In ARDS there is respiratory failure of sudden (acute) onset due to the rapid accumulation of fluid in the lungs (pulmonary edema) following an abrupt increase in the permeability of the normal barrier between the capillaries and the air sacs in the lungs. ARDS is the most serious response to acute lung injury.
The types of acute lung injury that may lead to ARDS are very diverse. They include (but are by no means limited to) aspiration (swallowing fluid or food down the windpipe), inhalation of a toxic substance, widespread (diffuse) infection of the lungs, sepsis (blood infection) and near drowning.
ARDS forces the muscles of the lungs to work harder causing labored breathing (huffing and puffing). Despite the effort, breathing is inefficient. There is hypoxemia (an abnormally low level of oxygen in the blood), a characteristic feature of ARDS.
The treatment of ARDS frequently involves the transient use of a mechanical ventilator to help breathing.