Non-cardiogenic pulmonary edema

Alternative names
ARDS; Increased-permeability pulmonary edema; Stiff lung; Shock lung; Adult respiratory distress syndrome; Acute respiratory distress syndrome

Definition

Acute respiratory distress syndrome (ARDS) is a life-threatening condition in which inflammation of the lungs and accumulation of fluid in the air sacs (alveoli) leads to low blood oxygen levels.

While it shares some similarities with infant respiratory distress syndrome, its causes and treatments are different.

Causes, incidence, and risk factors

ARDS is a medical emergency. It can be caused by any major lung inflammation or injury. Some common causes include pneumonia, septic shock, trauma, aspiration of vomit, or chemical inhalation. ARDS develops as inflammation and injury to the lung and causes a buildup of fluid in the air sacs. This fluid inhibits the passage of oxygen from the air into the bloodstream.

The fluid buildup also makes the lungs heavy and stiff, and the lungs’ ability to expand is severely decreased. Blood concentration of oxygen can remain dangerously low in spite of supplemental oxygen delivered by a mechanical ventilator (breathing machine) through an endotracheal tube (breathing tube).

Typically patients require care in an intensive care unit (ICU). Symptoms usually develop within 24 to 48 hours of the original injury or illness. ARDS often occurs along with the failure of other organ systems, such as the liver or the kidneys. Cigarette smoking may be a risk factor.

Symptoms

     
  • Shortness of breath  
  • Labored, rapid breathing  
  • Low blood pressure or shock (low blood pressure accompanied by organ failure)

Often, persons affected by ARDS are so sick they are unable to complain of symptoms.

Signs and tests

Chest auscultation (examination with a stethoscope) reveals abnormal breath sounds, such as crackles that suggest fluid in the lungs. Often the blood pressure is low. Cyanosis (blue skin, lips, and nails caused by lack of oxygen to the tissues) is frequently seen.

Tests used in the diagnosis of ARDS include:

     
  • Chest X-ray  
  • Arterial blood gas  
  • CBC and blood chemistries  
  • Evaluation for possible infections  
  • Cultures and analysis of sputum specimens

Occasionally an echocardiogram (heart ultrasound) or Swan-Ganz catheterization may need to be done to exclude congestive heart failure, which can have a similar chest X-ray appearance to ARDS.

Treatment

The objective of treatment is to provide enough support for the failing respiratory system (and other systems) until these systems have time to heal. Treatment of the underlying condition that caused ARDS is essential.

The main supportive treatment of the failing respiratory system in ARDS is mechanical ventilation (a breathing machine) to deliver high doses of oxygen and a continuous level of pressure called PEEP (positive end-expiratory pressure) to the damaged lungs.

The high pressures and other breathing machine settings required to treat ARDS often require that the patient be deeply sedated with medications.

This treatment is continued until the patient is well enough to breathe on his or her own. Medications may be needed to treat infections, reduce inflammation, and eliminate fluid from the lungs.

Support Groups
Many family members of people with ARDS are under extreme stress. This can often be alleviated by joining support groups where members share common experiences and problems. See lung disease - support group.

Expectations (prognosis)

The death rate in ARDS is approximately 20-30%. Although survivors may recover normal lung function, many individuals suffer permanent lung damage, which can range from mild to severe.

Many people who survive ARDS suffer memory loss or other problems with thinking after they recover. This is related to brain damage caused by reduced access to oxygen while the lungs were malfunctioning.

Complications

     
  • Multiple organ system failure  
  • Pulmonary fibrosis  
  • Ventilator-associated pneumonia  
  • Damage to the lungs from the high ventilator settings required to treat the disease, such as pneumothorax

Calling your health care provider

Usually, ARDS occurs in the setting of another illness, for which the patient is already in the hospital. Occasionally, a healthy person may develop severe pneumonia that progresses to ARDS. If breathing difficulty develops, call the local emergency number (such as 911) or go to the emergency room.

Johns Hopkins patient information

Last revised: December 7, 2012
by Sharon M. Smith, M.D.

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