Etiologies, diagnostic work-up and outcomes of acute respiratory distress syndrome with no common risk factor: a prospective multicenter study

Background: Patients meeting the Berlin definition for the acute respiratory distress syndrome (ARDS) might lack exposure to one or more common risk factors and exhibit different clinical phenotype and outcomes. We aimed to compare the clinical presentation and outcome of ARDS patients with or without risk factors, the impact on hospital mortality, and to assess the diagnostic work-up performed. The current study is an ancillary analysis of an international, multicenter, prospective cohort study (the Large Observational Study to Understand the Global Impact of Severe Acute Respiratory Failure, LUNG SAFE). Patients meeting ARDS criteria within 2 days of acute hypoxemic respiratory failure onset were included in the study and categorized as having risk factors or not. Outcomes were compared using propensity score matching. Results: Among 2813 patients, 234 (8.3% [7.3-9.3]) had no ARDS risk factor identified. These were older, had more frequent chronic diseases and presented with less severe SOFA and non-pulmonary SOFA scores (p < 0.001). Compared to other ARDS, CT scan (32.1 vs 23.9%, p < 0.001) and open lung biopsy (2.6 vs 0.2%, p < 0.001) were slightly more frequent but left heart filling pressures assessment was not (69.4 vs 68.4%, p > 0.99). Among ARDS with no risk factor, 45 patients (19.2%) had a specific diagnosis made. As compared to others, patients having ARDS with no risk factor had a lower ICU but not hospital mortality (34.6 vs 40.0%; p = 0.12). A matched cohort analysis confirmed the lack of significant difference in mortality. Conclusion: Eight percent of ARDS patients have no identified risk factor, 80% of whom have no etiological diagnosis made. The outcome of ARDS with no risk factor was comparable to other ARDS but few had a comprehensive diagnostic work-up, potentially leading to missed curable diseases.