ARDS Diagnosis and Management
Diagnostic Criteria
Diagnose ARDS using the Berlin Definition criteria: acute onset (within one week of known insult), bilateral pulmonary opacities on chest imaging not fully explained by effusions/atelectasis/nodules, PaO₂/FiO₂ ratio ≤300 mmHg with minimum PEEP of 5 cmH₂O, and respiratory failure not fully explained by cardiac failure or fluid overload. 1, 2
Severity Classification by PaO₂/FiO₂ Ratio:
Key Diagnostic Pitfalls:
- Differentiate from cardiogenic pulmonary edema by assessing for signs of fluid overload and cardiac dysfunction 2
- Ensure bilateral opacities cannot be explained by pleural effusion, atelectasis, or nodules alone 4
Initial Respiratory Support Strategy
For mild ARDS, consider high-flow nasal cannula (HFNC) starting at 30-40 L/min with FiO₂ 50-60%, but proceed to early intubation in a controlled setting if deterioration occurs within 1 hour rather than waiting for emergent intubation. 4, 1
HFNC Guidelines:
- Delivers up to 60 L/min gas flow with FiO₂ up to 1.0 4
- If requiring FiO₂ >70% and flow >50 L/min for >1 hour, escalate respiratory support 4
- Contraindications: hypercapnia, hemodynamic instability, multi-organ failure, altered mental status 4
Noninvasive Ventilation (NIV):
- May combine HFNC with intermittent short-term NIV (1-2 hours) to reduce work of breathing 4
- High failure rates in moderate-to-severe ARDS; intubate within 1 hour if no improvement 4, 1
- Avoid in hemodynamically unstable patients 4
Lung-Protective Mechanical Ventilation
Immediately implement lung-protective ventilation in all intubated ARDS patients with tidal volume 4-6 mL/kg predicted body weight, plateau pressure ≤30 cmH₂O, and higher PEEP strategy in moderate-to-severe ARDS. 5, 1, 6
Ventilator Settings:
- Tidal volume: 4-6 mL/kg predicted body weight (not actual body weight) 4, 5, 6
- Plateau pressure: <30 cmH₂O 4, 5, 6
- PEEP: Use higher PEEP strategy for moderate-severe ARDS (PaO₂/FiO₂ <200 mmHg) 5, 3
- Target SpO₂: No higher than 96% to avoid oxygen toxicity 5, 1
PEEP Optimization:
- Titrate PEEP to best respiratory system compliance or use advanced methods like esophageal manometry 7
- Avoid prolonged lung recruitment maneuvers in moderate-severe ARDS (strong recommendation) 5, 3
- Monitor driving pressure and mechanical power as potential drivers of ventilator-induced lung injury 7
Adjunctive Therapies for Severe ARDS
Prone Positioning (PaO₂/FiO₂ <100 mmHg):
Implement prone positioning for 12-16 hours daily in severe ARDS, as this intervention has demonstrated significant mortality reduction. 5, 1, 6
- Apply deep sedation and analgesia during prone positioning 4
- Continue daily until oxygenation improves 5
Neuromuscular Blocking Agents:
Consider cisatracurium infusion for 48 hours in early severe ARDS (PaO₂/FiO₂ <150 mmHg within first 48 hours of mechanical ventilation) to improve ventilator synchrony and reduce oxygen consumption. 4, 5, 3
- Do not use routinely in all moderate-severe ARDS 4
- Particularly beneficial when ventilator-patient dyssynchrony persists despite sedation 4
Corticosteroids:
Administer systemic corticosteroids for ARDS (conditional recommendation, moderate certainty), particularly in COVID-19 ARDS where mortality benefit is established. 5, 3
Fluid Management
Implement a conservative fluid management strategy to minimize pulmonary edema while maintaining adequate organ perfusion, avoiding fluid overload which worsens oxygenation and promotes right ventricular failure. 5, 1, 6
Specific Fluid Targets:
- Monitor fluid balance carefully and continuously 1
- Excessive fluid administration increases mortality 1
- In acute pancreatitis-associated ARDS, limit total crystalloid to <4000 mL in first 24 hours 3
Advanced Therapies for Refractory Hypoxemia
VV-ECMO Indications:
Consider venovenous ECMO in selected patients with severe ARDS (PaO₂/FiO₂ <100 mmHg) who fail conventional management despite optimized lung-protective ventilation, prone positioning, and neuromuscular blockade. 5, 1, 7
- Only implement at centers with ECMO expertise 4
- Blood pumped from femoral vein, returns to right atrium through internal jugular vein after membrane oxygenation 4
- Particularly for patients with reversible disease 1
Inhaled Pulmonary Vasodilators:
Consider a trial of inhaled pulmonary vasodilators (inhaled nitric oxide or prostacyclin) as rescue therapy for severe hypoxemia, but discontinue immediately if no rapid improvement in oxygenation occurs. 5, 1
- Do not use inhaled nitric oxide routinely 5
Monitoring Requirements
Continuously monitor oxygen saturation, respiratory mechanics (plateau pressure, driving pressure, compliance), hemodynamics, and right ventricular function via echocardiography to detect acute cor pulmonale. 5, 1, 3
Specific Monitoring Parameters:
- Maintain arterial saturation >95% 3
- Assess for ventilator-patient dyssynchrony 4
- Monitor for barotrauma, especially with PEEP >10 cmH₂O in COVID-19 patients 5
- Use echocardiography to assess RV function and detect cor pulmonale 5, 3
Weaning from Mechanical Ventilation
Perform daily spontaneous breathing trials once the patient's condition improves (improved oxygenation, resolving underlying illness, hemodynamic stability), as this consistently reduces duration of mechanical ventilation. 1
- Consider noninvasive ventilation after extubation for high-risk patients to reduce ICU length of stay and mortality 1
- Close monitoring required during weaning process 1
Critical Pitfalls to Avoid
- Do not delay prone positioning in severe ARDS (PaO₂/FiO₂ <100 mmHg) 3
- Do not use high tidal volumes (>6 mL/kg PBW) or allow plateau pressures >30 cmH₂O 6
- Do not perform prolonged recruitment maneuvers in moderate-severe ARDS 5, 3
- Do not allow emergent intubation when deterioration is predictable; intubate early in controlled setting 1
- Do not overload with fluids, which worsens pulmonary edema and outcomes 1, 3
- Do not underutilize evidence-based strategies like prone positioning and lung-protective ventilation 3