Acute respiratory distress syndrome — definition and severity by PaO₂/FiO₂
Onset within 1 week of a known insult or new/worsening respiratory symptoms
Bilateral opacities on chest imaging, not fully explained by effusion, collapse or nodules
Respiratory failure not fully explained by cardiac failure or fluid overload
On PEEP or CPAP ≥ 5 cmH₂O
PaO₂
FiO₂ (fraction, e.g. 0.6)
Enter PaO₂ and FiO₂
Evidence
Original publication
ARDS Definition Task Force; Ranieri VM, Rubenfeld GD, Thompson BT, et al. Acute respiratory distress syndrome: the Berlin Definition. Replaced the 1994 AECC definition: fixed timing (≤ 1 week), removed the term "acute lung injury", required PEEP/CPAP ≥ 5 cmH2O, and graded severity by PaO2/FiO2 (mild/moderate/severe), which stratified mortality (27%, 32%, 45%).
JAMA, 2012
Open source
Guideline
If no ARDS risk factor is present, hydrostatic (cardiogenic) oedema must be objectively excluded (e.g. echocardiography). Severity should be assessed on standardised ventilator settings; the ratio can be affected by PEEP and FiO2. A 2023 global definition additionally recognises ARDS on high-flow nasal oxygen ≥ 30 L/min and by SpO2/FiO2 — check which definition your unit uses.
Last reviewed: 2026-09
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