Correlation Between Pulmonary Contusion Severity and Gas Exchange Parameters in a Rat Model of Blunt Thoracic Trauma

ABSTRACT Background: Pulmonary contusion is a common consequence of blunt chest trauma and a major contributor to respiratory dysfunction. This study aimed to evaluate the correlation between pulmonary contusion severity and key gas exchange indicators: alveolar-arterial oxygen gradient (AaDO2), partial pressure of oxygen (PaO₂), and PaO₂/FiO₂ (P/F) ratio in a controlled rat model. Methods: A post-treatment control group design was employed using 27 female Sprague-Dawley rats divided into three groups (n=9): (1) no-contusion control, (2) direct post-contusion, and (3) 48 hours post-contusion. Lung contusions were induced via blunt trauma by dropping a 200g weight from 1 meter onto the chest. Blood gas analysis and histopathological scoring were performed for edema, hemorrhage, and leukocyte infiltration. Results: Rats examined 48 hours post-contusion showed significantly elevated AaDO2 (mean 50,026.4) compared to the direct contusion group (33,393.4) and control (22,308.9). PaO₂ levels were lowest in the 48-hour post-contusion group (mean 70.61). The P/F ratio and PaO₂ were not significantly correlated with histopathological scores, while AaDO2 and AaDO2 augmentation showed strong positive correlations (r=0.687, p<0.001). Conclusion: Pulmonary contusion severity is significantly associated with increased AaDO2 and its augmentation, highlighting its potential as an early marker of impaired oxygenation. However, PaO₂ and P/F ratio showed limited correlation, indicating the complexity of gas exchange disruption in pulmonary injury. These findings support the utility of AaDO2 as a sensitive parameter for evaluating lung contusion severity in trauma settings. Keywords: Pulmonary contusion; AaDO2; PaO₂; P/F ratio; experimental trauma model; gas exchange