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Acute Respiratory Distress Syndrome

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Overview

Acute respiratory distress syndrome (ARDS) is characterised by sudden-onset widespread inflammation of the lungs leading to non-cardiogenic pulmonary oedema (oedema of the lungs secondary to acute damage to the alveoli, and not heart failure).

The inflammation leads to increased capillary permeability within the lungs, allowing fluid to leak out, leading to oedema.

Risk Factors

Presentation

Features may be:

Differential Diagnoses

Acute heart failure

  • Chest X-rays may show cardiomegaly
  • There may be an elevated NT-proBNP
  • There may be a history of cardiac disease
  • Examination may reveal an S3 or elevated jugular venous pressure (JVP)

Investigations

All patients

  • Chest x-ray:
    • Show bilateral infiltrates
  • Arterial blood gases:
    • PaO2/FiO2 (fraction of inspired oxygen) ratio ≤300
  • Pulmonary capillary wedge pressure:
    • If there is diagnostic doubt, this can be performed to exclude a cardiogenic cause for the pulmonary oedema
    • In ARDS, the pulmonary capillary wedge pressure is not elevated

Diagnosis

Berlin definition

ARDS is diagnosed in an individual with a predisposing factor if the following are met:

  • Onset within 1 week of known clinical insult or new/worsening respiratory symptoms
  • Bilateral opacities seen on chest x-ray not explained by another condition
  • The pulmonary oedema is non-cardiogenic (use pulmonary capillary wedge pressure if in doubt)
  • PaO2/FiO2 (fraction of inspired oxygen) ratio ≤300

Management

Overview

  • 1st-line: admit to ITU + manage underlying cause + supportive therapy
  • Intubation and ventilation may need to be considered

Complications

  • Multiple organ failure
  • Persistent dyspnoea
  • Persisting restrictive or obstructive lung disease
  • Death

Prognosis

  • The mortality rate can be as high as 30%

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