Background: Mechanical ventilation is necessary during acute respiratory distress syndrome, but it promotes lung injury because of the excessive stretch applied to the aerated parenchyma. The authors' hypothesis was that after a regional lung injury, the noxious effect of mechanical ventilation on the remaining aerated parenchyma would be more pronounced.
Methods: Mice, instilled with hydrochloric acid (HCl) in the right lung, was assigned to one of the following groups: mechanical ventilation with tidal volumes (VT) 25 ml/kg (HCl-VILI25, n = 12), or VT 15 ml/kg (HCl-VILI15, n = 9), or spontaneous breathing (HCl-SB, n = 14). Healthy mice were ventilated with VT 25 ml/kg (VILI25, n = 11). Arterial oxygenation, lung compliance, bronchoalveolar lavage inflammatory cells, albumin, and cytokines concentration were measured.
Results: After 7 h, oxygenation and lung compliance resulted lower in HCl-VILI25 than in VILI25 (P < 0.05, 210 ± 54 vs. 479 ± 83 mmHg, and 32 ± 3.5 vs. 45 ± 4.1 µl/cm H2O, mean ± SD, respectively). After right lung injury, the left lung of HCl-VILI25 group received a greater fraction of the VT than the VILI25 group, despite an identical global VT. The number of total and polymorphonuclear cells in bronchoalveolar lavage resulted significantly higher in HCl-VILI25, compared with the other groups, in not only the right lung, but also in the left lung. The albumin content in the left lung resulted higher in HCl-VILI25 than in VILI25 (224 ± 85 vs. 33 ± 6 µg/ml; P < 0.05). Cytokines levels did not differ between groups.
Conclusion: Aggressive mechanical ventilation aggravates the preexisting lung injury, which is noxious for the contralateral, not previously injured lung, possibly because of a regional redistribution of VT.