Objective: To evaluate the effects of positive end-expiratory pressure (PEEP) targeting optimal oxygenation on local gas distribution and inflammation in dogs with acute respiratory distress syndrome (ARDS).
Methods: ARDS was induced by saline alveoli-lavage and oleic acid intravenous. The animals were mechanical ventilated 4 h at optimal PEEP titrated by oxygenation. Computed tomography (CT) scans were performed before and after induction of ARDS and at the end the study. NF-κB was measured by electrophoretic mobility shift assay (EMSA), IL-6 and IL-10 were assessed by ELISA. Myeloperoxidase (MPO) and malondialdehyde (MDA) were measured. Pathological changes were examined under optical microscope.
Results: (1) Compared to baseline, total lung volumes decreased and nonaerated areas increased significantly after the induction of ARDS in both groups (P < 0.05). Compared with ARDS models, PEEP titrated to achieve optimal oxygenation resulted in greater lung recruitment but was accompanied with hyperinflation, hyperinflation occurred in non-dependent lung. Compared with oleic acid-injured ARDS, the changing of hyperinflated lung areas was increased markedly in saline lavage-injured ARDS (P < 0.05). (2) Compared with right lung ventral lower lobe, lung injury score was lower in right lung upper lobe. Histological injury in right lung dorsal lower lobe was severer than that in right lung upper lobe and right lung ventral lower lobe. NF-κB activation of right lung dorsal lower lobe was markedly higher than right lung upper lobe (P < 0.05). MPO and MDA were much higher with right lung dorsal lower lobe than right lung upper lobe and right lung ventral lower lobe (P < 0.05). Compared with right lung upper lobe and right lung ventral lower lobe, IL-6 and IL-10 increased markedly in right lung dorsal lower lobe (P < 0.05).
Conclusions: Alveolar hyperinflation and aggravated lung injury in non-dependent region were occurred at PEEP targeting optimal oxygenation. Hyperinflation was more common in saline lavage-injured ARDS.