The signs and symptoms of ARDS can vary in intensity, depending on its cause and severity, as well as the presence of underlying heart or lung disease. They include:

• Severe shortness of breath
• Labored and unusually rapid breathing
• Low blood pressure
• Confusion and extreme tiredness

The mechanical cause of ARDS is fluid leaked from the smallest blood vessels in the lungs into the tiny air sacs where blood is oxygenated. Normally, a protective membrane keeps this fluid in the vessels. Severe illness or injury, however, can cause damage to the membrane, leading to the fluid leakage of ARDS.

The most common underlying causes of ARDS include:

• Sepsis. The most common cause of ARDS is sepsis, a serious and widespread infection of the bloodstream.
• Inhalation of harmful substances. Breathing high concentrations of smoke or chemical fumes can result in ARDS, as can inhaling (aspirating) vomit or near-drowning episodes.
• Severe pneumonia. Severe cases of pneumonia usually affect all five lobes of the lungs.
• Head, chest or other major injury. Accidents, such as falls or car crashes, can directly damage the lungs or the portion of the brain that controls breathing.
• Others. Pancreatitis (inflammation of the pancreas), massive blood transfusions and burns.

Most people who develop ARDS are already hospitalized for another condition, and many are critically ill. You're especially at risk if you have a widespread infection in your bloodstream (sepsis).

People who have a history of chronic alcoholism are at higher risk of developing ARDS. They're also more likely to die of ARDS.

If you have ARDS, you can develop other medical problems while in the hospital. The most common problems are:

• Blood clots. Lying still in the hospital while you're on a ventilator can increase your risk of developing blood clots, particularly in the deep veins in your legs. If a clot forms in your leg, a portion of it can break off and travel to one or both of your lungs (pulmonary embolism) — where it blocks blood flow.
• Collapsed lung (pneumothorax). In most ARDS cases, a breathing machine called a ventilator is used to increase oxygen in the body and force fluid out of the lungs. However, the pressure and air volume of the ventilator can force gas to go through a small hole in the very outside of a lung and cause that lung to collapse.
• Infections. Because the ventilator is attached directly to a tube inserted in your windpipe, this makes it much easier for germs to infect and further injure your lungs.
• Scarring (pulmonary fibrosis). Scarring and thickening of the tissue between the air sacs can occur within a few weeks of the onset of ARDS. This stiffens your lungs, making it even more difficult for oxygen to flow from the air sacs into your bloodstream.