Acute lung injury

Definition

Acute respiratory distress syndrome (ARDS) is a life-threatening condition that causes lung swelling and fluid build up in the air sacs. ARDS is a medical emergency.

While ARDS shares some similarities with infant respiratory distress syndrome

Alternative Names

Causes

ARDS 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 and heavy alcohol use may be risk factors.

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.

Exams 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.

Outlook (Prognosis)

The death rate in ARDS is approximately 30%. Although survivors usually recover normal lung function, many individuals suffer permanent, usually mild, lung damage.

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.

Possible 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

When to Contact a Medical Professional

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.