Conditions predisposing to secondary atelectasis are:
- Prolonged bed rest with few changes in position and shallow breathing
- Underlying lung diseases
- Secretions that plug the airway
- Foreign objects (common in children) in the airway
- Tumors that obstruct the airway
All of these causes result in obstruction of the airway which is the common denominator of atelectasis.
In an adult, small regions of atelectasis are usually not life-threatening, because unaffected parts of the lung compensate for the loss of function in the affected area. Large-scale atelectasis, especially in someone who has another lung disease or illness may be life-threatening. In a baby or small child, lung collapse due to a mucus obstruction or other causes can be life-threatening. Anyone undergoing chest or abdominal surgery using general anesthesia is at risk to develop atelectasis, since breathing is often shallow after surgery to avoid pain from the surgical incision. Any significant decrease in airflow to the alveoli contributes to pooling of secretions, which in turn can cause infection. Chest injuries causing shallow breathing, including fractured ribs, can cause atelectasis. Compressive atelectasis results when the air passages are closed from the outside. An enlarging lung tumor may press on the outside of the larger bronchial tubes, resulting in partial or complete closure. Adhesive or congenital atelectasis results from the lack of surfactant. Surfactant is a protein found naturally in the lungs that helps with gas exchange in the alveoli. It also helps keep the lungs elastic. This type of atelectasis can be caused by congenital disorders such as hyaline membrane disease. Without surfactant, the alveolar walls alone cannot keep the alveoli open.