Cardiorespiratory effects of spontaneous breathing in two different models of experimental lung injury: a randomized controlled trial.
BACKGROUND
Acute lung injury (ALI) can result from various insults to the pulmonary tissue. Experimental and clinical data suggest that spontaneous breathing (SB) during pressure-controlled ventilation (PCV) in ALI results in better lung aeration and improved oxygenation. Our objective was to evaluate whether the addition of SB has different effects in two different models of ALI.


METHODS
Forty-four pigs were randomly assigned to ALI resulting either from hydrochloric acid aspiration (HCl-ALI) or from increased intra-abdominal pressure plus intravenous oleic acid injections (OA-ALI) and were ventilated in PCV mode either with SB (PCV + SB) or without SB (PCV - SB). Cardiorespiratory variables were measured at baseline after induction of ALI and after 4 hours of treatment (PCV + SB or PCV - SB). Finally, density distributions and end-expiratory lung volume (EELV) were assessed by thoracic spiral computed tomography.


RESULTS
PCV + SB improved arterial partial pressure of oxygen/inspiratory fraction of oxygen (PaO2/FiO2) by a reduction in intrapulmonary shunt fraction in HCl-ALI from 27% +/- 6% to 23% +/- 13% and in OA-ALI from 33% +/- 19% to 26% +/- 18%, whereas during PCV - SB PaO2/FiO2 deteriorated and shunt fraction increased in the HCl group from 28% +/- 8% to 37% +/- 17% and in the OA group from 32% +/- 12% to 47% +/- 17% (P < 0.05 for interaction time and treatment, but not ALI type). PCV + SB also resulted in higher EELV (HCl-ALI: 606 +/- 171 mL, OA-ALI: 439 +/- 90 mL) as compared with PCV - SB (HCl-ALI: 372 +/- 130 mL, OA-ALI: 192 +/- 51 mL, with P < 0.05 for interaction of time, treatment, and ALI type).


CONCLUSIONS
SB improves oxygenation, reduces shunt fraction, and increases EELV in both models of ALI.
Varelmann
Dirk
D
Department of Anesthesiology and Intensive Care Medicine, University of Bonn, Sigmund-Freud-Strasse 25, D-53105 Bonn, Germany. dirk.varelmann@uni-bonn.de
Muders
Thomas
T
Zinserling
Jörg
J
Guenther
Ulf
U
Magnusson
Anders
A
Hedenstierna
Göran
G
Putensen
Christian
C
Wrigge
Hermann
H
D055371:Acute Lung Injury / Q000139:chemically induced*; D000818:Animals; D045422:Continuous Positive Airway Pressure / Q000379:methods; D023421:Models, Animal; D010101:Oxygen Consumption / Q000502:physiology; D011897:Random Allocation; D012119:Respiration; D015656:Respiratory Mechanics / Q000502:physiology*; D013548:Sweden; D013552:Swine