What are the latest Acute Respiratory Distress Syndrome (ARDS) criteria and treatment guidelines?

Latest ARDS Criteria and Management Guidelines

The latest ARDS criteria are defined by the 2024 Global Definition, which builds upon the Berlin Definition and includes patients on high-flow nasal oxygen, allows for SpO2:FiO2 measurements, and incorporates ultrasound as an imaging modality, particularly for resource-limited settings. 1

Current ARDS Diagnostic Criteria

Berlin Definition (2012) with 2024 Global Definition Updates

• Timing: Onset within 1 week of a known clinical insult or new/worsening respiratory symptoms 2
• Imaging: Bilateral opacities on chest radiography or CT scan not fully explained by effusions, collapse, or nodules
  • Update (2024): Ultrasound can now be used as an imaging modality, especially in resource-limited settings 1
• Origin of Edema: Respiratory failure not fully explained by cardiac failure or fluid overload
  • Clinical assessment is sufficient unless no risk factors are present, then objective evaluation is required 2
• Oxygenation: PaO₂/FiO₂ ratio ≤300 mmHg with PEEP or CPAP ≥5 cmH₂O
  • Update (2024): SpO₂/FiO₂ ≤315 (if SpO₂ ≤97%) can be used when arterial blood gases are unavailable 1
  • Update (2024): Includes patients on high-flow nasal oxygen with flow rates ≥30 L/min 1

Severity Classification

• Mild ARDS: 200 mmHg < PaO₂/FiO₂ ≤ 300 mmHg
• Moderate ARDS: 100 mmHg < PaO₂/FiO₂ ≤ 200 mmHg
• Severe ARDS: PaO₂/FiO₂ ≤ 100 mmHg 2

Important Clinical Consideration

• Reassess PaO₂/FiO₂ ratio at 24 hours after ARDS onset under standardized ventilator settings for more accurate assessment of lung injury severity 3, 4

Management Guidelines

Ventilation Strategy

• Initial Settings:

  • Volume-cycled ventilation with assist-control mode
  • Tidal volumes of 6 mL/kg predicted body weight
  • Plateau pressure <30 cmH₂O 3
  • Calculate ideal body weight:
    • Men: 50 + 2.3 (height in inches - 60)
    • Women: 45.5 + 2.3 (height in inches - 60) 3

• PEEP and Oxygenation:

  • Target arterial oxygen saturation ~90% (PaO₂ ~60-70 mmHg) 3
  • PEEP titration based on severity:
    • Mild ARDS: Lower PEEP (5-10 cmH₂O)
    • Moderate/Severe ARDS: Higher titrated PEEP 3

• Permissive Hypercapnia:

  • Accept elevated CO₂ levels while maintaining pH >7.20
  • Use caution in patients with increased intracranial pressure or significant cardiac dysfunction 3

Adjunctive Therapies

• Prone Positioning:

  • Recommended for severe ARDS (PaO₂/FiO₂ <100 mmHg)
  • Significantly reduces mortality 5, 3
  • Monitor for pressure injuries at facial pressure points 3

• Neuromuscular Blockade:

  • Consider short course (≤48 hours) for early severe ARDS with PaO₂/FiO₂ <150 mmHg
  • Helps prevent excessive transpulmonary pressure and manage ventilator dyssynchrony 3

• Corticosteroids:

  • Suggested for ARDS patients (conditional recommendation)
  • Benefits include reduced inflammatory response, decreased pulmonary edema
  • Should be initiated early (within 14 days of onset)
  • Monitor for adverse effects, particularly in immunocompromised patients 5, 3

• Venovenous ECMO (VV-ECMO):

  • Conditional recommendation for selected patients with severe ARDS
  • Consider when:
    • PaO₂/FiO₂ <80 mmHg or pH <7.25 with PaCO₂ >60 mmHg
    • Early ARDS (<7 days from onset)
    • Conventional therapies have failed
    • Reversible etiology present 5
  • Should be performed at high-volume, dedicated centers 5

Supportive Care

• Fluid Management:

  • Target neutral-to-negative fluid balance in established ARDS without evidence of tissue hypoperfusion 3

• Positioning:

  • Elevate head of bed 30-45 degrees to prevent ventilator-associated pneumonia 3

• Nutrition:

  • Provide enteral nutrition when appropriate 3

• Prophylaxis:

  • Implement stress ulcer and venous thromboembolism prophylaxis 6

Diagnostic Workup

• Identify Underlying Cause:
  • Most cases associated with pneumonia or sepsis 6
  • If no obvious cause, consider bronchoalveolar lavage to identify microorganisms 7
  • Blood samples for microorganisms and biomarkers of infection 7
  • Consider CT scan for suspected intra-abdominal sepsis or certain pneumonias 7
  • Ultrasonography to evaluate cardiac function, pleural effusions, and pneumothorax 7
  • In selected cases with inconclusive workup, consider open lung biopsy 7

Emerging Concepts

• Heterogeneity in ARDS:

  • Variation in presentation on aetiological, physiological, and biological levels 5
  • Deeper phenotyping may identify specific treatable traits and endotypes 5
  • Precision medicine approach may improve future therapeutic trials 5

• Weaning from Mechanical Ventilation:

  • Initiate weaning as soon as possible with daily spontaneous breathing trials 3
  • Monitor for readiness to wean based on improvement in underlying condition and respiratory parameters

• Post-ARDS Care:

  • Survivors at risk for diminished functional capacity, mental illness, and decreased quality of life 6
  • Ongoing care by primary care physician beneficial for these patients 6