acute respiratory distress syndrome (ARDS)
A normal alveolus (left) and a damaged injured alveolus in the acute phase of acute respiratory distress syndrome (right).
Acute respiratory distress syndrome (ARDS) is breathing failure that can occur in critically ill persons with underlying illnesses. It is not a specific disease. Instead, it is a life-threatening condition that occurs when there is severe fluid buildup in both lungs. The fluid buildup prevents the lungs from working properly – that is, allowing the transfer of oxygen from air into the body and carbon dioxide out of the body into the air.
In ARDS, the capillaries (tiny blood vessels) in the alveoli of the lungs are damaged because of an infection, injury, blood loss, or inhalation injury. Fluid leaks from the blood vessels into the alveoli. While some alveoli fill with fluid, others collapse. When this happens, the lungs can no longer fill properly with air and they become stiff. Without air entering the lungs properly, the amount of oxygen in the blood drops. When this happens, the person with ARDS must be given extra oxygen and may need the help of a breathing machine.
Breathing failure can occur very quickly after the condition begins. It may take only 1 or 2 days for fluid to build up. The process that causes ARDS may continue for weeks. If scarring occurs, this will make it harder for the lungs to take in oxygen and get rid of carbon dioxide.
In the past, only about 4 out of 10 people who developed ARDS survived. But today, with good care in a hospital's intensive or critical care unit, many people (about 7 out of 10) with ARDS survive. Although many people who survive ARDS make a full recovery, some survivors have lasting damage to their lungs.
What causes ARDS?
The causes of acute respiratory distress syndrome (ARDS) are not well understood. It can occur in many situations and in persons with or without a lung disease.
There are two ways that lung injury leading to ARDS can occur: through a direct injury to the lungs, or indirectly when a person is very sick or has a serious bodily injury. However, most sick or badly injured persons do not develop ARDS.
Direct lung injury
A direct injury to the lungs may result from breathing in harmful substances or an infection in the lungs. Some direct lung injuries that can lead to ARDS include:
Indirect lung injury
Most cases of ARDS happen in people who are very ill or who have been in a major accident. This is sometimes called an indirect lung injury. Less is known about how indirect injuries lead to ARDS than about how direct injuries to the lungs cause ARDS. Indirect lung injury leading to ARDS sometimes occurs in cases of:
It is not clear why some very sick or seriously injured people develop ARDS, and others do not. Researchers are trying to find out why ARDS develops and how to prevent it.
Who is at risk for ARDS?
Acute respiratory distress syndrome (ARDS) usually affects people who are being treated for another serious illness or those who have had major injuries. In the United States, it affects about 150,000 people each year. ARDS can occur in people with or without a previous lung disease. People who have a serious accident with a large blood loss are more likely to develop ARDS. However, only a small portion of people who have problems that can lead to ARDS actually develop it.
In most cases, a person who develops ARDS is already in the hospital being treated for other medical problems. Some illnesses or injuries that can lead to ARDS include:
Signs and symptoms of ARDS
The major signs and symptoms of acute respiratory distress syndrome (ARDS) are:
Doctors and other health care providers watch for these signs and symptoms in patients who have conditions that might lead to ARDS. People who develop ARDS may be too sick to complain about having trouble breathing or other related symptoms. If a patient shows signs of developing ARDS, doctors will do tests to confirm that ARDS is the problem.
ARDS is often associated with the failure of other organs and body systems, including the liver, kidneys, and the immune system. Multiple organ failure often leads to death.
How is ARDS diagnosed?
Doctors diagnose acute respiratory distress syndrome (ARDS) when:
ARDS can be confused with other illnesses that have similar symptoms. The most important is congestive heart failure. In congestive heart failure, fluid backs up into the lungs because the heart is weak and cannot pump well. However, there is no injury to the lungs in congestive heart failure. Since a chest X-ray is abnormal for both ARDS and congestive heart failure, it is sometimes very difficult to tell them apart.
How is ARDS treated?
Patients with acute respiratory distress syndrome (ARDS) are usually treated in the intensive or critical care unit of a hospital. The main concern in treating ARDS is getting enough oxygen into the blood until the lungs heal enough to work on their own again. The following are important ways that ARDS patients are treated.
The main treatment is giving a higher concentration of oxygen than that found in normal air – that is, enough to raise blood levels of oxygen to safe levels. This can sometimes be done with a face mask. A face mask can deliver oxygen at a concentration of 40–60 percent. As the ARDS progresses over hours or days, the patient may need a higher level of oxygen than a face mask can give.
If the patient becomes tired from breathing so hard, it may become necessary to connect the patient to a breathing machine (ventilator). This can be done by placing a tube through the mouth or nose into the windpipe (trachea) in a procedure called endotracheal intubation (or just intubation) and connecting the tube to the ventilator. Sometimes the connecting tube is inserted through a surgical opening in the neck (this procedure is called a tracheotomy). The breathing machine can be set to help or completely control breathing. It will deliver the minimum amount of air every minute. If the extra oxygen and help with breathing are not enough, the breathing machine can be set to Positive End Expiratory Pressure (PEEP) to maintain the surface for gas exchange.
PEEP keeps some air in the lungs at the end of each breath. It helps keep the air sacs open instead of collapsing. The setting on the breathing machine can be adjusted to fit the needs of the patient. Other settings on the breathing machine control the number of breaths per minute (rate control) and the amount of air the ventilator uses to inflate the lungs in each breath (tidal volume).
Many different kinds of medicines are used to treat ARDS patients. Some kinds of medicines often used include:
With breathing tubes in place, ARDS patients cannot eat or drink as usual. They must be fed through a feeding tube placed through the nose and into the stomach. If this does not work, feeding is done through a vein. Sometimes a special bed or mattress, such as an airbed, is used to help prevent complications such as pneumonia or bedsores. If complications occur, the patient may require treatment for them.
Recovering from ARDS
Some people who survive acute respiratory distress syndrome (ARDS) heal quickly and recover completely in a relatively short time. Some are able to have the breathing tube and breathing machine removed in a week or so. Survivors often recover much of their lung function in the first 3–6 months after leaving the hospital, and they continue to recover for up to a year or more.
Others recover more slowly, however. Some ARDS survivors never recover completely, and they have continuing problems with their lungs. Every case is different. People who are younger and healthier when they develop ARDS are more likely to recover quickly than those who are older or who have more health problems.
ARDS patients who survive the first week but cannot breathe on their own may have to be on a breathing machine for several weeks or longer. These patients often develop complications, such as infections or air leaks (see the next section on Complications of ARDS). While some of these patients will die, others will get better and be able to breathe on their own again. Their recovery is usually slow, and they may have continuing problems.
After leaving the hospital, ARDS survivors need to visit a doctor during recovery to check how well their lungs are doing. Doctors use lung function tests to check the lungs. Spirometry is the most commonly used lung function test. It involves taking a deep breath and blowing hard into a plastic tube. The doctor will also do an oxygen saturation (oximetry) test or a blood test to check the amount of oxygen in the blood.
After going home from the hospital, the ARDS survivor may need only a little or a lot of help. While recovering from ARDS at home, a person may:
Complications of ARDS
Anyone who stays in the hospital for a long time can get complications. Common complications in ARDS patients are infections with hospital-acquired bacteria and leaks of air out of the lungs into other body spaces.
Each complication is treated as it arises. Careful hand washing by hospital staff and visitors helps reduce infections, and new breathing machine methods help reduce air leaks.
For family and friends
While your family member or friend is in the hospital being treated for ARDS, you may feel a lot of stress. One day the patient may seem to be recovering, and the next day things may take a turn for the worse. It can be a scary experience to see someone you care about on a breathing machine.
Several doctors work together to give care to your family member or friend. These doctors are often specialists who are treating different concerns of the patient. For example, an infectious disease specialist might be involved to help make sure that the initial infection or an infectious complication is properly treated. A lung specialist may be adjusting the settings on the breathing machine, and a kidney specialist may be required if kidney failure occurs. These doctors talk to each other regularly to make sure that care is given in a coordinated manner.
There are some things you can do to help, even though you may feel very helpless:
The family members and friends of people who have had ARDS often are deeply affected by the experience. The "roller-coaster ride" of emotions while the ARDS patient is in the hospital is exhausting and stressful. Caring for the ARDS survivor at home can also be stressful and tiring. Ask for help from others or your health care providers if you need it. Most hospitals have individuals such as social workers who can help family members cope with these issues.