The aim of this study was to determine a safe gastrointestinal contrast agent that could be used in various clinical situations where there is a risk of aspiration using a rabbit model.

30 healthy white rabbits were used. The rabbits were divided into 5 groups containing six animals each, one control group (anesthesia only) and 4 groups receiving various contrast agents [Solotop (Barium sulphate suspension), Gastrografin (Sodium and meglumine amidotrizoate), and Telebrix (Meglumine ioxitalamate), Visipaque (Iodixanol)]. The contrast agents were injected selectively into a main bronchus via a catheter inserted under fluoroscopy guidance. The rabbits were sacrificed either 1 day or 7 days after injecting the contrast agents, and the tissue reaction of the bronchi and lungs were examined both macro- and microscopically. The level of alveolar septal thickening, peribronchiolar lymphocytic infiltration, pulmonary congestion and edema, inflammatory exudate in the alveoli or bronchiolar lumina, microabscess formation, necrosis, pigmentation of materials injected, and fibropurulent pleurisy were evaluated and graded according to the severity as follows: no change, mild, moderate, marked in degree.

The common microscopic findings were alveolar septal thickening and peribronchiolar lymphocytic infiltration. Pulmonary congestion and edema, inflammatory exudate in the alveoli or bronchiolar lumina were observed in 21 out of 24 rabbits receiving the contrast agents. Pigmentation of the materials injected was observed only in the group receiving Solotop. An inflammatory exudate in the alveoli and bronchiolar/bronchial lumina, microabscess formation, and necrosis were noted in most groups, but was more frequent and severe in the group receiving Gastrografin.

The histopathological reactions of the rabbit lungs after the intrabronchial application of a contrast agent showed variable degrees of inflammatory reactions. Gastrografin produced most severe and extensive reaction, Solotop and Telebrix a moderate reaction, and Visipaque a minimal reaction. Therefore, a non-ionic dimeric contrast agent such as Visipaque may be the safest contrast agent in the lung when a GI tract examination is performed in clinical situations where there is a risk of aspiration.