To study the correlation between the changes of the chest diffuse comet-tail sign and arterial oxygen partial pressure (PaO₂) in oleic acid-induced acute lung injury model.

Twenty-one Japanese big-eared white rabbits with normal lung ultrasound examination were selected. After anesthesia, the heart blood was collected and the arterial blood was detected. Then the pure oleic acid was injected according to 0.1 ml/kg dosage, which caused the chest diffuse comet-tail sign in rabbit lungs in 1 h. The PaO₂ values were measured by collecting blood from the heart at 1 h, 2 h, 3 h, 6 h, 9 h, 12 h, and 24 h after injection of oleic acid.

Blood sample was collected in 6 experimental rabbits at 1 h after injecting oleic acid. 4/6 experimental rabbits had higher PaO₂ than that before the injection. No significant changes were found in the other two experimental rabbits. The blood test showed that PaO₂ did not decrease at 2 h, 3 h, 6 h after injection of oleic acid, respectively. Two blood samples were collected at 9 hours after injection of oleic acid. PaO₂ increased in one case, and decreased in the other case. After 12 hours of molding, 5 blood samples were collected. PaO₂ increased in 2 cases, decreased in 2 cases, and failed in 1 case. After 24 hours of blood collection, 5 rats were found to have a significant decrease in PaO₂ compared with that before the model. On microscope, the pathologic findings were as followed: pulmonary edema, pulmonary congestion, and congestive bleeding occurred in the lungs of rabbits sacrificed from 1 to 24 h after oleic acid injection; Some experimental rabbits appeared alveolar collapse, pulmonary congestion necrosis, lung infarction, pulmonary fibrosis, etc; 12 experimental rabbits appeared pleural folds, of which 2 cases presented at 1 h (2/6), 5 cases presented at 24 h (4/5), and 6 cases presented at 2~12 h (6/9). The presence of pleural folds increased with the time after oleic acid injection.

The changes on ultrasonography in animal model of oleic acid-induced acute lung injury were present earlier than that of PaO. The individual differences in the experimental rabbits may lead the decrease of PaO₂ at different time points. PaO₂ decreased in all cases till 24 hours after the modeling. Pulmonary ultrasonography can be used for early imaging diagnosis of acute lung injury.