Diagnosis and Management of ARDS
Diagnostic Criteria
Diagnose ARDS using the Berlin Definition: acute onset (within 1 week of known insult), bilateral pulmonary opacities on chest imaging not fully explained by effusions/nodules/collapse, PaO₂/FiO₂ ≤300 mmHg with minimum PEEP of 5 cmH₂O, and respiratory failure not fully explained by cardiac failure or fluid overload. 1
Severity Classification by PaO₂/FiO₂ Ratio:
Key Diagnostic Considerations:
- The Berlin definition has significantly greater predictive validity for mortality than prior definitions 3
- Clinician interpretation of edema origin and chest radiograph findings may be less reliable, contributing to underrecognition 3
- ARDS must be differentiated from pneumonia and congestive heart failure; look specifically for absence of fluid overload signs 4
Initial Respiratory Support Strategy
For Mild ARDS (PaO₂/FiO₂ 200-300 mmHg):
- Consider high-flow nasal cannula (HFNC) at 30-40 L/min with FiO₂ 50-60% only in hemodynamically stable, alert, cooperative patients without pneumonia as the cause and SAPS II score <34 1
- Escalate to intubation if FiO₂ >70% and flow >50 L/min for >1 hour, or if Rapid Shallow Breathing Index >105 breaths/min/L 1
- Perform arterial blood gas analysis at 1-2 hours and again at 4-6 hours if minimal improvement 1
Absolute Contraindications to Non-Invasive Support:
- Impaired consciousness or inability to protect airway 1
- Hemodynamic instability 1
- Copious respiratory secretions 1
- Multi-organ failure 1
For Moderate to Severe ARDS:
- Proceed directly to early intubation in a controlled setting rather than attempting non-invasive ventilation 1
Lung-Protective Mechanical Ventilation (Mandatory for All Intubated Patients)
Immediately implement lung-protective ventilation with tidal volume 4-8 mL/kg predicted body weight and plateau pressure ≤30 cmH₂O—this is the only intervention proven to reduce mortality in ARDS and represents a strong recommendation suitable as a performance measure. 2, 5, 1
Specific Ventilator Settings:
- Tidal volume: 4-8 mL/kg predicted body weight (not actual body weight) 2, 5
- Plateau pressure: ≤30 cmH₂O 2, 5
- Target SpO₂: No higher than 96% to avoid oxygen toxicity 6, 1
- Monitor driving pressure as a key parameter to minimize ventilator-induced lung injury 7
PEEP Strategy Based on Severity:
- For moderate to severe ARDS (PaO₂/FiO₂ <200 mmHg): Use higher PEEP strategy without prolonged lung recruitment maneuvers 2, 6
- Higher PEEP reduces mortality and improves oxygenation 5
- Strongly avoid prolonged lung recruitment maneuvers due to high probability of hemodynamic harm and no mortality benefit 2, 5, 6
Adjunctive Therapies for Severe ARDS (PaO₂/FiO₂ <100 mmHg)
Prone Positioning (Strong Evidence):
Implement prone positioning for >12 hours daily (12-16 hours) in severe ARDS—this is a performance measure with proven mortality reduction. 5, 6, 1
- Apply deep sedation and analgesia during prone positioning 1
- This intervention has demonstrated significant mortality benefit in patients with PaO₂/FiO₂ <150 mmHg 3
Neuromuscular Blocking Agents:
- Use neuromuscular blockers (cisatracurium infusion for 48 hours) in early severe ARDS to improve ventilator synchrony and reduce oxygen consumption 2, 6, 1
- Particularly beneficial when ventilator-patient dyssynchrony persists despite sedation 1
- This is a conditional recommendation with low certainty of evidence 2
Systemic Corticosteroids:
Administer systemic corticosteroids for ARDS—this represents a conditional recommendation with moderate certainty of evidence from the 2024 American Thoracic Society guidelines. 2, 5, 6
- Appropriate timely use may reduce mortality 8
Fluid Management Strategy
Implement conservative fluid management to minimize pulmonary edema while maintaining adequate organ perfusion. 6, 1
Specific Fluid Targets:
- Limit total crystalloid to <4000 mL in first 24 hours 5
- Use non-aggressive resuscitation at 1.5 mL/kg/hr after initial 10 mL/kg bolus 5
- Monitor fluid balance carefully—excessive fluid administration worsens oxygenation, promotes right ventricular failure, and increases mortality 1
Advanced Rescue Therapies for Refractory Hypoxemia
Venovenous ECMO:
Consider VV-ECMO in selected patients with severe ARDS (PaO₂/FiO₂ <100 mmHg) who fail conventional management, particularly those with reversible disease. 2, 6, 1
- This is a conditional recommendation with low certainty of evidence 2
- Should only be implemented at centers with ECMO expertise 1
- Blood is pumped from femoral vein and returns to right atrium through internal jugular vein after membrane oxygenation 1
Inhaled Pulmonary Vasodilators:
- Consider a trial of inhaled pulmonary vasodilators (inhaled nitric oxide or prostaglandins) as rescue therapy for severe hypoxemia 6, 1
- Discontinue if no rapid improvement in oxygenation 6, 1
- These confer short-term improvement without proven survival benefit 8
Monitoring Requirements
Continuous Monitoring:
- Oxygen saturation 6, 1
- Respiratory mechanics (plateau pressure, driving pressure, PEEP) 6, 1
- Hemodynamics 6, 1
- Assess for ventilator-patient dyssynchrony 1
Echocardiography:
- Use echocardiography to assess right ventricular function and detect acute cor pulmonale in severe cases 5, 6, 1
Barotrauma Surveillance:
Ventilator Weaning
Daily Assessment:
- Perform daily spontaneous breathing trials once the patient's condition improves—this consistently reduces duration of mechanical ventilation 1
- Use noninvasive ventilation after extubation for patients at high risk for extubation failure to reduce ICU length of stay and mortality 1
Critical Pitfalls to Avoid
Most Common Errors Leading to Increased Mortality:
- Underutilization of lung-protective ventilation and prone positioning 5
- Aggressive fluid resuscitation worsening pulmonary edema 5
- Delaying prone positioning in severe ARDS 5
- Using prolonged lung recruitment maneuvers with high PEEP 2, 5, 6
- Allowing tidal volumes >8 mL/kg predicted body weight 2, 9
- Delaying intubation in deteriorating patients on non-invasive support 1