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

Berlin Criteria for ARDS

The Berlin Definition requires four components to be present simultaneously: 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/nodules/collapse, respiratory failure not fully explained by cardiac failure or fluid overload, and hypoxemia with PaO₂/FiO₂ ≤300 mmHg measured with minimum PEEP of 5 cmH₂O. 1, 2

Timing Criterion

• Onset must occur within 1 week of a known clinical insult or new/worsening respiratory symptoms 1, 3
• This 7-day window replaced the vague "acute" terminology from prior definitions 2

Imaging Criterion

• Bilateral opacities must be present on chest radiograph or CT scan 1, 3
• These opacities cannot be fully explained by effusions, lobar/lung collapse, or nodules 1
• A reference set of chest radiographs was developed to enhance inter-observer reliability and reduce diagnostic variability 3

Origin of Edema Criterion

• Respiratory failure must not be fully explained by cardiac failure or fluid overload 1, 2
• The pulmonary artery wedge pressure requirement was removed from the Berlin Definition 3, 2
• If no clear ARDS risk factor exists, objective evaluation (echocardiography) is required to exclude cardiogenic pulmonary edema 1, 3
• Clinical judgment suffices when an obvious ARDS risk factor is present 3

Hypoxemia Criterion

• PaO₂/FiO₂ ratio must be ≤300 mmHg 1, 2
• Measurement requires minimum PEEP of 5 cmH₂O - this is mandatory and non-negotiable 1, 3, 2
• Arterial blood gas is required to determine the PaO₂/FiO₂ ratio 1

Severity Classification

The Berlin Definition stratifies ARDS into three mutually exclusive severity categories based on degree of hypoxemia (all measured with minimum PEEP 5 cmH₂O): 1, 2

• Mild ARDS: 200 mmHg < PaO₂/FiO₂ ≤ 300 mmHg
• Moderate ARDS: 100 mmHg < PaO₂/FiO₂ ≤ 200 mmHg
• Severe ARDS: PaO₂/FiO₂ ≤ 100 mmHg

These severity categories correlate with mortality: mild ARDS has 27% mortality, moderate ARDS has 32% mortality, and severe ARDS has 45% mortality 2. Duration of mechanical ventilation in survivors also increases with severity (median 5,7, and 9 days respectively) 2.

Critical Pitfalls to Avoid

• Never calculate PaO₂/FiO₂ ratio without at least 5 cmH₂O PEEP - this will lead to misclassification of severity 1
• Standard chest radiographs are poor predictors of oxygenation severity or clinical outcome, but remain necessary for diagnosis 1
• Conditions like diffuse interstitial lung diseases, diffuse pulmonary infections, and drug-induced lung injury can present identically to ARDS and fall within the syndrome definition, but may require specific treatments rather than standard ARDS management 1
• Only a minority of patients meeting Berlin criteria actually have diffuse alveolar damage on autopsy, highlighting the heterogeneity captured by clinical diagnostic criteria 1
• The Berlin Definition does not account for patients on high-flow nasal oxygen, who may meet all other criteria but lack the minimum PEEP requirement 4