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Respiratory failure

Acute Respiratory Distress Syndrome (ARDS) & Acute Lung Injury (ALI)

Acute Respiratory Distress Syndrome (ARDS) is under diagnosed. Often the diagnosis is never changed from the underlying condition (pneumonia, aspiration, pancreatitis etc). The diagnostic criteria are listed in the table below.


Acute onset

Gas exchange abnormaility*

Bilateral infiltrates on CXR

Non-cardiogenic in origin

Known causative condition

Diagnostic criteria for ARDS/ALI.

*PaO2/FiO2 < 27 KPa for ARDS
PaO2/FiO2 < 40 KPa for ALI


It is the commonest cause of difficulty with ventilation in ICU. It is usually seen as part of a generalised inflammatory response with other organ dysfunction. If the lungs are the only failing organs, be suspicious of another cause of respiratory failure.

Treatment is based on the treatment of the underlying disease. Supportive therapy with ventilation allows time to treat the cause. Ventilation can worsen the inflammatory process and cause further deterioration unless care is taken to avoid ventilator induced lung injury. There are no specific treatments. Diuresis is reasonable, but often difficult to achieve without worsening other organ perfusion.

The underlying conditions that trigger ARDS can be either direct, if they affect the lungs (thoracic ARDS), or indirect (extrathoracic ARDS).



Inhalation or aspiration of toxic substances (e.g. smoke or gastric contents)




Sepsis of any cause



Profound/prolonged hypotension

Multiple transfusions


Sometimes both conditions are present, e.g. pneumonia and sepsis

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