Acute, diffuse, inflammatory lung injury with bilateral infiltrates and hypoxaemia not fully explained by cardiac failure. Berlin definition stratifies severity.
⚠ Red flags
- PaO₂/FiO₂ <100 despite optimised LPV
- Driving pressure >15 cmH₂O — poor prognosis
- Pneumothorax / barotrauma
- Refractory shock alongside ARDS
Diagnostic criteria
Clinical
- Onset within 1 week of known insult or new/worsening respiratory symptoms
- Respiratory failure not fully explained by cardiac failure or fluid overload
Investigations
- Bilateral opacities on CXR/CT not fully explained by effusion, collapse, or nodules
- PaO₂/FiO₂ ≤300 on PEEP ≥5 cmH₂O
Scoring tools
- Berlin severity (mild / moderate / severe)
- Murray Lung Injury Score
Investigations
Essential
- ABG with PaO₂/FiO₂ ratio
- CXR — bilateral infiltrates
- Echo to exclude cardiogenic pulmonary oedema
- Septic screen for precipitant
Optional
- CT thorax for atypical features
- Bronchoalveolar lavage if infection or interstitial process suspected
- Inflammatory markers, procalcitonin
Management
Acute
- Lung-protective ventilation: Vt 4–6 mL/kg IBW, plateau pressure ≤30 cmH₂O
- PEEP titration to optimise oxygenation; target SpO₂ 92–96%
- Conservative fluid strategy after initial resuscitation
- Prone positioning ≥16h/day for moderate-to-severe ARDS (PaO₂/FiO₂ <150)
- Neuromuscular blockade (cisatracurium) considered in severe ARDS during first 48h
- VV-ECMO referral if refractory hypoxaemia despite optimal LPV
Long-term
- Daily SAT/SBT protocol once stabilised
- Early mobilisation and ICU rehabilitation
- Post-ICU follow-up at 3 months — physical, psychological, cognitive
Non-pharmacological
- Treat underlying cause (sepsis source control, antibiotics for pneumonia)
- DVT and stress ulcer prophylaxis
- Nutritional support — enteral when possible
Pharmacological
| Drug | Dose | Notes |
|---|---|---|
| Cisatracurium | 0.15 mg/kg IV bolus then 1–3 µg/kg/min infusion | First 48h of severe ARDS to reduce ventilator dyssynchrony. |
| Dexamethasone | 20 mg IV daily for 5 days, then 10 mg for 5 days | Consider in moderate-severe ARDS (DEXA-ARDS); standard in COVID-related ARDS. |
| Inhaled nitric oxide | 5–20 ppm | Rescue therapy for refractory hypoxaemia; transient improvement only. |
Monitoring
- Hourly ABG / SpO₂ during instability
- Daily PaO₂/FiO₂ ratio and driving pressure
- Daily SBT/SAT, sedation interruption
- Cumulative fluid balance
Referral criteria
- All ARDS — ICU level care
- ECMO centre referral if PaO₂/FiO₂ <80 despite optimal therapy or pH <7.20 from hypercapnia
Complications
- Refractory hypoxaemia
- Ventilator-induced lung injury (VILI), pneumothorax
- ICU-acquired weakness
- Pulmonary fibrosis (long-term)
- Cognitive and psychological sequelae
Special populations
- Pregnancy
- Same LPV principles; engage obstetrics — delivery may improve maternal oxygenation in late pregnancy.
- Renal impairment
- Strict fluid balance even more critical; coordinate RRT for fluid removal.
- Hepatic impairment
- Avoid hepatotoxic drugs; hepatorenal coexistence increases mortality.
- Elderly
- Frailty informs ECMO and prolonged ventilation decisions; involve family early.
- Paediatric
- Use PALICC criteria (oxygenation index) for paediatric ARDS; weight-based settings.