Effect of High Dose Steroids on Oleic Acid-induced Lung Injury in Rabbits: CT Findings

ABSTRACT

PURPOSE: The purpose of this study is to evaluate the therapeutic efficacy, on the basis of CT findings, of high dose methyl prednisolone for treating acute lung injury that was induced by oleic acid injection. MATERIALS AND METHODS: A total of 30 healthy rabbits (1.8-2.2 kg) were included in this study. Group I included 10 rabbits in which 0.2 mL oleic acid was injected through their ear veins. Group IIa included 10 rabbits in which 30 mg/kg methyl prednisolone and 0.2 mL oleic acid were intravenously injected at the same time. Group IIb included 5 rabbits in which 30 mg/kg methyl prednisolone was injected 6 hours prior to the 0.2 mL oleic acid intravenous injection. The other 5 rabbits (Group III) were injected intravenously with 30 mg/kg methyl prednisolone without the oleic acid. After that, 30 mg/kg methyl prednisolone per every 12 hours was injected in the non-sacrificed rabbits of Group II and Group III. Nonenhanced Chest CT scans were performed prior to and 30 minutes, 4 hours, 24 hours, 48 hours, and 72 hours after the intravenous injection of oleic acid or methyl prednisolone. We randomly sacrificed one rabbit of groups I, II and III 30 minutes, 4 hours, 24 hours, 48 hours and 72 hours after CT scanning. The distribution, extent, and pattern of the lesions on the CT scan were analyzed. The analyzed pattern of the lesions was ground glass attenuation, consolidation and interstitial thickening. Pathologic correlation was then done. RESULTS: The main CT findings of Group I were peripheral, wedge shaped, ill-defined ground glass attenuations and/or consolidations. The pathologic findings of Group I were interstitial or intraalveolar edema, intraalveolar hemorrhage and coagulation necrosis. Diffuse ground glass opacities with interstitial thickening were noted in 20% (n=2/10) of Group I and in 60% (n=9/15) of Group II at the 30 minute CT; however, there was no statistical difference between the two groups (p=0.09). Consolidations with air bronchogram were noted in 22.2% (2/9) of Group I and in 38.5% (5/13) of Group II at the 4 hour CT. The main pathologic findings of consolidations were intraalveolar hemorrhage and coagulation necrosis. There was no statistical difference in the extent of the lesions between Group I and Group II (p=0.20, 0.14, 0.59 and 0.46 at 4, 24, 48 and 72 hours, respectively). The CT findings of Group IIa and Group IIb were not significantly difference. The CT findings of Group III were normal in all 5 rabbits. CONCLUSION: Because there was no significant difference for the extent of lung injury induced by oleic acid between the group treated with high dose methyl prednisolone and non-treated group on CT scans, high dose steroid therapy for acute respiratory distress syndrome and pulmonary fat embolism may not be effective in the acute stage.