What are the Berlin criteria for defining Acute Respiratory Distress Syndrome (ARDS)?

Berlin Criteria for ARDS Definition

The Berlin Definition requires four essential components: acute onset within 1 week of a known clinical insult or new/worsening respiratory symptoms, bilateral opacities on chest imaging not fully explained by effusions/atelectasis/nodules, respiratory failure not fully explained by cardiac failure or fluid overload, and impaired oxygenation classified by PaO₂/FiO₂ ratio with minimum PEEP of 5 cmH₂O. 1, 2, 3

Timing Criterion

• Onset must occur within 1 week of a known clinical insult or development of new or worsening respiratory symptoms 1, 2, 3
• This temporal requirement distinguishes ARDS from chronic or subacute lung processes 3

Imaging Criterion

• Bilateral opacities must be present on chest radiograph or CT scan 1, 2
• These opacities cannot be fully explained by pleural effusions, lobar/lung collapse, or nodules 1, 4
• A reference set of chest radiographs has been developed to enhance inter-observer reliability and standardize interpretation 3

Origin of Edema Criterion

• Respiratory failure cannot be fully explained by cardiac failure or fluid overload 1, 2
• The pulmonary artery wedge pressure criterion from prior definitions was removed 3
• If no clear ARDS risk factor is apparent, objective assessment (such as echocardiography) is required to exclude hydrostatic pulmonary edema 1, 4

Oxygenation Criterion and Severity Classification

All severity categories require measurement with minimum PEEP of 5 cmH₂O: 1, 5, 2

• Mild ARDS: 200 mmHg < PaO₂/FiO₂ ≤ 300 mmHg with PEEP or CPAP ≥5 cmH₂O 1, 5, 2

  • Associated with 27% mortality (95% CI, 24%-30%) 2
  • Median mechanical ventilation duration of 5 days (IQR, 2-11) in survivors 2

• Moderate ARDS: 100 mmHg < PaO₂/FiO₂ ≤ 200 mmHg with PEEP ≥5 cmH₂O 1, 5, 2

  • Associated with 32% mortality (95% CI, 29%-34%) 2
  • Median mechanical ventilation duration of 7 days (IQR, 4-14) in survivors 2

• Severe ARDS: PaO₂/FiO₂ ≤ 100 mmHg with PEEP ≥10 cmH₂O 1, 5, 2

  • Associated with 45% mortality (95% CI, 42%-48%) 2
  • Median mechanical ventilation duration of 9 days (IQR, 5-17) in survivors 2
  • Prone positioning is specifically recommended for this severity category 5

Critical Pitfalls to Avoid

• Always calculate PaO₂/FiO₂ ratio with patients on at least 5 cmH₂O of PEEP to avoid misclassification of severity 5, 4
• Misattribution of pulmonary edema to non-cardiogenic causes when cardiac failure is actually present leads to incorrect diagnosis 5, 4
• The Berlin Definition has better predictive validity for mortality compared to the prior American-European Consensus Conference definition (area under ROC 0.577 vs 0.536, P < .001) 2
• The definition inherently creates heterogeneity by not requiring specific etiological, physiological, or biological criteria, which may explain why many targeted therapies have failed in clinical trials 1