Unifying Concepts

Berlin Definition of the Acute Respiratory Distress Syndrome (ARDS)

The Berlin definition, proposed in 2012, breaks with tradition by establishing three risk strata that are based on the degree of hypoxemia as assessed at a minimum positive end-expiratory pressure (PEEP).

Berlin Definition of the Acute Respiratory Distress Syndrome (ARDS)



Onset within 7 days after a known clinical insult or new or worsening respiratory symptoms

Observational data suggest that ARDS will develop within 72 hr in the majority of patients at risk for the syndrome and within 1 wk in nearly all patients at risk

Bilateral opacities that are “consistent with pulmonary edema” on chest radiographs or chest CT

There is poor interobserver reliability in interpreting the chest radiograph for the presence of edema. To address this issue, the Berlin definition offers more explicit criteria (e.g., opacities should not be fully explained by effusions, lobar or lung atelectasis, or nodules or masses), with illustrative radiographs provided

Categorization of ARDS severity

A patient-level meta-analysis validated three thresholds for hypoxemia, all consisting of a Pao2:Fio2 ratio </=300 mm Hg


Pao2:Fio2, 201 to 300 mm Hg; mortality, 27% (95% CI, 24–30)


Pao2:Fio2, 101 to 200 mm Hg; mortality, 32% (95% CI, 29–34)


Pao2:Fio2, </=100 mm Hg; mortality, 45% (95% CI, 42–48)

Minimum PEEP setting or CPAP, 5 cm of water; Pao2:Fio2 assessed on invasive mechanical ventilation (CPAP criterion used for the diagnosis of mild ARDS)

Estimates of Fio2 are not accurate with oxygen-delivery systems other than invasive or noninvasive ventilation (with a tight-fitting mask), with the exception of nasal high-flow oxygen delivery systems (at flow rates >/=45 liters per minute); requiring higher PEEP settings does not increase predictive validity of the Berlin severity strata and adds complexity

CI denotes confidence interval, CPAP continuous positive airway pressure, Pao2:Fio2 ratio of the partial pressure of arterial oxygen to the fraction of inspired oxygen, and PEEP positive end-expiratory pressure.



  1. Thompson BT, Chambers RC, Liu KD. Acute Respiratory Distress Syndrome. N Engl J Med. 2017 Aug 10;377(6):562-572. [Medline]
  2. De Luis Cabezón N, Sánchez Castro I, Bengoetxea Uriarte UX, Rodrigo Casanova MP, García Peña JM, Aguilera Celorrio L. Acute respiratory distress syndrome: a review of the Berlin definition. Rev Esp Anestesiol Reanim. 2014 Jun-Jul;61(6):319-27. [Medline]
  3. Ferguson ND, Fan E, Camporota L, Antonelli M, Anzueto A, Beale R, Brochard L, Brower R, Esteban A, Gattinoni L, Rhodes A, Slutsky AS, Vincent JL, Rubenfeld GD, Thompson BT, Ranieri VM.The Berlin definition of ARDS: an expanded rationale, justification, and supplementary material. Intensive Care Med. 2012 Oct;38(10):1573-82. [Medline]


Created Oct 06, 2017.

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