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

The Berlin Criteria for Acute Respiratory Distress Syndrome (ARDS)

The Berlin definition classifies ARDS into three severity categories based on the PaO₂/FiO₂ ratio: mild (201-300 mmHg), moderate (101-200 mmHg), and severe (≤100 mmHg), with each category associated with increasing mortality rates. 1, 2

Diagnostic Criteria for ARDS

The Berlin definition includes four key components:

1. Timing:

   • Onset within 1 week of a known clinical insult or new/worsening respiratory symptoms 3, 2

2. Chest Imaging:

   • Bilateral opacities on chest radiograph or CT scan
   • Not fully explained by effusions, lobar/lung collapse, or nodules 3, 2

3. Origin of Edema:

   • Respiratory failure not fully explained by cardiac failure or fluid overload
   • Objective assessment (e.g., echocardiography) needed to exclude hydrostatic edema if no risk factor is present 3, 2

4. Oxygenation:

   • Minimum PEEP requirement of ≥5 cmH₂O (or non-invasive CPAP)
   • Severity stratification based on PaO₂/FiO₂ ratio: 1, 2
     • Mild ARDS: 201-300 mmHg
     • Moderate ARDS: 101-200 mmHg
     • Severe ARDS: ≤100 mmHg

Clinical Implications of ARDS Severity

The severity categories correlate with important clinical outcomes:

• Mortality rates:

  • Mild: 27%
  • Moderate: 32%
  • Severe: 45-60% 1, 2

• Duration of mechanical ventilation (for survivors):

  • Mild: median 5 days
  • Moderate: median 7 days
  • Severe: median 9 days 2

Management Considerations Based on Severity

Management strategies should be tailored according to ARDS severity:

• Mild ARDS (PaO₂/FiO₂ 201-300 mmHg):

  • Low tidal volume ventilation (6 ml/kg PBW)
  • Lower PEEP (5-10 cmH₂O)
  • Target PaO₂ 70-90 mmHg 1

• Moderate ARDS (PaO₂/FiO₂ 101-200 mmHg):

  • Low tidal volume ventilation
  • Higher titrated PEEP
  • Target PaO₂ 70-90 mmHg 1

• Severe ARDS (PaO₂/FiO₂ ≤100 mmHg):

  • Low tidal volume ventilation
  • Higher titrated PEEP
  • Consider prone positioning (>12 hours/day)
  • Consider neuromuscular blockade (≤48 hours)
  • Consider ECMO in refractory cases 1

Important Clinical Considerations

• The Berlin definition removed the pulmonary artery wedge pressure criterion that was present in older definitions 3, 2
• Clinical judgment is sufficient to characterize hydrostatic edema unless no ARDS risk factor is apparent 3, 2
• The term "acute lung injury" was removed in the Berlin definition 4
• Plateau pressure should be maintained ≤30 cmH₂O and driving pressure <15 cmH₂O to minimize ventilator-induced lung injury 1

Recent Developments

A 2024 update to the Berlin definition (Global ARDS definition) proposes several modifications: 5

1. Including high-flow nasal oxygen with minimum flow rate ≥30 L/min
2. Using SpO₂/FiO₂ ≤315 (if SpO₂ ≤97%) as an alternative to PaO₂/FiO₂ for hypoxemia assessment
3. Adding ultrasound as an imaging modality, especially in resource-limited settings
4. Removing requirements for specific PEEP, oxygen flow rate, or respiratory support devices in resource-limited settings

These modifications aim to increase the applicability of the ARDS definition globally while maintaining its core conceptual framework.