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Table 1 The Berlin ARDS definition [1]

From: Comparison of the efficacy and safety of FP-1201-lyo (intravenously administered recombinant human interferon beta-1a) and placebo in the treatment of patients with moderate or severe acute respiratory distress syndrome: study protocol for a randomized controlled trial

Characteristic Mild ARDS Moderate ARDS Severe ARDS
Timing Acute onset within 1 week of a known clinical insult or new or worsening respiratory symptoms
Hypoxemia PaO2/FiO2
> 200– ≤ 300 mmHg
with PEEP or CPAP ≥ 5 cmH2O
PaO2/FiO2
> 100– ≤ 200 mmHg
with PEEP ≥ 5 cmH2O
PaO2/FiO2
≤ 100 mmHg
with PEEP ≥ 5 cmH2O
Origin of edema Respiratory failure associated with known ARDS risk factors and not fully explained by cardiac failure or fluid overload. An objective assessment of cardiac failure or fluid overload is needed if no ARDS risk factors are present
Radiological abnormalities (chest X-ray or CT scan) Bilateral opacities not fully explained by effusions, nodules, masses or lobar/lung collapse
  1. ARDS acute respiratory distress syndrome, CPAP continuous positive airway pressure, CT computed tomography, PaO 2 /FiO 2 partial pressure of oxygen/fraction of inspired oxygen, PEEP positive end-expiratory pressure