The diagnostic criteria for acute respiratory distress syndrome (ARDS) are the Berlin Criteria.

1. Timing – within 7 days of a known clinical insult or worsening respiratory symptoms
2. Imaging – Bilateral opacities not fully explained by effusions, atelectasis, or masses/nodules
3. Absence of cardiac failure or fluid overload
4. Hypoxemia – PaO2/FiO2 ≤ 300 mmHg with PEEP/CPAP ≥ 5 cmH2O

Reference

1. ARDS Definition Task Force.  Acute Respiratory Distress Syndrome – The Berlin Definition.  JAMA. 2012;307(23):2526-2533.
2. PulmCCM Blog.  Meet the New ARDS: Expert panel announces new definition, severity classes.
3. Life In The Fastlane Blog.  ARDS Definition.