12. Acute Respiratory Distress Syndrome (ARDS)

Definition

ARDS is a life-threatening, acute inflammatory lung injury causing non-cardiogenic pulmonary oedema, hypoxaemia, and reduced lung compliance.

🧪 Berlin Criteria (2012):

  • Acute onset within 1 week of insult

  • Bilateral infiltrates on CXR (not explained by effusion/collapse)

  • Hypoxaemia (PaO₂/FiO₂ ratio <300 mmHg)

  • No evidence of cardiac failure as cause (i.e., not cardiogenic)

🔬 Pathophysiology

🧠 Mnemonic: LEAKY LUNG

  • Lung injury → cytokine storm

  • Endothelial & alveolar damage

  • Alveoli fill with fluid (exudate)

  • Kapillary leak → ↓gas exchange

  • Yielding stiff, non-compliant lungs

  • Low compliance & poor oxygenation

  • Unresponsive to oxygen

  • Non-cardiogenic oedema

  • Generalised inflammation (e.g. sepsis, trauma)

🛡️Common Causes

🧠 Mnemonic: SPARTAS

  • Sepsis (most common)

  • Pancreatitis

  • Aspiration (gastric contents)

  • Road traffic accidents / trauma

  • Transfusions (TRALI)

  • Acute pneumonia

  • Smoke/toxic inhalation

Also: COVID-19, near drowning, drug overdose, massive transfusion.

📋Clinical Features

🧠 Mnemonic: ARDS

  • Acute onset dyspnoea

  • Respiratory failure (tachypnoea, cyanosis)

  • Decreased oxygen saturation despite oxygen therapy

  • Signs of underlying cause (sepsis, trauma, etc.)

🩺 Physical Examination Findings

  • Cyanosis

  • Tachypnoea

  • Bilateral crackles

  • Use of accessory muscles

  • Low oxygen saturations

  • Hypotension (if severe)

🔍 Investigations

🧠 Mnemonic: CXR ABG SEPSIS

  • CXR – bilateral pulmonary infiltrates (“white-out”)

  • ABG – PaO₂:FiO₂ ratio <300 mmHg

  • Bloods – FBC, U&E, LFT, CRP

  • Gram stain & cultures if infection

  • Sepsis screen (blood, urine, sputum)

  • Echo – to exclude cardiac failure

  • Procalcitonin (if sepsis suspected)

  • Serum albumin (low in sepsis, helps fluid balance)

  • Inflammatory markers (CRP, lactate)

  • Swab viral PCRs (e.g. COVID-19, influenza)

🧾 Management

🧠 Mnemonic: LOW TIDE

  • Low tidal volume ventilation (6 mL/kg) – lung-protective strategy

  • Oxygenation: target sats 92–96% (may need PEEP/CPAP)

  • Watch for fluid overload – cautious fluid balance

  • Treat underlying cause (e.g. sepsis, pneumonia)

  • Intubation + mechanical ventilation if severe

  • Diuretics (with caution) if pulmonary congestion

  • Escalate to ICU early

  • Prone positioning for severe ARDS

  • Consider ECMO in refractory cases (specialist centres)

⚠️ Complications

  • Respiratory failure → mechanical ventilation

  • Ventilator-associated pneumonia

  • Barotrauma (pneumothorax, pneumomediastinum)

  • Fibrosis

  • Multi-organ failure

  • High mortality (30–50%)

🧐 Differentials

🧠 Mnemonic: CHOPPED

  • Cardiogenic pulmonary oedema

  • Haemorrhage (alveolar)

  • Overload (fluid)

  • Pneumonia

  • Pulmonary embolism

  • Eosinophilic pneumonia

  • Drug reaction

📌 PARA Revision Tips

  • Know the Berlin Criteria

  • Recognise white-out CXR vs cardiogenic oedema

  • Management: focus on low tidal volume, oxygenation, and treating the cause

  • Understand sepsis as the most common trigger

  • High-yield for clinical interpretation + emergency OSCE

🔎 Last updated in line with NICE CG177 (2014) + Berlin Definition (2012)
Last reviewed: July 2025
🔒 PASSMAP ensures all content is NICE-aligned and reviewed for Physician Associate Registration Assessment (PARA) success.

Scroll to Top