A modified rat model of isolated bilateral pulmonary contusion.

The aim of the present study was to create a feasible specific rat model of isolated bilateral pulmonary contusion (PC) and to evaluate the relationship between severity of hypoxemia and quantity of contusion lesions. Anesthetized rats were placed in a prone position. Injury energy ranging from 2.1 to 3.0 J was produced by a falling weight passed through a specially designed arched shield to the bilateral chest wall of rats. After injury (4 h), the contusion volume was measured using computer-generated three-dimensional reconstruction from a chest computed tomographic scan and expressed as a percentage of total lung volume. Arterial partial pressure of oxygen (PaO(2)) in blood gas analysis and contusion volume percentage were used to assess the severity of contusion. Heart and lung biopsy was used to confirm the diagnosis and rule out the existence of myocardial contusion. There were 3 cases of death and 1 case of death in the 3.0 J and the 2.4 J group, respectively. PaO(2) in the 2.7 J group was significantly lower than that in the lower energy groups (P<0.001). The percentage of pulmonary contusion in the 2.7 J group was significantly higher compared to that of the lower energy groups (P<0.001). PaO(2) was negatively correlated with contusion percentage (R(2)=0.76). Hemorrhage, edema and neutrophil infiltration were determined by lung biopsy. No evidence of myocardial contusion was documented in multiple heart biopsies. The method illustrated in this research effectively duplicates isolated bilateral pulmonary contusion in rats, the severity of which is highly correlated with the contusion size. Thus, 2.7 J can be regarded as the maximal energy for sublethal injury.