Acute respiratory distress syndrome (ARDS)

What is ARDS?

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 tiny blood vessels (capillaries) in the lungs or the air sacs (alveoli (al-VEE-uhl-eye)) are damaged because of an infection, injury, blood loss, or inhalation injury. Fluid leaks from the blood vessels into air sacs of the lungs. While some air sacs fill with fluid, others collapse. When the air sacs collapse or fill up with fluid, the lungs can no longer fill properly with air and the lungs 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.

How the Lungs Work

To understand acute respiratory distress syndrome (ARDS), it is helpful to understand how your lungs work.

Normal Lung Function

A slice of normal lung looks like a pink sponge—filled with tiny bubbles or holes. Around each bubble is a fine network of tiny blood vessels. These bubbles, which are surrounded by blood vessels, give the lungs a large surface to exchange oxygen (into the blood where it is carried throughout the body) and carbon dioxide (out of the blood)

. This process is called gas exchange. Healthy lungs do this very well.

Here's how normal breathing works:

• You breathe in air through your nose and mouth. The air travels down through your windpipe (trachea) through large and small tubes in your lungs called bronchial (BRON-kee-ul) tubes. The larger tubes are bronchi (BRONK-eye), and the smaller tubes are bronchioles (BRON-kee-oles). Sometimes, we use the word "airways" to refer to the various tubes or passages that air uses to travel from the nose and mouth into the lungs. The airways in your lungs look something like an upsid e-down tree with many branches.

• At the ends of the small bronchial tubes, there are groups of tiny bubbles called air sacs or alveoli. The bubbles have very thin walls, and small blood vessels called capillaries are next to them. Oxygen passes from the air sacs into the blood in these small blood vessels. At the same time, carbon dioxide passes from the blood into the a ir sacs.

Effects of ARDS

In ARDS, the tiny blood vessels leak too much fluid into the lungs. This results from toxins (poisons) that the body produces in response to the underlying illness or injury. The lungs become like a wet sponge, heavy and stiffer than normal. They n

o longer provide the effective surface for gas exchange, and the level of oxygen in the blood falls. If ARDS is severe and goes on for some time, scar tissue called fibrosis may form in the lungs. The scarring also makes it harder for gas exchange to occur.

People who develop ARDS need extra oxygen and may need a breathing machine to breathe for them while their lungs try to heal. If they survive, ARDS patients

may have a full recovery. Recovery can take weeks or months. Some ARDS survivors take a year or longer to recover, and some never completely recover from having ARDS.

Other Names for ARDS

• Adult respiratory distress syndrome

• Stiff lung

• Shock lung

• Wet lung

There is a similar condition in infants called Infant Respi

ratory Distress Syndrome (also called IRDS, RDS, and hyaline membrane disease). It mainly affects premature infants whose lungs are not well developed when they are born.

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 AR

DS 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 h

armful substances or an infection in the lungs. Some direct lung injuries that can lead to ARDS include:

• Severe pneumonia (infection in the lungs)

• Breathing in vomited stomach contents

• Breathing in harmful fumes or smoke

• A severe blow to the chest or other accident that bruises the lungs

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:

• Severe and widespread bacterial infection in the body (se psis)

• Severe injury with shock

• Severe bleeding requiring blood transfusions

• Drug overdose

• Inflamed pancreas

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. It affects about 150,000 people each year in the United States. 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:

• Serious, widespread infection in the body (sepsis)

• Severe injury (trauma) and shock from a car crash, fire, or other cause

• Severe bleeding that requires blood transfusions

• Severe pneumonia (infection of the lungs)

• Breathing in vomited stomach contents

• Breathing in smoke or harmful gases and fumes

• Injury to the chest from trauma (such as a car accident) that causes bruising of the lungs
• 
  
• Nearly Drowning
  

• Some drug overdoses

What Are the Signs and Symptoms of ARDS?

The major signs and symptoms of acute respiratory distress syndrome (ARDS) are:

• Shortness of breathing
  
• Fast, labored breathing

• A bluish skin color (due to a low level of oxygen in the blood)

• A lower amount of oxygen in the blood

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:

• A person suffering from severe infection or injury develops breathing problems.

• A chest x ray shows fluid in the air sacs of both lungs.

• Blood tests show a low level of oxygen in the blood.

• Other conditions that could cause breathing problems have been ruled out.

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.

Extra Oxygen

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).

Medicines

Many different kinds of medicines are used to treat ARDS patients. Some kinds of medicines often used include:

• Antibiotics to fight infection

• Pain relievers

• Drugs to relieve anxiety and keep the patient calm and from "fighting" the breathing machine

• Drugs to raise blood pressure or stimulate the heart

• Muscle relaxers to prevent movement and reduce the body's demand for oxygen

Other Treatment

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.

Results

With treatment:

• Some patients recover quickly and can breathe on their own within a week or so. They have the best chance of a full recovery.

• Patients whose underlying illness is more severe may die within the first week of treatment.

• Those who survive the first week but cannot breathe on their own may face many weeks on the breathing machine. They may have complications and a slow recovery if they survive.
  

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 (speh-ROM-uh-tree) 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 (ok-SIM-eh-tree)) 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:

• Need to use oxygen at home or when going out of the home, at least for a while

• Need to have physical, occupational, or other therapy

• Have shortness of breath, cough, or phlegm (mucus)

• Have hoarseness from the breathing tube in the hospital

• Feel tired and not have much energy

• Have muscle weakness

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.

• Bacterial infections. The lungs or other parts of the body may become infected. These infections are usually treated with antibiotics after a test to see what kind of bacteria is causing the infection.

• Air leaks. Leaks of air through holes in the lungs are caused by pressure from the breathing machine that is needed to be sure the patient gets enough air, and from the very stiff lungs. Air from the injured lungs may enter the space between the lungs and the lining around the lungs (the pleura) and cause a pneumothorax (noo-mo-THOR-aks) (collapsed lung). Treatment involves using a chest tube and suction to remove the air and help the lungs reinflate. Air may also enter the space between the membranes that line the abdomen (pneumoperitoneum) or the soft tissue under the skin (subcutaneous emphysema). These are not usually treated.

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.