Etiology of Atelectasis The most common factors that can cause atelectasis include the following: Intrinsic obstruction of airways (eg, by foreign body, tumor, mucous plug) Extrinsic compression of airways (eg, by tumor, lymphadenopathy) Suppression of respiration or cough (eg, by general anesthesia, oversedation, pain) Supine positioning, particularly in obese patients and those with cardiomegaly Compression or collapse of lung parenchyma (eg, by large pleural effusion or pneumothorax) Thoracic and abdominal surgeries are very common causes because they involve general anesthesia, opioid use (with possible secondary respiratory depression), and often painful respiration.