Is it possible to predict which patients with mild pneumonias will develop hypoxemia?

Usually, mortality due to mild community-acquired pneumonias (CAP) (Pneumonia severity index (PSI) classes I-III) is low (<3%), but the appearance of hypoxemia significantly increases mortality. Our aim was to determine the clinical parameters associated with risk factors of developing hypoxemia in subjects with mild CAP (PSI I-III) and the clinical outcomes of the hypoxemic group. We analyzed clinical characteristics and the outcomes of patients with mild CAP and hypoxemia (PaO2/FiO2<300), in a prospective, multicenter cohort study of 1195 patients. Mild pneumonias (PSI I-III) were found in 645 cases (53.9%), of which 217 (33.6%) presented hypoxemia according to a PaO2/FiO2<300. Patients with PaO2/FiO2<300 required more ICU admissions, mechanical ventilation, and developed septic shock than other PSI I-III patients. The clinical parameters associated with hypoxemia were: COPD, bilateral chest X-ray involvement, and hypoalbuminemia. We conclude that patients with COPD, those with bilateral chest X-ray involvement, or hypoalbuminemia were significantly more likely to have hypoxemia in mild CAP. Hypoxemic patients with low-risk pneumonia have worse clinical outcomes, including more ICU admission, need for mechanical ventilation and presence of septic shock than non-hypoxemic low-risk patients.