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What Is Atelectasis?

Atelectasis (at-uh-LEK-tuh-sis) is a condition in which one or more areas of your lungs collapse or don't inflate properly. If only a small area or a few small areas of the lungs are affected, you may have no signs or symptoms.

If a large area or several large areas of the lungs are affected, they may not be able to deliver enough oxygen to your blood. This can cause symptoms and complications.


To understand atelectasis, it helps to understand how the lungs work. Your lungs are organs in your chest that allow your body to take in oxygen from the air. They also help remove carbon dioxide (a waste gas that can be toxic) from your body.

When you breathe, air passes through your nose and mouth into your windpipe. The air then travels to your lungs' air sacs. These sacs are called alveoli (al-VEE-uhl-eye).

Small blood vessels called capillaries run through the walls of the air sacs. When air reaches the air sacs, the oxygen in the air passes through the air sac walls into the blood in the capillaries. At the same time, carbon dioxide moves from the capillaries into the air sacs. This process is called gas exchange.

The air sacs must remain open and filled with air for this process to work right. Surfactant (sur-FAK-tant), a liquid that coats the inside of the lungs, helps the air sacs stay open. Deep breathing and coughing also help keep the air sacs open. (Coughing helps clear mucus and other substances from your airways.)

In atelectasis, part of the lung collapses or doesn't inflate. The air sacs in that part of the lung are no longer filled with air. As a result, they can't take part in gas exchange.

If only a small area or a few small areas of the lungs are affected, you may have no signs or symptoms. This is because the rest of the lung can bring in enough oxygen to make up for the collapsed part of the lung.

If atelectasis affects a large area or several large areas of the lungs, your body's organs and tissues may not get enough oxygen-rich blood.

Conditions and factors that keep the lungs from properly expanding and filling with air can cause atelectasis. For example, atelectasis is very common after surgery.

The medicine used during surgery to temporarily put you to sleep can decrease or stop your normal effort to breathe and urge to cough. Sometimes, especially after chest or abdominal surgery, pain may keep you from wanting to take deep breaths. As a result, part of your lungs may collapse or not inflate right.


The outlook for atelectasis depends on its cause. In adults, atelectasis often is short term. The collapsed air sacs slowly refill with air once the cause of the atelectasis is resolved.

If atelectasis persists, it may prevent the lung from properly clearing mucus. This can lead to infections (such as pneumonia).

Atelectasis usually isn't life threatening. However, if it affects a large area of the lungs—especially in a baby, small child, or someone who has another lung disease or illness—it can be fatal if not treated quickly.

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Last Updated: January 13, 2012