ARDS - Acute Respiratory Distress Syndrome


What is ARDS?


Classified as non-cardiogenic pulmonary oedema

It typically presents within one week of injury

The term 'acute lung injury' has been discontinued in favour of ARDS

It results from bilateral infiltrates in the lung that leads to increased vascular permeability, increased lung dead space and reduced lung compliance, resulting in hypoxaemia


What are the causes?


Infection: pneumonia, aspiration pneumonia

Trauma: massive trauma, inhalation injury, drowning

Other: pancreatitis, transfusion injury, embolism


Why does it matter?


The LUNGSAFE trial identified around 10% of ICU admissions showed ARDS. Despite this the condition is underrecognised by professionals and therefore undertreated

There is a high mortality rate associated with ARDS, increasing with the severity


How is it diagnosed?


CXR - shows bilateral alveolar shadowing

Refractory hypoxaemia: Work out the PaO2:FiO2 ratio

  • In a healthy individual on air the FiO2 will be 21%, the PaO2 between 11-14. Therefore a normal PaO2:FiO2 ratio will be 14/21= 0.66= 66%
  • Stage 1 ARDS is classified by a ratio of <45% (27% mortality)
  • Stage 2 is <30% (32% mortality)
  • Stage 3 is <15% (45% mortality)


How is it treated?


Treat the underlying cause

Position the patient  - the prone position improves oxygenation and mortality in ARDS

Use PEEP - set a tidal volume of 6ml/kg of predicted body weight. Set the respiratory rate to maintain optimal mechanical ventilation (not greater than 35 resps per minute). Target sats >90%

Get ITU involvement early




High mortality

Good outcome at 6 months for survivors

May suffer from a reduced quality of life due to hypoxia induced cognitive impairment, depression and PTSD




Epidemiology, Patterns of Care, and Mortality for Patients With Acute Respiratory Distress Syndrome in Intensive Care Units in 50 Countries. Giacomo Bellani, MD, PhD1,2; John G. Laffey, MD, MA3,4; Tài Pham, MD5,6,7; et al;  the LUNG SAFE Investigators and the ESICM Trials Group. JAMA. 2016;315(8):788-800. doi:10.1001/jama.2016.0291