Acute respiratory distress syndrome (ARDS) is a severe form of lung disease. It is caused by various direct as well as indirect issues. Inflammation of the lung parenchyma leads to impaired gas exchange. Also systemic release of inflammatory mediators results in hypoxemia, inflammation and even multiple organ failure sometimes. This condition is usually fatal. It requires admission to an intensive care unit and mechanical ventilation.
Formerly ARDS signified ‘adult respiratory distress syndrome’ to differentiate it from ‘infant respiratory distress syndrome’. As this type of pulmonary disease also occurs in children, ARDS now stands for ‘acute’.
History of ARDS
Ashbaugh et al. first described ARDS in the year 1967. A controversy erupted over mortality and incidence as initially there was no clear definition. An expanded definition quantified it as physiologic respiratory impairment in 1988.
A new definition was proposed by the American-European Consensus Conference Committee in 1994. It had two advantages:
- Simple to use
- Recognizes that severity of pulmonary injury varies
ARDS was defined as the ratio of arterial partial oxygen tension(PaO2) as fraction of inspired oxygen (FiO2) below 200 mm Hg in the presence of bilateral alveolar infiltrates on the chest X-Rays.
A PaO2/FiO2 ratio less than 300 mm Hg with bilateral infiltrates indicates acute leg injury (ALI). It was formally considered to be different from ARDS. But it acts as a precursor to ARDS.
Diagnosis Of ARDS
ARDS can occur within 24-48 hours of an attack of acute illness or injury. In such cases, the patient experiences a shortness of breath, symptoms related to the underlying cause like shock and tachypnea.Long term illness like malaria can also trigger ARDS.
An chest X-ray and arterial blood gas analysis allows formal diagnosis. CT scans leads to more accurate images of the pulmonary parenchyma in ARDS than plain chest X-rays. But CT scans has little utility in the clinical management of ARDS patients. It remains largely as a research tool.
