Acute respiratory distress syndrome is a type of respiratory (lung) failure resulting from many different disorders that cause fluid to accumulate in the lungs and oxygen levels in the blood to be too low.
The person has shortness of breath, usually with rapid, shallow breathing, the skin may become mottled or blue (cyanosis), and other organs such as the heart and brain may malfunction.
A fingertip sensor (pulse oximetry) or a sample of blood from an artery is used to determine the levels of oxygen in the blood, and a chest x-ray is also taken.
People are treated in an intensive care unit because they may need mechanical ventilation.
Oxygen is given and the cause of the respiratory failure is treated.
Acute respiratory distress syndrome (ARDS) is a medical emergency. It may occur in people who already have lung disease or in those with previously normal lungs. This disorder used to be called adult respiratory distress syndrome, although it can occur in children.
ARDS is divided into three categories: mild, moderate, and severe. The category is determined by comparing the level of oxygen in the blood with the amount of oxygen that needs to be given to achieve that level.
Causes of ARDS
Any disease or condition that injures the lungs can cause ARDS. More than half of the people with ARDS develop it as a consequence of a severe, widespread infection (sepsis) or pneumonia. Some other causes include
Aspiration (inhalation) of acidic stomach contents into the lungs
Certain complications of pregnancy (such as amniotic fluid embolism, preeclampsia, infection of tissues in the uterus before, during, or after a miscarriage [septic abortion], and others)
Chest injury (pulmonary contusion)
Inflammation of the pancreas (pancreatitis)
Inhalation of large amounts of smoke
Inhalation of other toxic gas
Injury to the lungs due to inhaling high concentrations of oxygen
Life-threatening or severe injuries
Overdose of certain drugs, such as heroin, methadone, propoxyphene, or aspirin
Prolonged or severe low blood pressure (shock)
Severe, widespread infection (sepsis)
Transfusions of more than about 15 units of blood in a short period of time
When the small air sacs (alveoli) and tiny blood vessels (capillaries) of the lungs are injured, blood and fluid leak into the spaces between the air sacs and eventually into the sacs themselves. Collapse of many alveoli (a condition called atelectasis) may also result because of a reduction in surfactant, a liquid that coats the inside surface of the alveoli and helps to keep them open.
Fluid in the alveoli and the collapse of many alveoli interfere with the movement of oxygen from inhaled air into the blood. Thus, the level of oxygen in the blood decreases sharply. Movement of carbon dioxide from the blood to air that is exhaled is affected less, and the level of carbon dioxide in the blood changes very little. Because respiratory failure in ARDS results mainly from low levels of oxygen, it is considered hypoxemic respiratory failure.
The decrease in the level of oxygen in the blood caused by ARDS and the leakage into the bloodstream of certain proteins (cytokines) produced by injured lung cells and white blood cells can lead to inflammation and complications in other organs. Failure of several organs (a condition called multiple organ system failure) may also result. Organ failure can begin soon after the start of ARDS or days or weeks later. Additionally, people with ARDS are less able to fight lung infections, and they tend to develop bacterial pneumonia.
Symptoms of ARDS
ARDS usually develops within 24 to 48 hours of the original injury or disease but may take as long as 4 or 5 days to occur. The person first has shortness of breath, usually with rapid, shallow breathing.
Using a stethoscope, a doctor may hear crackling or wheezing sounds in the lungs. The skin may become mottled or blue (cyanosis) in light-skinned people and gray or whitish coloration in the mouth, around the eyes, and under the nails in dark-skinned people because of low oxygen levels in the blood. Other organs such as the heart and brain may malfunction, resulting in a rapid heart rate, abnormal heart rhythms (arrhythmias), confusion, and sleepiness.
Diagnosis of ARDS
Measurements of the levels of oxygen in the blood
Chest x-ray
The level of oxygen in the blood can be measured without taking a blood sample by using a sensor placed on a finger or an earlobe—a procedure called pulse oximetry. The level of oxygen (along with carbon dioxide) in the blood can also be measured by analyzing a blood sample taken from an artery.
Chest x-rays show fluid in spaces that should be filled with air. Further tests may be needed to ensure that heart failure is not the cause of the problem.
Prognosis of ARDS
Without prompt treatment, many people who have ARDS will not survive. However, depending upon the underlying disorder, with appropriate treatment, about 60 to 75% of people with ARDS survive.
People who respond promptly to treatment usually recover completely with few or no long-term lung abnormalities. Those whose treatment involves long periods on a ventilator (a machine that helps air get in and out of the lungs) are more likely to develop lung scarring. Such scarring may decrease over a few months after the person is taken off the ventilator. Lung scarring, if extensive, can impair lung function permanently in ways that are noticeable during certain day-to-day activities. Less extensive scarring may impair lung function only when the lungs are stressed, such as during exercise or an illness.
Many people lose large amounts of weight and muscle during the illness. Rehabilitation in the hospital can help them regain their strength and independence.
Treatment of ARDS
Treatment of the cause
Oxygen therapy
Often mechanical ventilation
People with ARDS are treated in an intensive care unit (ICU).
Successful treatment usually depends on treating the underlying disorder (for example, pneumonia). Oxygen therapy, which is vital to correcting low oxygen levels, also is given.
If oxygen delivered by a face mask or other device (such as a helmet or nasal prongs) does not correct the low blood oxygen levels, or if very high doses of inhaled oxygen are required, mechanical ventilation must be used. Usually a ventilator delivers oxygen-rich air under pressure using a tube inserted through the mouth into the windpipe (trachea).
