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.