Oxygen Saturations Less than 92% Are Associated with Major Adverse Events in Outpatients with Pneumonia: A Population-Based Cohort Study

Background. Patients with hypoxemia (blood oxygen saturation <90%) are usually hospitalized, although validated criteria (eg, the Pneumonia Severity Index [PSI]) suggest outpatient treatment is safe. We sought evidence to support or refute the practice. Methods. All patients in Edmonton, Alberta, Canada with pneumonia assessed at any of 7 emergency departments (EDs) and then discharged were enrolled in a population-based cohort study. The independent variable of interest was oxygen saturation; the outcome was the composite endpoint of 30-day mortality or hospitalization. Results. The study evaluated 2923 individuals with pneumonia who were treated as outpatients at any of 7 EDs. The patients' mean age (standard deviation [SD]) was 52 (20) years; 47% were women; 74% were low risk (PSI Class I-II). The mean blood oxygen saturation (SD) was 95% (3%); 126 patients (4%) had blood oxygen saturations <90%, and 201 patients (7%) had blood oxygen saturations of 90%-92%. Over 30 days, 39 patients (1%) died and 252 (9%) reached the composite endpoint. Compared with patients with higher blood oxygen saturations, those discharged with saturations <90% had significantly (P < .001) higher rates of 30-day mortality (7 [6%] vs 32 [1%]), hospitalization (23 [18%] vs 201 [7%]), and composite endpoints (27 [21%] vs 225 [8%]). Blood oxygen saturation <90% was independently associated with 30-day mortality or hospitalization (adjusted odds ratio (OR), 1.7; 95% confidence interval (CI) 1.1-2.8; P = .032). If the saturation threshold for hospitalization was 92%, then there was no association with adverse events (adjusted OR 1.1, 95% CI 0.8-1.7, P = .48). Raising the admission threshold to 92% entails 1 additional hospitalization for every 14 patients discharged. Conclusions. Among outpatients with pneumonia, oxygen saturations <90% were associated with increased morbidity and mortality. Our results indicate a hospital admission threshold of <92% would be safer and clinically better justified.