Acute respiratory distress syndrome: What you need to know
It is a complication of an existing lung infection, injury, or serious illness. It can progress rapidly, and it can be fatal.
The condition is also known as respiratory distress syndrome (RDS), acute hypoxemic respiratory failure (AHRF), non-cardiogenic pulmonary edema, adult respiratory distress syndrome, wet lung, and Vietnam lung, among other names.
ARDS can be serious because it reduces the amount of oxygen provided to the body's organs. It can lead to infections and pneumonia, a collapsed lung, kidney failure, muscle weakness, and confusion.
Studies show that ARDS is less common in children, and less likely to be fatal.
- ARDS occurs when the body does not get enough oxygen from the lungs.
- Symptoms include severe shortness of breath and blue lips or nails.
- The condition can lead to a collapsed lung.
- It can be brought on by many causes, including lung infections, pulmonary blood clots, accidental inhalation of chemicals, vomit, or food, and giving birth.
- Most patients with ARDS are admitted to an intensive care unit (ICU).
- ARDS is fatal in 30 to 40 percent of cases. In surviving patients, lung function returns to normal after between 6 and 12 months.
Signs and symptoms
Respiratory distress syndrome causes an acute shortness of breath and can be fatal.
According to the National Heart, Lung and Blood Institute (NHLBI), most people with acute respiratory distress syndrome (ARDS) are in hospital when the symptoms appear.
However, it can develop outside of a hospital setting, for example, due to an infection such as pneumonia or after accidentally inhaling vomit.
The signs and symptoms of ARDS may include:
- severe shortness of breath
- hypotension, or low blood pressure
- bluish lips and nails, or mottled blue skin
The American Lung Association states that if the inflammation and fluid stay in the lungs for some time, the disease can reach a fibrotic stage. The lung can "pop" and deflate, or collapse. This is known as a pneumothorax.
The Berlin definition of ARDS, established in 2011, classifies the condition as mild, moderate, or severe. The chances of survival become lower as severity increases, and the length of time needed on a respirator will increase.
Causes and risk factors
ARDS causes fluid to build up in the air sacs, depriving organs of the required oxygen.
When we breathe, air enters through our nose and mouth and into our lungs. In the lungs, it enters the alveolar ducts and the alveoli, small grape-like bunches of tiny sacs.
Capillaries, or small blood vessels, run through the walls of the alveoli. Oxygen enters the air sacs and passes into the capillaries. From there it enters the bloodstream and travels to every part of the body, including the brain, heart, liver, kidneys.
In ARDS, an injury, infection, or some other condition causes fluid to accumulate in the air sacs. Swelling happens throughout the lungs, and fluid and proteins leak out from the capillaries into the alveoli, making it hard to breathe. A hemorrhage can also cause blood to leak into the lungs.
This prevents the lung from working properly. It cannot fill up with air in a normal way, and it cannot get rid of carbon dioxide effectively.
Breathing becomes difficult and exhausting.
As oxygen levels in the bloodstream start to drop, vital organs do not receive the oxygen they need. They risk becoming seriously damaged.
Different types of illnesses, conditions, and situations can trigger ARDS, including:
- A lung or chest infection, or pneumonia
- Severe flu, including avian, or bird, flu
- Other infections
- Complications of routine surgery
- A blood transfusion
- A clot in the lung
- Accidentally inhaling chemicals
- Accidentally inhaling vomit or food
- Acute pancreatitis - the inflammation can spread
- Giving birth
- Inhaling smoke, for example, from a house fire
- Near drowning
- Low blood pressure due to shock
- Overdose of some drugs, such as heroin, methadone, propoxyphene, or aspirin
ARDS can also stem from an inflammation of the pancreas, sepsis, burns, or a reaction to certain medications.
Pulmonary sepsis, or lung infection, is responsible for 46 percent of ARDS cases, while 33 percent of cases stem from an infection elsewhere in the body.
It is unclear why conditions that do not directly impact the lungs directly may cause ARDS. This could be because the body produces harmful substances that overwhelm the system.
Some people are more at risk of ARDS than others.
Risk factors for ARDS include:
- Excessive alcohol consumption
- Use of oxygen for another lung condition
- Recent high-risk surgery or chemotherapy
- Low blood protein
ARDS usually develops within 24 to 48 hours of an incident or the onset of a disease, but symptoms can take 4 to 5 days to appear.
Diagnosis and Treatment
The doctor may order the following diagnostic tests, according to the American Lung Association:
- A blood test, to determine blood oxygen levels and see whether there is an infection and, if so, what type
- A pulse oximetry test, in which a sensor is placed on a fingertip or earlobe, to detect how much oxygen is passing through into the blood
- An X-ray, to reveal which parts of the lungs have fluid accumulation, and possibly to show whether the heart is enlarged
- A CT scan, to provide detailed information about the structures in the heart and lungs
- An echocardiogram, using ultrasound to test the action of the heart
- Tests are carried out on the heart because signs and symptoms associated with ARDS can be similar to those found in several heart diseases
- Fluids from the lungs may be extracted and tested to identify an infection
There is no specific test to diagnose ARDS, so a full assessment is necessary, to rule out other conditions, including congestive heart failure and pneumonia, although ARDS can also result from pneumonia.
The patient may be fitted with an oxygen mask as part of their treatment.
Treatment aims to:
- manage the injury of condition that led to ARDS, and remove the cause of ARDS
- raise blood oxygen levels
Most patients with ARDS will be admitted to intensive care (ICU) or a critical care unit (CCU) and put on a ventilator.
Depending on their condition, the patient may be fitted with an oxygen mask, or have a tube inserted down the throat into the lungs to supply oxygen.
Nutrients and fluids will be supplied through a tube that goes into the patient's nose and down to the stomach.
Sedation may be necessary to improve comfort, and diuretics may be used to reduce the amount of fluid in the body.
Extracorporeal membrane oxygenation (ECMO) may be used to increase oxygen levels. Blood is pumped from the body, where oxygen is added to it, and carbon dioxide is taken away from it before the blood returns to the body. However, as there are risks of complications, ECMO is not always appropriate.
Antibiotics will be given if the cause of the ARDS is an infection.
Treatment will continue until the condition of the lungs improves.
Without treatment, 90 percent of patients with ARDS will not survive.
In the past, more than half of all patients with ARDS did not survive, even with treatment but recent advances in treatment and care have improved survival rates considerably.
An article published in the World Journal of Gastroenterology in 2010 says that between 30 percent to 40 percent of ARDS cases are fatal. Twenty years before the article, the mortality rate was between 50 percent and 70 percent.
If ARDS is fatal, this is often due to a complication of ARDS, such as kidney failure. Alternatively, it could be fatal because of an existing condition, of which ARDS is a complication.
Long-term effects include a significantly higher risk of complications, including lung damage, or damage to muscles and nerves, which can lead to pain and weakness. Some patients develop post-traumatic stress disorder (PTSD) and depression.
The patient may need ongoing therapy, especially if they have experienced organ or muscle damage.
In most patients who survive, lung function returns to normal after 6 to 12 months.