Background  Acute lung injury (ALI), characterized by the destruction of the blood–air barrier, is a common clinical emergency. However, in vivo evaluations of the structural and functional changes to the barrier caused by ALI are limited.

Objective To explore a real-time visualization method based on confocal laser endomicroscopy (CLE) to examine the permeability of the blood–air barrier in living rats with seawater drowning ALI.

Methods Ten SD rats were randomly divided into control group and seawater drowning group (SW group), with 5 rats in each group. The model of seawater drowning ALI was established using the intratracheal instillation of artificial seawater in the SW group. Three hours after modeling, the window-opening surgery was performed; four hours after modeling, FITC-Dextran was injected through a femoral vein catheter. The control group did not carry out seawater instillation, while the rest of the procedure was identical to that of the SW group. The lung’s right inferior lobe was then observed in vivo for 30 minutes using CLE. The leakage index of FITC-Dextran and the uniformity of the fluorescence distribution of the confocal images were then analyzed. Lung tissue, peripheral blood, and bronchoalveolar lavage fluid (BALF) were collected for the histopathological examination and determination of the FITC-Dextran leakage volume, the protein content of BALF, and the wet-to-dry (W/D) weight ratio of the lung tissue, respectively.

Results Following the intravenous administration of FITC-Dextran, the real-time images of pulmonary microcirculation and alveolar structure were observed using CLE. In the SW group, the vascular structures grew blurred over time, and there was a significantly higher leakage index than the control group at all time points (P<0.05). Additionally, the variation coefficients of the fluorescence distribution at different time points were lower in the SW group (P<0.05). The leakage volume of FITC-Dextran, the protein content of BALF, and the wet-to-dry weight ratio of the lung tissue were all higher in the SW group as well (P<0.05). Moreover, the results of the in vivo imaging were found to be consistent with that of the in vitro methods.

Conclusion Seawater drowning causes disruption of the lung tissue structure and increases pulmonary permeability in rats. Confocal laser endomicroscopy can be used to observe the lung tissue structure in living rats in vivo and investigate the pulmonary permeability of rats with seawater drowning ALI through quantitative analysis of confocal images.