Abstract
BackgroundThe open lung approach (OLA) reportedly has lung-protective effects against acute respiratory distress syndrome (ARDS). Recently, lowering of the driving pressure (ΔP), rather than improvement in lung aeration per se, has come to be considered as the primary lung-protective mechanism of OLA. However, the driving pressure-independent protective effects of OLA have never been evaluated in experimental studies. We here evaluated whether OLA shows protective effects against experimental ARDS even when the ΔP is not lowered.MethodsLipopolysaccharide was intratracheally administered to rats to establish experimental ARDS. After 24 h, rats were mechanically ventilated and randomly allocated to the OLA or control group. In the OLA group, 5 cmH2O positive end-expiratory pressure (PEEP) and recruitment maneuver (RM) were applied. Neither PEEP nor RM was applied to the rats in the control group. Dynamic ΔP was kept at 15 cmH2O in both groups. After 6 h of mechanical ventilation, rats in both groups received RM to inflate reversible atelectasis of the lungs. Arterial blood gas analysis, lung computed tomography, histological evaluation, and comprehensive biochemical analysis were performed.ResultsOLA significantly improved lung aeration, arterial oxygenation, and gas exchange. Even after RM in both groups, the differences in these parameters between the two groups persisted, indicating that the atelectasis-induced respiratory dysfunction observed in the control group is not an easily reversible functional problem. Lung histological damage was severe in the dorsal dependent area in both groups, but was attenuated by OLA. White blood cell counts, protein concentrations, and tissue injury markers in the broncho-alveolar lavage fluid (BALF) were higher in the control than in the OLA group. Furthermore, levels of CXCL-7, a platelet-derived chemokine, were higher in the BALF from the control group, indicating that OLA protects the lungs by suppressing platelet activation.ConclusionsOLA shows protective effects against experimental ARDS, even when the ΔP is not decreased. In addition to reducing ΔP, maintaining lung aeration seems to be important for lung protection in ARDS.
Highlights
The open lung approach (OLA) reportedly has lung-protective effects against acute respiratory distress syndrome (ARDS)
The dynamic ΔP (Fig. 2b) was maintained at 15 cmH2O throughout the experimental protocol until the final recruitment maneuver (RM). Both end-expiratory and end-inspiratory transpulmonary pressures were higher in the OLA group than in the control group, and transpulmonary driving pressures were kept at almost the same level between the two groups until the final RM (Additional file 1: Figure S1)
After the final RM, the tidal volume was set to the same value in both groups; dynamic ΔP was higher in the control group (20.9 ± 1.7 vs. 11.8 ± 1.1 cmH2O, p < 0.0001)
Summary
The open lung approach (OLA) reportedly has lung-protective effects against acute respiratory distress syndrome (ARDS). Lowering of the driving pressure (ΔP), rather than improvement in lung aeration per se, has come to be considered as the primary lung-protective mechanism of OLA. The driving pressure-independent protective effects of OLA have never been evaluated in experimental studies. We here evaluated whether OLA shows protective effects against experimental ARDS even when the ΔP is not lowered. Atelectasis in ARDS causes respiratory failure, and enhances lung injury through several mechanisms. Development of atelectasis during mechanical ventilation increases the relative tidal volume and the (driving pressure) [11, 12], which induces overdistension of aerated lung regions. Reducing atelectasis is an important aspect in the lungprotective management of ARDS
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