Objective:To investigate the effect of early dexamethasone treatment on seawater immersion-induced acute lung injury after open chest trauma.Methods: Twenty-four animals were evenly randomized into three groups: control group (CG),seawater group(SG),and dexamethasone treatment group (DG).Animals in CG group only had open chest trauma,those in the SG group were exposed to seawater after open chest trauma,and those in the DG group were treated with dexamethasone (1 mg/kg) after exposed to seawater.The vital signs of animals,plasma osmotic pressure,lung permeability index (LPI),and peripheral white blood cell count were observed 0,2,4,6,and 8 h after trauma.The plasma samples and bronchoalveolar lavage fluid (BALF) were collected for testing the levels of cytokines (IL-1β,IL-8,and vWF,etc.) with ELISA kit.H-E staining was used to observe the pathological changes of the lung.Results: Compared with the SG group,the pathological changes were improved in the DG group; the plasma osmotic pressures were similar between the two groups; and the pulmonary permeability index was markedly decreased in the DG group (0.039±0.006 vs 0.055±0.002,P<0.05).Besides,the count of peripheral leukocyte(×109) and plasma IL-1β,IL-8,and vWF(pg/ml) were all markedly decreased in the DG group compared with the SG group(WBC: 21.52±3.21 vs 24.81±2.08； IL-1β：72.84±38.42 vs 131.90±35.39；IL-8：45.21±16.39 vs 88.26±6.66；vWF：0.47±0.08 vs 1.03±0.09,P<0.05).Conclusion: Early dexamethasone treatment can attenuate the inflammatory injury of the lung in dogs with open chest trauma after seawater immersion,providing more chance for further management.