Atelectasis is an area of the lung that is not completely inflated.

Atelectasis may be caused by many things. These include infections, other lung problems, neuromuscular diseases, or blockages by something such as mucus. Atelectasis may happen after anesthesia for surgery. Deep breathing exercises after surgery may be done to try to prevent or treat it. Mild atelectasis is not usually a problem. But when atelectasis is severe, it can cause pain and/or shortness of breath. And it can lower oxygen levels.

Atelectasis may be treated by treating the cause, restoring airflow to the lung, or removing any blockage.