What is the immediate treatment for a patient diagnosed with Acute Respiratory Distress Syndrome (ARDS)?

Diagnosis and Immediate Treatment of Acute Respiratory Distress Syndrome (ARDS)

Diagnostic Criteria

Diagnose ARDS using the Berlin Definition: acute onset (within 1 week of known insult), bilateral pulmonary opacities on chest imaging not explained by cardiac failure or fluid overload, and PaO₂/FiO₂ ≤300 mmHg with minimum PEEP of 5 cmH₂O. 1, 2 Classify severity immediately: mild (PaO₂/FiO₂ 200-300 mmHg), moderate (100-200 mmHg), or severe (<100 mmHg). 1, 3

Immediate Respiratory Support Algorithm

For Mild ARDS (PaO₂/FiO₂ 200-300 mmHg):

• Consider high-flow nasal cannula (30-40 L/min, FiO₂ 50-60%) with close monitoring for 1 hour maximum. 2 If FiO₂ >70% and flow >50 L/min for >1 hour, or if deterioration occurs, proceed immediately to intubation. 2
• Contraindications to noninvasive support: hypercapnia, hemodynamic instability, multi-organ failure, or altered mental status. 2

For Moderate-to-Severe ARDS (PaO₂/FiO₂ <200 mmHg):

• Proceed directly to intubation in a controlled setting—do not delay with noninvasive ventilation. 2 Failure rates are high in this population, and emergent intubation carries worse outcomes. 2

Lung-Protective Mechanical Ventilation (Initiate Immediately Upon Intubation)

Set tidal volume at 6 mL/kg predicted body weight (acceptable range 4-8 mL/kg PBW) and maintain plateau pressure <30 cmH₂O—this is the only ventilation strategy proven to reduce mortality. 1, 3, 4

Calculate Predicted Body Weight:

• Males: 50 + 0.91 × [height (cm) - 152.4] kg 3
• Females: 45.5 + 0.91 × [height (cm) - 152.4] kg 3

PEEP Titration Strategy:

• For moderate-to-severe ARDS (PaO₂/FiO₂ <200 mmHg): Use higher PEEP (typically >10 cmH₂O). 1, 3 This improves oxygenation and reduces atelectotrauma. 1
• For mild ARDS (PaO₂/FiO₂ 200-300 mmHg): Lower PEEP may be appropriate. 3
• Monitor for barotrauma when PEEP >10 cmH₂O and reduce PEEP if hemodynamic instability develops. 3

Permissive Hypercapnia:

• Accept elevated PaCO₂ and pH >7.20 as a consequence of lung protection—do not prioritize normocapnia over protective ventilation. 3 Consider sodium bicarbonate infusion if pH falls below this threshold. 1

Oxygenation Targets:

• Target SpO₂ 88-95% to avoid oxygen toxicity while maintaining adequate tissue oxygenation. 3, 2 Do not exceed SpO₂ 96%. 2

Adjunctive Therapies Based on Severity

For Severe ARDS (PaO₂/FiO₂ <150 mmHg):

Implement prone positioning for at least 12-16 hours daily—this reduces mortality (RR 0.74) and should not be delayed. 1, 3 Trials demonstrating benefit used >12 hours/day; shorter durations showed no mortality improvement. 3

Consider neuromuscular blocking agents for up to 48 hours in early severe ARDS. 1, 3 Administer as intermittent boluses when possible; use continuous infusion only for persistent ventilator dyssynchrony, need for deep sedation during prone positioning, or persistently high plateau pressures. 3, 2

Administer systemic corticosteroids to mechanically ventilated ARDS patients. 1, 3 This represents the most recent high-quality guideline recommendation (2024 American Thoracic Society, conditional recommendation with moderate certainty). 1 Avoid doses exceeding methylprednisolone 1-2 mg/kg/day equivalent for 3-5 days. 1

Fluid Management

Implement conservative fluid strategy in established ARDS without tissue hypoperfusion. 3, 2 This improves ventilator-free days without increasing non-pulmonary organ failures. 3 Monitor fluid balance carefully—excessive fluid worsens oxygenation, promotes right ventricular failure, and increases mortality. 2

Rescue Therapies for Refractory Hypoxemia

When Standard Therapies Fail:

For severe refractory ARDS (lung injury score >3 or pH <7.2 from uncompensated hypercapnia) despite optimized ventilation, proning, and adjunctive therapies, consider VV-ECMO only at experienced centers. 1, 3 This is resource-intensive and should be reserved for carefully selected patients with reversible disease. 3, 2

Consider inhaled pulmonary vasodilators as rescue therapy, but discontinue if no rapid improvement in oxygenation occurs. 2

Critical Interventions to AVOID

Do not use high-frequency oscillatory ventilation—this is strongly recommended against and may be harmful. 1 It may still be considered as last-resort rescue therapy in severe refractory cases. 1

Do not use prolonged lung recruitment maneuvers—these are associated with harm (strong recommendation, moderate certainty). 1, 3 Brief recruitment maneuvers may be considered in severe refractory hypoxemia with close monitoring for hypotension or desaturation. 1

Do not routinely use pulmonary artery catheters, β-2 agonists (unless bronchospasm present), or omega-3 fatty acid supplementation. 1, 3

Monitoring Requirements

• Continuously monitor SpO₂, respiratory mechanics (plateau pressure, driving pressure, PEEP), and hemodynamics. 2
• Perform echocardiography to assess right ventricular function and detect acute cor pulmonale. 2
• Assess for ventilator-patient dyssynchrony. 2

Weaning Strategy

Perform daily spontaneous breathing trials once the patient's condition improves (improved oxygenation, hemodynamic stability, resolution of underlying insult). 2 This consistently reduces duration of mechanical ventilation. 2, 4

Minimize continuous sedation, targeting specific endpoints to facilitate weaning. 3 Consider noninvasive ventilation after extubation for high-risk patients. 2

Common Pitfalls

• Do not use tidal volumes >8 mL/kg PBW even if plateau pressures are acceptable—both parameters must be optimized. 3
• Do not delay prone positioning in severe ARDS—early implementation improves outcomes. 3
• Do not apply higher PEEP indiscriminately—tailor to ARDS severity and hemodynamic tolerance. 3 While higher PEEP benefits moderate-to-severe ARDS, one large trial showed no mortality difference between higher and lower PEEP strategies when both used lung-protective ventilation. 5
• Do not underutilize evidence-based strategies—prone positioning and lung-protective ventilation remain underused despite proven mortality benefit. 1

Supportive Care

Provide stress ulcer prophylaxis, venous thromboembolism prophylaxis, blood glucose control, and enteral nutrition when tolerated. 1 Maintain head of bed elevation 30-45 degrees to prevent ventilator-associated pneumonia. 1 Treat underlying cause (pneumonia, sepsis) with appropriate empirical antibiotics, avoiding blind broad-spectrum combinations. 1