The reserch was based on describing oxygenation indices in relation to the compromise of lung parenchyma evaluated by diagnostic images of the thorax in patients with a diagnosis of lower respiratory tract infection. Retrospective cohort study in subjects who underwent oxygenation indices measurements and at least one chest CT scan with evidence of opacities, consolidation, pleural effusion, or no abnormal findings. A descriptive analysis was performed summarizing the qualitative variables in frequencies and percentages, and the quantitative variables in mean and standard deviation if their distribution was normal, median, and interquartile range if their distribution was not normal. A total of 3,150 patients were admitted to the final analysis, of whom 71.37% (2,248/3,150) had abnormal tomographic findings. The average age of the patients with opacity was 62.64 (SD: 18.15) compared to 60.69 (SD: 17.97) of the patients without opacity (p=0.014). SpO2/FiO2 was 8.72 average points lower (353.14 vs. 361.82; p=0.026) and PaO2/FiO2 was 12.61 average points lower (231.90 vs. 244.53; p=0.001) in patients with interstitial opacities versus patients without abnormal findings. SpO2/FiO2, SaO2, PaO2, and PaO2/FiO2 showed greater deterioration in patients with bilateral consolidation compared to patients without opacities (p<0.001, p<0.001, p<0.001, and p<0.001, respectively). Interstitial and/or alveolar opacities, consolidation, and pleural effusion present greater deterioration in oxygenation indices compared to patients without pulmonary involvement described in chest tomography.