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:
- Respiratory failure within one week of a known cause of ARDS
- Bilateral opacities on x-ray or CT
- Hypoxaemia (decreased PaO2/FiO2)
- The degree of hypoxaemia determines whether it’s mild, moderate, or severe ARDS
- 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