There are two different causes of atelectasis—obstructive and non-obstructive. Obstructive atelectasis occurs when a blockage develops in the airway. As a result, air does not reach the alveoli, and they collapse. Some of the most common causes of this type include foreign objects, tumors, and mucus plugs. Non-obstructive atelectasis refers to causes unrelated to obstructions of the airway; for instance: surgery, lung scarring, or pleural effusion.

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