Objective: To explore the effect of lung strain on pulmonary edema in dogs with acute respiratory distress syndrome (ARDS) preliminarily.
Methods: Twenty dogs were recruited to induct ARDS models by venous injection of oleic acid and grouped into Group S1.0, S1.5, S2.0, S2.5 randomly, the lung strain was previously designated as 1.0, 1.5, 2.0 or 2.5 for each group. The ventilation was used to support the dogs for 24 hours with tidal volume calculated from lung strain, functional residual capacity and the volume recruitment by positive end expiratory pressure. Extra vascular lung water index (EVLWI) and pulmonary vascular permeability index (PVPI) were tested by thermodilution technique and wet to dry ratio of lung tissue was evaluated by weighing method.
Results: The tidal volume of Group S1.0, S1.5, S2.0, S2.5 was (7.5 ± 1.7), (13.9 ± 5.8), (17.9 ± 4.7) and (20.3 ± 7.9) ml/kg, respectively. After ventilation for 4 h, EVLWI in Group S2.0 and Group S2.5 were higher than them in Group S1.0 and Group S1.5 ((38.9 ± 6.5), (40.1 ± 7.7) vs (26.6 ± 5.2), (28.8 ± 5.4) ml/kg; F = 5.627, P = 0.009). At the end of study, PVPI of Group S2.5 increased significantly versus Group S1.0, S1.5 and S2.0 (16.7 ± 5.4 vs 7.0 ± 2.3, 9.2 ± 2.2, 11.5 ± 6.0; F = 4.329, P = 0.022). Wet to dry ratios of lung tissue in Group S2.0 and Group S2.5 were significantly higher than Group S1.0 and Group S1.5 (10.4 ± 1.2, 10.8 ± 1.5 vs 8.3 ± 1.2, 8.0 ± 2.2; F = 5.627, P = 0.009) after ventilation.
Conclusion: Lung strain above 2.0 aggravates pulmonary edema dramatically and the effect might be slight if lung strain was smaller than 1.5.