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Acute respiratory distress syndrome

ARDS, Acute lung injury, Adult respiratory distress syndrome, Respiratory distress syndrome, adult, ALI, Increased-permeability pulmonary edema, Non-cardiogenic pulmonary edema, Shock lung, Stiff lung

Overview

Acute respiratory distress syndrome is a life-threatening lung condition that prevents enough oxygen from getting to the lungs and into the blood.  People who develop ARDS often are very ill with another disease or have major injuries. The condition leads to a buildup of fluid in the air sacs which prevents enough oxygen from passing into the bloodstream.

ARDS is not a particular disease, rather it is a clinical phenotype which may be triggered by various pathologies such as trauma, pneumonia and sepsis. The hallmark of ARDS is diffuse injury to cells which form the alveolar barrier, surfactant dysfunction, activation of the innate immune response, and abnormal coagulation. In effect, ARDS results in impaired gas exchange within the lungs at the level of the microscopic alveoli.

The syndrome is associated with a high mortality rate between 20 and 50%. The mortality rate with ARDS varies widely based on severity, the patient's age, and the presence of other underlying medical conditions.

Although the terminology of "adult respiratory distress syndrome" has at times been used to differentiate ARDS from "infant respiratory distress syndrome" in neonates, international consensus is that "acute respiratory distress syndrome" is the best moniker because ARDS can affect those of all ages.

Symptoms - Acute respiratory distress syndrome

The signs and symptoms of ARDS often begin within two hours of an inciting event, but can occur after 1–3 days. Often, people with ARDS are so sick they cannot complain of symptoms. Signs and symptoms may include shortness of breath, fast breathing, and a low oxygen level in the blood. A chest x-ray frequently demonstrates generalized infiltrates or opacities in both lungs, which represent fluid accumulation in the lungs.

Other signs and symptoms that occur in people with ARDS may be associated with the underlying disease process. For example, those with ARDS from sepsis may have low blood pressure and fever, while a person with pneumonia may have a cough.

  • Low blood pressure and organ failure
  • Rapid breathing
  • Shortness of breath 

Causes - Acute respiratory distress syndrome

The predisposing factors of ARDS are numerous and assorted. Common causes of ARDS include sepsis, pneumonia, trauma, multiple blood transfusions, babesiosis, lung contusion, aspiration of stomach contents, and drug abuse or overdose. Other causes of ARDS include burns, pancreatitis, near drowning, or the inhalation of chemical irritants such as smoke, phosgene, or chlorine gas. Some cases of ARDS are linked to large volumes of fluid used during post-trauma resuscitation.

ARDS can be caused by any major injury to the lung. Some common causes include:

  • Breathing vomit into the lungs (aspiration)
  • Inhaling chemicals

Lung transplant:

  • Pneumonia
  • Septic shock (infection throughout the body)
  • Trauma

ARDS leads to a buildup of fluid in the air sacs. This fluid prevents enough oxygen from passing into the bloodstream.

The fluid buildup also makes the lungs heavy and stiff, and decreases the lungs' ability to expand. The level of oxygen in the blood can stay dangerously low, even if the person receives oxygen from a breathing machine (mechanical ventilator) through a breathing tube (endotracheal tube).

ARDS often occurs along with the failure of other organ systems, such as the liver or kidneys. Cigarette smoking and heavy alcohol use may be risk factors.

Also, ARDS occurs during another illness, for which the patient is already in the hospital. Occasionally, a healthy person may develop severe pneumonia that gets worse and becomes ARDS. 

Prevention - Acute respiratory distress syndrome

Direct Lung Injury:

Conditions that can directly injure the lungs include:

  • Pneumonia. This is an infection in the lungs.
  • Breathing in harmful fumes or smoke.
  • Inhaling vomited stomach contents from the mouth.
  • Using a ventilator. This is a machine that supports breathing; however, the pressure from a ventilator sometimes can injure the lungs.
  • Nearly drowning

Indirect Lung Injury:

Conditions that can indirectly injure the lungs include:

  • Sepsis. This is a condition in which bacteria infect the bloodstream.
  • Severe bleeding caused by an injury to the body or having many blood transfusions.
  • An injury to the chest or head, such as a severe blow.
  • Pancreatitis (PAN-kre-ah-TI-tis). This is a condition in which the pancreas becomes irritated or infected. The pancreas is a gland that releases enzymes and hormones.
  • Fat embolism (EM-bo-lizm). This is a condition in which fat blocks an artery. A physical injury, like a broken bone, can lead to a fat embolism.
  • Drug reaction.

Diagnosis - Acute respiratory distress syndrome

Doctors diagnose ARDS when:

  • 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.

Prognosis - Acute respiratory distress syndrome

About a third of people with ARDS die from the disease. Those who live usually get back most of their normal lung function, but many people have permanent (usually mild) lung damage.

Many people who survive ARDS have memory loss or other quality-of-life problems after they recover. This is due to brain damage that occurred when the lungs weren't working properly and the brain wasn't getting enough oxygen.

Treatment - Acute respiratory distress syndrome

Typically people with ARDS need to be in an intensive care unit (ICU).

The goal of treatment is to provide breathing support and treat the cause of ARDS. This may involve medications to treat infections, reduce inflammation, and remove fluid from the lungs.

A breathing machine is used to deliver high doses of oxygen and continued pressure called PEEP (positive end-expiratory pressure) to the damaged lungs. Patients often need to be deeply sedated with medications when using this equipment. Some research suggests that giving medications to temporarily paralyze a person with ARDS will increase the chance of recovery.

Treatment continues until you are well enough to breathe on your own.

Resources - Acute respiratory distress syndrome

  • NIH
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