Acute respiratory distress syndrome

Acute respiratory distress syndrome (ARDS) is a life-threatening inflammation with oedema in the lungs which leads to severe respiratory failure. It occurs in approx. 10% of ICU patients, and there is a 50% mortality rate.

Etiology

• Sepsis (most common)
• Pneumonia
• Aspiration of gastric content
• Shock
• Acute pancreatitis
• Major trauma

Clinical features

• Dyspnoea, restlessness, anxiety
• Altered mental status
• Cyanosis

Diagnosis and evaluation

Diagnosis by the Berlin criteria. All four must be met:

1. Respiratory failure within one week of a known cause of ARDS
2. Bilateral opacities on x-ray or CT
3. Hypoxaemia (decreased PaO2/FiO2)
   1. The degree of hypoxaemia determines whether it’s mild, moderate, or severe ARDS
4. Heart failure or fluid overload does not account for the respiratory failure

Management

• Treat the underlying condition
• Supportive oxygen therapy (non-invasive ventilation)
  • Non-invasive ventilation may be tried in mild-moderate ARDS, but 50% of patients require intubation later anyway
  • Intubation and invasive ventilation should not be delayed
• Lung-protective mechanical ventilation (invasive ventilation)
  • Lung-protective ventilation refers to changing the settings of the ventilator to protect the lung from barotrauma and volutrauma during invasive ventilation
  • This means low tidal volume, low plateau pressure, and high positive end-expiratory pressure (PEEP)
  • These settings cause hypercapnia but that’s not a problem and we allow it. This is called permissive hypercapnia
• Neuromuscular blockers if severe
  • Cisatracurium
  • Must be used early
• Prone positioning if moderate or severe
• Fluid overload should be avoided
• ECMO – if all other methods of oxygenation fail
• If due to COVID-19: Dexamethasone and tocilizumab