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Purpose: Our objective was to revise the definition of acute respiratory distress syndrome (ARDS) using a conceptual model incorporating reliability and validity, and a novel iterative approach with formal evaluation of the definition. Methods: The European Society of Intensive Care Medicine identified three chairs with broad expertise in ARDS who selected the participants and created the agenda. After 2 days of consensus discussions a draft definition was developed, which then underwent empiric evaluation followed by consensus revision. Results: The Berlin Definition of ARDS maintains a link to prior definitions with diagnostic criteria of timing, chest imaging, origin of edema, and hypoxemia. Patients may have ARDS if the onset is within 1 week of a known clinical insult or new/worsening respiratory symptoms. For the bilateral opacities on chest radiograph criterion, a reference set of chest radiographs has been developed to enhance inter-observer reliability. The pulmonary artery wedge pressure criterion for hydrostatic edema was removed, and illustrative vignettes were created to guide judgments about the primary cause of respiratory failure. If no risk factor for ARDS is apparent, however, objective evaluation (e.g., echocardiography) is required to help rule out hydrostatic edema. A minimum level of positive end-expiratory pressure and mutually exclusive PaO/FiO thresholds were chosen for the different levels of ARDS severity (mild, moderate, severe) to better categorize patients with different outcomes and potential responses to therapy. Conclusions: This panel addressed some of the limitations of the prior ARDS definition by incorporating current data, physiologic concepts, and clinical trials results to develop the Berlin definition, which should facilitate case recognition and better match treatment options to severity in both research trials and clinical practice. [ABSTRACT FROM AUTHOR]