The Prognostic Value of Alveolar-arterial Oxygen Gradient for Community-Acquired Pneumonia in the ED

ABSTRACT

PURPOSE: The purpose of this study was to investigate the value of the alveolar-arterial (A-a) oxygen gradient for patients with community-acquired pneumonia (CAP) in the emergency department (ED). METHODS: A prospective study of patients with CAP in the ED was performed. Patients with clinical and a radiographic diagnosis of CAP were enrolled. Inflammatory biomarkers, such as WBC (white blood cell) count, C-reactive protein (CRP), erythrocyte sedimentation rate (ESR), and A-a oxygen gradient were measured. The severity of CAP was assessed by three prediction rules The Pneumonia Severity Index (PSI), CURB65 (confusion, blood urea nitrogen, respiratory rate, blood pressure and age> or =65 yrs), and the Infectious Disease Society of America (IDSA) and American Thoracic Society (ATS) rules. The value of each biomarker (WBC, CRP, ESR) and A-a oxygen gradient for the prediction of mortality and CAP severity were assessed. RESULTS: A total of 126 patients with CAP were included. Sixteen patients, older and in the high-risk group, died within 30 days. Non-survivors had a significantly increased A-a oxygen gradient compared to survivors (91.20 vs. 46.71 mmHg, respectively; p<.01) and a high-sensitivity to C-reactive protein (158.57 vs. 91.28 mg/dL, respectively; p<.01). The median A-a oxygen gradient was significantly higher with severe disease based on the three prediction rules. In regression logistic analyses, the area under the receiver operating characteristic curve of the alveolar-arterial oxygen gradient was 0.807(95% confidence interval, 0.727-0.872). The addition of A-a oxygen gradient to the three prediction rules significantly increased the area under the receiver operating characteristic curve. CONCLUSION: These results suggest that A-a oxygen gradient is useful for the prediction of mortality and disease severity among CAP patients in the ED. The A-a oxygen gradient, as an adjunct to CAP prediction rules, may be worth while for the assessment of prognosis and severity.