Since the 1994 American-European Consensus Conference (AECC), the definition for acute respiratory distress syndrome (ARDS) has been widely used in both clinical practice and applied research. As all critical care practitioners are aware, however, the AECC definition has several problems.  For example, the term acute is ambiguous, the oxygenation criteria can be confounded by positive end-expiratory pressure (PEEP), and chest radiograph criteria are plagued by poor interobserver reliability. To address the problems with the AECC definition, a consensus process was initiated by an expert panel from the European Society of Intensive Care Medicine and endorsed by representatives from the American Thoracic Society and the Society of Critical Care Medicine.

After an expert panel was assembled and the background literature reviewed, the panel held in-person informal consensus discussions in September and October 2011, in Berlin, Germany, which led to a draft of the revised definition. The draft was empirically evaluated from October 2011 to January 2012, including an analysis of patient characteristics and distribution according to definition categories. In February 2012, follow-up consensus discussions and analysis, including evaluations of high-risk subsets and testing of predictive validity, were conducted. The finalized definition was published as a special communication in the June issue of The Journal of the American Medicine Association (JAMA).

Patient-level data from 4,188 patients from three single-center data sets were in the  evaluation of the Berlin Definition. Ancillary variables, such as respiratory system compliance, minute ventilation, radiographic severity, and PEEP, did not contribute to the predictive validity for severe ARDS and were removed from the definition. To compare the predictive validity of the AECC definition and the Berlin Definition, the area under the receiver operating curve (AUROC) was calculated. The final Berlin Definition had an AUROC of 0.58 (95% confidence interval [CI], 0.56-0.59) compared to the AECC definition (AUROC 0.54; 95% CI, 0.52-0.55; P<0.001) for predicting mortality. Stages of mild, moderate and severe ARDS, according to the Berlin Definition, were associated with increased mortality and increased median duration of mechanical ventilation in survivors. 

The Berlin Definition for ARDS addresses several of the limitations of the AECC definition. The final Berlin Definition consists of four components:

  1. Timing: within 1 week of a known clinical insult, or new or worsening respiratory symptoms
  2. Chest imaging: bilateral opacities—not fully explained by effusions, lobar/lung collapse or nodules
  3. Origin of edema: respiratory failure not fully explained by cardiac failure or fluid overload; if no risk factors present, echocardiography can be used to exclude hydrostatic edema (pulmonary artery catheter requirement is no longer necessary)
  4. Oxygenation: PaO2/FIO2 ratio: <200, 100-200, or <100 (with ≥5 cm H2O PEEP)

Although the Berlin Definition is still not perfect, it provides greater clarity and standardization for ARDS than the AECC definition. The process used to develop the Berlin Definition stands as a contemporaneous example of how consensus definition activities can be supported by empirical research to better define life-threatening conditions in both the clinical and research arenas. Readers also are encouraged to review Derek Angus’ excellent editorial on the Berlin Definition in the same issue of JAMA.

Concise Critical Appraisal is a regular feature authored by SCCM member Samuel M. Galvagno Jr., DO, PhD. Each installment highlights journal articles most relevant to the critical care practitioner.