jörg
J
Neumann
Peter
P
Defosse
Jerome
J
Magnusson
Anders
A
Putensen
Christian
C
Hedenstierna
Göran
G
D000758:Anesthesia; D000818:Animals; D001784:Blood Gas Analysis; D003720:Densitometry; D006439:Hemodynamics / Q000502:physiology; D008171:Lung Diseases / Q000139:chemically induced* / Q000503:physiopathology*; D019301:Oleic Acid / Q000633:toxicity*; D010101:Oxygen Consumption / Q000502:physiology; D010366:Peak Expiratory Flow Rate; D012119:Respiration; D012121:Respiration, Artificial; D015656:Respiratory Mechanics / Q000502:physiology*; D013552:Swine; D014057:Tomography, X-Ray Computed
D019301:Oleic Acid