Shock lung

Alternative names

Non-cardiogenic pulmonary edema; Increased-permeability pulmonary edema; Stiff lung; ARDS; 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.