Acute Respiratory Distress Syndrome

Also known as Acute Lung Injury, ARDS, Noncardiac Pulmonary Edema
Acute respiratory distress syndrome (ARDS) is a serious lung condition that causes low blood oxygen. People who develop ARDS are usually ill due to another disease or a major injury. In ARDS, fluid builds up inside the tiny air sacs of the lungs, and surfactant breaks down. Surfactant is a foamy substance that keeps the lungs fully expanded so that a person can breathe. These changes prevent the lungs from filling properly with air and moving enough oxygen into the bloodstream and throughout the body. The lung tissue may scar and become stiff.

ARDS may develop over a few days, or it can get worse very quickly. The first symptom of ARDS is usually shortness of breath. Other signs and symptoms of ARDS are low blood oxygen, rapid breathing, and clicking, bubbling, or rattling sounds in the lungs when breathing.

ARDS can develop at any age. To diagnose ARDS, your doctor or your child’s doctor will do a physical exam, review the patient’s medical history, measure blood oxygen levels, and order a chest X-ray. Supplying oxygen is the main treatment for ARDS. Other treatments help make you more comfortable or aim to eliminate the cause of ARDS. Treatments for ARDS may help prevent serious or life-threatening complications, including organ damage or organ failure.

Explore this Health Topic to learn more about ARDS, our role in research and clinical trials to improve health, and where to find more information.

Causes - Acute Respiratory Distress Syndrome

Damage to the lung’s air sacs—called alveoli—causes ARDS. Fluid from tiny blood vessels leaks through the damaged walls of the air sacs and collects, limiting the lungs’ normal exchange of oxygen and carbon dioxide. The damage also causes inflammation that leads to the breakdown of surfactant—a liquid that helps keep your air sacs open.

The air sacs may become damaged as a result of an illness, such as a lung infection, or breathing in smoke. Other illnesses or injuries may trigger inflammation that damages the air sacs. To understand ARDS, you may also want to read about how the lungs work.

Illustration of ARDS
Acute Respiratory Distress Syndrome. The image on the left shows the location of the lungs, trachea, and bronchi within the body. The middle image shows the normal gas exchange of oxygen and carbon dioxide through the air sacs. The image on the right shows the fluid buildup in the air sacs of someone who has ARDS. The fluid buildup prevents gas exchange. Medical Illustration Copyright © 2019 Nucleus Medical Media, All rights reserved.


Risk Factors - Acute Respiratory Distress Syndrome

You may have an increased risk of ARDS because of infection, environmental exposures, lifestyle habits, genetics, other medical conditions or procedures, race, or sex. Risk factors can vary depending on your age, overall health, where you live, and the healthcare setting in which you receive care.

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Infections are the most common risk factors for ARDS. These may include:

  • Flu or other viruses, such as respiratory syncytial virus and SARS-CoV-2, the virus responsible for COVID-19. Watch this video to learn more about how COVID-19 affects the lungs. Additionally, we offer information and resources on how we are working hard to support necessary COVID-19 research. 
  • Pneumonia
  • Sepsis, a condition in which bacteria infect the bloodstream
  • Uterine infection in the mother, affecting a newborn’s lungs

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Being exposed to air pollution for weeks or months can make you more vulnerable to ARDS.

Lifestyle habits
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Habits that harm the health of your lungs increase your risk of ARDS. These include:

  • Heavy alcohol use
  • Overdose of illegal drugs
  • Smoking

Family history and genetics
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The genes you inherit may put you at an increased risk for ARDS. These genes play a role in how the lungs respond to damage.

Other medical conditions or procedures
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Other medical conditions, injuries, or medical procedures can raise your risk for ARDS. These may include:

  • Blood transfusions
  • Fat embolism, in which a clot of fat blocks an arteries. A physical injury, such as a broken bone, can lead to a fat embolism.
  • Hemorrhagic shock
  • Inhaling vomit, smoke, chemical fumes, or water during a near drowning
  • Injury, such as from a blow or burns
  • Lung injury from being on a ventilator
  • Lung or heart surgery, or being placed on a heart-lung bypass machine
  • Newborn lung conditions, which can raise the risk of your baby having neonatal ARDS. These include pneumonia and a condition where the unborn baby passes stool while still in the womb, and the stool is then inhaled into his or her lungs. Your baby is also at higher risk if he or she did not get enough oxygen during delivery.
  • Pancreatitis, a condition in which the pancreas becomes infected. The pancreas is a gland that releases enzyme and hormone.
  • pulmonary vasculitis
  • Reaction to medicine, such as those used to treat Cancers or arrhythmia

Race or ethnicity
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The risk of developing ARDS is higher among nonwhite groups.

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Among children, boys are at a higher risk of ARDS than girls are.

Learn more about how ARDS in newborns is different from respiratory distress syndrome, a similar breathing condition that also affects newborns.

Screening and Prevention - Acute Respiratory Distress Syndrome

Your doctor may screen for ARDS if you have risk factors for ARDS. Getting vaccines to prevent the flu and other infections, avoiding tobacco smoke, limiting the amount of alcohol you drink, and limiting your exposure to pollution can reduce your risk of getting ARDS.

If you have a condition that puts you at risk of ARDS, getting early treatment may help prevent the syndrome. Your doctor and healthcare team may try to prevent ARDS by treating infection or shock, managing your fluid levels carefully, managing the settings of your ventilator, and limiting blood transfusions.

Look for
- Acute Respiratory Distress Syndrome

  • Diagnosis will discuss tests and procedures that your doctor may use to diagnose ARDS or rule out other conditions.
  • Living With will explain what your doctor may recommend to prevent your ARDS from recurring, getting worse, or causing complications.
  • Research for Your Health will discuss how we are using current research and advancing research to prevent and treat ARDS.

Signs, Symptoms, and Complications - Acute Respiratory Distress Syndrome

Difficulty breathing is usually the first symptoms of ARDS. Other signs and symptoms of ARDS may vary depending on the underlying cause and how severely you are affected. ARDS may take several days to develop, or it can rapidly get worse. Complications may include Blood clots, infections, additional lung problems, or organ failure.

Signs and symptoms
- Acute Respiratory Distress Syndrome

Signs and symptoms that you are developing or are at risk for ARDS may include:

  • Shortness of breath
  • Fast breathing, or taking lots of rapid, shallow breaths
  • Fast heart rate
  • Coughing that produces phlegm
  • Blue fingernails or blue tone to the skin or lips
  • Fatigue
  • Fever
  • Crackling sound in the lungs
  • Chest pain, especially when trying to breathe deeply
  • Low blood pressure
  • Confusion

If you have trouble breathing, call your doctor right away. If you have severe shortness of breath, call 9-1-1.

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If you have ARDS, you can develop other medical problems while in the hospital. Some can be life-threatening. The most common problems are:

  • Atelectasis, when small air pockets in the lung collapse
  • Complications of treatment in a hospital. Such complications include blood clots that can form from lying down for long periods, weakness in muscles used for breathing or moving around, infections, stress ulcers, and depression or other mood disorders. Problems with thinking, memory, and judgment also can result from the long-term use of sedative medicines.
  • Failure of multiple organs. The body’s organs may not work as well or may stop working altogether if they do not get enough oxygen. This lack of oxygen may cause several organs to stop working at the same time, setting up a potentially life-threatening situation.
  • Pulmonary hypertension, or an increase in blood pressure in the major artery leading from the heart to the lungs. This condition may occur when the blood vessel narrows as a result of damage from inflammation or mechanical ventilation. ARDS may also cause tiny clots to form in blood vessels in the lungs.

Learn more about how some people are more at risk of complications from ARDS.

Look for
- Acute Respiratory Distress Syndrome

  • Diagnosis will explain tests and procedures used to detect signs of ARDS and help rule out other conditions that may mimic ARDS.
  • Treatment will discuss treatment-related complications or side effects.

Diagnosis - Acute Respiratory Distress Syndrome

Your doctor will diagnose ARDS based on your medical history, a physical exam, and test results. ARDS can be difficult to diagnose and is often mistaken for another condition, so it is important to know your symptoms.

Medical history
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To help diagnose ARDS, your doctor may ask you about any medical conditions or recent events that could be considered risk factors. For example, travelling could be a risk factor because of potential exposure to infections that are more common in certain geographic areas. Your doctor may also ask about your symptoms and whether you have a heart problem, such as heart failure, or another condition that can cause signs and symptoms similar to those for ARDS.

Physical exam
- Acute Respiratory Distress Syndrome

Your doctor will examine you for signs of ARDS. This exam may include:

  • Listening to your lungs through a stethoscope for abnormal breathing sounds, such as crackling
  • Listening to your heart for a fast heart rate
  • Checking for signs that you are having difficulty breathing, such as using muscles in your chest to help you breath
  • Examining your skin or lips for a bluish tone, which can signal a low blood oxygen level
  • Examining your body for swelling or other signs of extra fluid, which may be linked to heart or kidney problems
  • Measuring your blood pressure and oxygen levels

Diagnostic tests and procedures
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To diagnose ARDS, your doctor may have you undergo some of the following tests and procedures. Different tests may be appropriate for different ages.

  • Blood tests to measure the oxygen level in your blood using a sample of blood taken from an artery. A low blood oxygen level might be a sign of ARDS. In order to confirm the cause of your symptoms, your doctor may also check your blood for signs of infection or a heart problem, or to see how well other organs are working.
  • Chest X-ray to create detailed images of the inside of your chest. This test is generally the standard for showing excess fluid in your lungs.
  • CT (computed tomography) scan of the chest or abdomen to create detailed images of your lungs or check for abdominal infections.
  • Other tests of blood oxygen levels, such as pulse oximetry, that do not require collecting a blood sample. For these tests, a sensor is attached to the skin or placed on a hand or foot.

Tests for other medical conditions
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Other tests can help find the cause of your ARDS or determine if there is another type of problem. These include:

  • A sputum culture to help find the cause of an infection. The culture is used to study the phlegm you have coughed up from your lungs.
  • Bronchoscopy to diagnose a lung problem when there is no clear cause of your ARDS. As part of this test, your doctor may rinse an area of your lung to get cells and examine them under a microscope or with other tests.
  • Echocardiogram or a lung ultrasound. These tests can help your doctor rule out heart failure, congenital heart defects, or other breathing problems.
  • Lung biopsy, when other tests do not confirm a diagnosis
  • Urine test to detect bacterial infections or rule out kidney problems

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Treatment - Acute Respiratory Distress Syndrome

The goal of treatment for ARDS is to improve oxygen levels and treat the underlying cause. Other treatments aim to prevent complications and make you comfortable.

Breathing support
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Oxygen therapy to raise the oxygen levels in your blood is the main treatment for ARDS. Oxygen can be given through tubes resting in your nose, a face mask, or a tube placed in your windpipe.

Depending on the severity of your ARDS, your doctor may suggest a device or machine to support your breathing. These include:

  • Non-invasive ventilation, such as bilevel positive airway pressure (BiPAP) or continuous positive airway pressure (CPAP) devices. These electronic breathing devices help keep your airways open by blowing air through a face mask.
  • A ventilator. Your doctor will adjust the ventilator settings to help prevent any more damage to your lung tissue. If the ventilator helps restore your blood oxygen levels and it is easier to breathe on your own, your doctor may turn off the ventilator to see if you are ready for it to be removed completely. Some people transition from a ventilator to portable oxygen therapy. Risks from being on a ventilator include pneumonia and pneumothorax, which can cause your lungs to collapse.

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Your doctor may recommend medicine to relieve symptoms, treat the underlying cause, or prevent complications from being in a hospital. These may include:

  • Acid-reducing medicines to prevent stress ulcers, which can cause bleeding in the intestines.
  • Antibiotics to treat or prevent infections. If you are on a ventilator, your healthcare team may do tests, such as lung fluid lab tests or CT scans, to look for signs of new infection.
  • Blood thinners to stop blood clots from forming or growing larger. Heparin is a common blood thinner for adults.
  • Muscle relaxants to help prevent coughing or gagging while on a ventilator or to reduce the amount of oxygen your body needs.
  • Pain medicines, which your doctor may prescribe, depending on your needs.
  • Sedatives to help relieve anxiety, make it easier to breathe on a ventilator, or lower your body’s oxygen needs. Sometimes your doctor may pair a sedative with another medicine to make it easier to deliver the oxygen. Complications vary depending on the sedative used, the dose, and how long it is used. They can include depression, post-traumatic stress disorder (PTSD), problems with thinking or memory, or a delay in removing the ventilator.

Other treatments
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Your doctor may recommend other treatments, including:

  • Blood transfusion to treat low hemoglobin levels. Hemoglobin carries oxygen in the blood, so a transfusion can improve the delivery of oxygen to the body’s organs.
  • Extracorporeal membrane oxygenation (ECMO) or a similar device, especially for severe ARDS. ECMO helps when ventilation alone cannot deliver enough oxygen or while a patient waits for a lung transplant. ECMO works like an artificial lung, removing carbon dioxide and pumping oxygen-rich blood back into the body.
  • Fluid management. Your healthcare team will monitor the fluid balance in your body. Low blood pressure can occur when the fluid in your blood vessels is low. This may prevent oxygen from getting to your organs. To help restore the balance, your doctor may give you fluid through an intravenous (IV) line. When you have too much fluid in the lungs, your doctor may give you medicines that help your body get rid of it.
  • Nutritional support. You may need a feeding tube to make sure you get enough of the right nutrients while you are on a ventilator.
  • Physical therapy to maintain muscle strength and prevent sores from forming. Movement may help shorten the time you are on a ventilator and improve recovery after you leave the hospital.
  • Positioning your body. For severe ARDS, your doctor may recommend that you spend most of the time lying facedown, which helps oxygen get to more of your lungs.

Look for
- Acute Respiratory Distress Syndrome

  • Research for Your Health will discuss how we are using current research and advancing research to treat people who have ARDS.
  • Participate in NHLBI Clinical Trials will explain our open and enrolling clinical studies that are investigating treatments for ARDS.
  • Living With will discuss what your doctor may recommend, including lifelong lifestyle changes and medical care to prevent your condition from recurring, getting worse, or causing complications.

Living With - Acute Respiratory Distress Syndrome

If you have been diagnosed with ARDS, it is important that you continue your treatment plan. Get regular follow-up care to control your condition and prevent complications.

More people are surviving ARDS now than in the past. One likely reason is that treatment and care for the condition have improved. Your age and race may be linked to your recovery. Some people who survive recover completely. Others may have lasting damage to their lungs and other health problems.

Receive routine follow-up care
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Research has led to better care for people who have ARDS, but recovery after leaving the hospital can take many weeks or months, particularly for older adults. Also, the longer you were on a ventilator, the longer it may take for you to recover your strength and return to your familiar routines. Your healthcare team can support your recovery or suggest additional resources.

  • Keep regular appointments so your doctor can monitor your recovery.
  • Take all medicines regularly as prescribed. Do not change the amount of your medicine or oxygen or skip a dose of medicine unless your doctor tells you to.
  • Work with therapists or other healthcare providers to gain strength and speed your recovery.
  • Between visits, call your doctor if you have any new symptoms or your symptoms worsen.

Return to Treatment to review possible treatment options for ARDS.

Monitor your condition
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To monitor your condition, your doctor may recommend the following tests or procedures:

  • Pulmonary function tests periodically after you are released from the hospital, to see how well your lungs are working. Your doctor may ask you questions about your symptoms, measure your blood oxygen level, or do a spirometry test.
  • Muscle strength and physical capacity tests. Weak muscles are a common result of staying in bed for a long-term treatment, especially if the doctor gave you a sedative. One common test of endurance is the six-minute walk test, which measures how far you can walk in that time. Such tests will help your doctor know how you are recovering and if you need additional care, such as pulmonary rehabilitation or physical therapy.
  • Mental health screening. Your doctor may also ask questions to assess the state of your emotional health.

Adopt healthy lifestyle changes
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Your doctor may recommend adopting healthy lifestyle changes, including quitting smoking. Smoking can worsen lung problems. Talk to your doctor about programs and products that can help you quit. Also, try to avoid secondhand smoke and other lung irritants, such as harmful fumes. Visit Smoking and Your Heart and the National Heart, Lung, and Blood Institute’s Your Guide to a Healthy Heart. For free help quitting smoking, you may call the National Cancer Institute’s Smoking Quitline at 1-877-44U-QUIT (1-877-448-7848).

Take care of your mental health
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Talk about how you feel with your healthcare team. Anxiety, depression, and even PTSD are relatively common among people who have had ARDS. Your healthcare team may recommend that you take steps that include:

  • Asking your family and friends for help with everyday activities. Support from family and friends also can help relieve stress and anxiety. Let your loved ones know how you feel and what they can do to help you.
  • Joining a patient support group. You can see how other patients manage similar symptoms and their condition. Talk with your doctor about local support groups or check with an area medical center.
  • Talking with a professional counselor. If you are very depressed, your doctor may recommend medicines or other treatments that can improve your quality of life.

Research for Your Health

The NHLBI is part of the U.S. Department of Health and Human Services’ National Institutes of Health (NIH)—the Nation’s biomedical research agency that makes important scientific discoveries to improve health and save lives. We are committed to advancing science and translating discoveries into clinical practice to promote the prevention and treatment of heart, lung, blood, and sleep disorders, including ARDS. Learn about current and future NHLBI efforts to improve health through research and scientific discovery.

Improving health with current research
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Learn about the following ways the NHLBI continues to translate current research into improved health for people who have ARDS. Research on this topic is part of the NHLBI’s broader commitment to advancing lung diseases scientific discovery.

  • Advancing ARDS Diagnosis. The NHLBI supported the work of the international ARDS Definition Task Force, which in 2012 updated the criteria for determining whether a patient has ARDS. The task force also defined mild, moderate, and severe types of ARDS, helping doctors determine treatment. The definition was further tested and refined using data from more than 4,000 patients and is widely used today.
  • Improving Critical Care for ARDS. The NHLBI’s ARDS Clinical Trial Network (ARDSNet) study results have improved ARDS survival and informed best practices for treating patients who have ARDS. For example, ARDSNet researchers showed that a more conservative, restricted approach to fluid management for intensive care patients who have acute lung injury led to improved lung function and less time on mechanical ventilation. The ARDSNet study results also optimized methods for ARDS clinical trials and led to the collection of biospecimens to support future ARDS research.
  • Providing Access to NHLBI Biologic Specimens and Data. The Biologic Specimen and Data Repository Information Coordinating Center (BioLINCC) centralizes and integrates biospecimens and clinical data that were once stored in separate repositories, such as ARDSNet. Researchers can find and request available resources on BioLINCC’s secure website, which maximizes the value of these resources and advances heart, lung, blood, and sleep research.
  • Addressing barriers to early diagnosis and treatment. The Vascular Interventions/Innovations and Therapeutic Advances (VITA) Program is a translational program that supports and accelerates early stage development of promising diagnostics and treatments. The VITA Program seeks to address unmet clinical needs for vascular diseases, particularly in underserved medical communities.

Learn about some of the pioneering research contributions we have made over the years that have improved clinical care.

Advancing research for improved health
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In support of our mission, we are committed to advancing ARDS research in part through the following ways.

Learn about exciting research areas the NHLBI is exploring about ARDS.

Participate in NHLBI Clinical Trials

We lead or sponsor many studies relevant to ARDS. See if you or someone you know is eligible to participate in our clinical trials.

Are you recovering after treatment for ARDS?

This study aims to test a rehabilitation intervention with patients who are recovering from ARDS and have symptoms of depression. The intervention includes periodic visits from physical and occupational therapists, an exercise regimen, and regular check-ins by phone. To participate in this study, you must be at least 18 years old and recovering at home after hospital treatment for ARDS or another type of acute respiratory failure. This study is located in Baltimore, Maryland.

Do you know someone who is in the hospital and has risk factors for ARDS?

This study aims to investigate possible genetic risk factors for ARDS, particularly genes that control inflammation. To participate in this study, you must be between 18 and 80 years old, be admitted to a hospital intensive care unit, and have risk factors for ARDS. This study is located in Boston, Massachusetts.
View more information about Molecular Epidemiology of ARDS.

Is your child on a ventilator for acute respiratory distress syndrome (ARDS)?

This study is testing whether lying facedown and using a type of ventilation called high-frequency oscillatory ventilation improves breathing in children who have ARDS. To participate in this study, your child must be younger than age 18, diagnosed with ARDS, and on a ventilator. This study is located in 23 states in the United States, as well as in Australia, Canada, the Netherlands, and Thailand.

More Information

After reading our ARDS Health Topic, you may be interested in additional information found in the following resources.

Non-NHLBI resources
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