Pneumomediastinum is air in the space between the lungs, in the middle of the chest (the mediastinum).

Pneumomediastinum is uncommon. It occurs when air leaks from any part of the lung or airways into the mediastinum. Most often, one of the small air sacs (alveoli) ruptures and leaks air.

The condition can be caused by a traumatic injury or by disease. Increased pressure within the lungs or airways can rupture the air sacs or airways, allowing air to escape into surrounding structures. Such pressure can be caused by excessive coughing, sneezing, vomiting, or repeated bearing down to increase abdominal pressure (such as pushing during childbirth or a bowel movement).

It may also happen following:

• Accidental tearing of the trachea (windpipe)
• Rapid ascents in altitude, SCUBA diving
• Use of a breathing machine
• Using inhaled recreational drugs such as crack cocaine

Pneumomediastinum also can occur in association with pneumothorax or other diseases.

There may be no symptoms. The condition usually causes chest pain below the breastbone, which may spread to the neck or arms. The pain may be worse when you take a breath or swallow.

During a physical examination, the doctor may feel small bubbles of air under the skin of the chest, arms, or neck. A chest x-ray or CAT scan of the chest may be done to confirm the presence of air in the mediastinum and help diagnose a hole in the trachea or esophagus.

Often, no treatment is needed because the body will gradually absorb the air itself. Breathing high concentrations of oxygen may speed up this process.

The doctor may put in a chest tube if the condition is accompanied by a collapsed lung (pneumothorax). Surgery is needed to repair a hole in the trachea or esophagus.

The outlook depends on the disease or events that caused the pneumomediastinum.

The air may build up and enter the space around the lungs (pleural space), causing the lung to collapse.

More rarely, air may enter the area between the heart and the thin sac that surrounds the heart. This is called a pneumopericardium.

In other rare cases, so much air builds up in the middle of the chest that it pushes on veins in the area. This can interfere with the heart's ability to pump, and leads to low blood pressure.

All these complications require urgent attention.

Go to the emergency room or call the local emergency number (such as 911) if you have severe chest pain or difficulty breathing.

Park DR, Vallières E. Pneumomediastinum and mediastinitis. In: Mason RJ, Murray JF, Broaddus VC, Nadel JA, eds. Textbook of Respiratory Medicine. 4th ed. Philadelphia, Pa: Saunders Elsevier; 2005: chap 72.