When you breathe, air travels through your nose, down the trachea, and into smaller airways called bronchi. Bronchi branch into even smaller passages called bronchioles, and finally into tiny, thin, fragile grape-like sacs called alveoli. Sometimes the bronchi and bronchioles can become obstructed and block airflow. This can cause all or part of the lungs to collapse, a condition called atelectasis. There are several different causes of blockage: a foreign body in the air passages, pressure from chest tumors, trapped sputum or mucus, or other lung disorders. Atelectasis can develop as a consequence of surgery where intubation was needed. The first step in treating atelectasis is to remove the cause of the obstruction. Supplemental oxygen, chest physiotherapy and antibiotics are also used as standard therapy. In most cases the lung tissue will return to normal.