What causes adult respiratory distress syndrome (ARDS)?ARDS is a medical emergency. It can be caused by any major lung inflammation or injury. Some common causes include pneumonia, septic shock, trauma, aspiration of vomit, or chemical inhalation.
ARDS develops as inflammation and injury to the lung and causes a buildup of fluid in the air sacs. This fluid inhibits the passage of oxygen from the air into the bloodstream. The fluid buildup also makes the lungs heavy and stiff, and the lungs' ability to expand is severely decreased.
Blood concentration of oxygen can remain dangerously low in spite of supplemental oxygen delivered by a mechanical ventilator (breathing machine) through an endotracheal tube (breathing tube). Tiny air sacs called alveoli are located at the tips of the body’s smallest breathing tubes, called the bronchi. The alveoli are responsible for passing oxygen into the blood. When the lungs are injured by infection or disease, blood and fluid begin to leak into the alveoli. When this happens, oxygen can’t enter the alveoli, which means oxygen is no longer getting into the blood. Because the lungs are inflamed and filled with fluid, the patient finds it increasingly difficult to breathe. The inflammation in the lungs leads to scarring, which is called fibrosis. The lungs eventually become stiff with scar tissue and breathing becomes very difficult.
In ARDS, the injured lung is believed to go through three phases: exudative, proliferative, and fibrotic, but the course of each phase and the overall disease progression is variable. In the exudative phase, damage to the alveolar epithelium and vascular endothelium produces leakage of water, protein, and inflammatory and red blood cells into the interstitium and alveolar lumen. These changes are induced by a complex interplay of proinflammatory and anti-inflammatory mediators.
There are many possible causes of the type of lung injury that leads to ARDS. These include inhaling high concentrations of smoke, toxins, or oxygen; severe burns; blood infection (sepsis); pneumonia; pancreatitis; trauma to other parts of the body; or drug overdose. Fluids can also get into the lungs and cause injury when they are breathed in (aspirated), such as in a near drowning or when a person who is unconscious vomits.
Typically patients require care in an intensive care unit (ICU). Symptoms usually develop within 24 to 48 hours of the original injury or illness. ARDS often occurs along with the failure of other organ systems, such as the liver or the kidneys. Cigarette smoking may be a risk factor.