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Acute Respiratory Distress Syndrome (ARDS)


Bhakti K. Patel

, MD, University of Chicago

Reviewed/Revised Apr 2022 | Modified Sep 2022
Topic Resources

Acute respiratory distress syndrome is a type of respiratory (lung) failure Respiratory Failure Respiratory failure is a condition in which the level of oxygen in the blood becomes dangerously low or the level of carbon dioxide in the blood becomes dangerously high. Conditions that block... read more resulting from many different disorders that cause fluid to accumulate in the lungs and oxygen levels in the blood to be too low.

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

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 Atelectasis Atelectasis is a condition in which all or part of a lung becomes airless and collapses. Blockage of the bronchial tubes is a common cause of atelectasis. Shortness of breath can develop if... read more ) 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 Causes Respiratory failure is a condition in which the level of oxygen in the blood becomes dangerously low or the level of carbon dioxide in the blood becomes dangerously high. Conditions that block... read more .

The Alveoli

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 White Blood Cells The main components of blood include Plasma Red blood cells White blood cells Platelets read more 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 Hospital-Acquired Pneumonia Hospital-acquired pneumonia is lung infection that develops in people who have been hospitalized, typically after about 2 days or more of hospitalization. Many bacteria, viruses, and even fungi... read more .

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 Cyanosis Cyanosis is a bluish or grayish discoloration of the skin resulting from an inadequate amount of oxygen in the blood. Cyanosis occurs when oxygen-depleted (deoxygenated) blood, which is bluish... read more ) 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 Overview of Abnormal Heart Rhythms Abnormal heart rhythms (arrhythmias) are sequences of heartbeats that are irregular, too fast, too slow, or conducted via an abnormal electrical pathway through the heart. Heart disorders are... read more Overview of 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 Pulse oximetry Both arterial blood gas testing and pulse oximetry measure the amount of oxygen in the blood, which helps determine how well the lungs are functioning. Arterial blood gas tests are invasive... read more . The level of oxygen (along with carbon dioxide) in the blood can also be measured by analyzing a blood sample taken from an artery.

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.

Treatment of ARDS

  • Treatment of the cause

  • Oxygen therapy

  • Often mechanical ventilation

Successful treatment usually depends on treating the underlying disorder (for example, pneumonia). Oxygen therapy Oxygen Therapy Oxygen therapy is a treatment that delivers extra oxygen to the lungs when the level of oxygen in the blood is too low. Oxygen is a gas that makes up about 21% of the air we breathe. The lungs... read more 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 Mechanical Ventilation Mechanical ventilation is use of a machine to aid the movement of air into and out of the lungs. Some people with respiratory failure need a mechanical ventilator (a machine that helps air get... read more must be used. Usually a ventilator delivers oxygen-rich air under pressure using a tube inserted through the mouth into the windpipe (trachea).

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