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Atelectasis
Atelectasis is the incomplete expansion or complete collapse of air-bearing tissue, resulting from obstruction of air intake into the alveolar sacs. Segmental, lobar, or whole lung collapse is associated with the absorption of air contained in the alveoli, which are no longer ventilated.
Pathophysiology
The causes of atelectasis can be divided into 5 groups ( Table 437.1 ). Respiratory syncytial virus (see Chapter 287 ) and other viral infections, including influenza viruses in young children can cause multiple areas of atelectasis. Mucous plugs are a common predisposing factor to atelectasis. Massive collapse of one or both lungs is most often a postoperative complication but occasionally results from other causes, such as trauma, asthma, pneumonia, tension pneumothorax (see Chapter 439 ), aspiration of foreign material (see Chapters 414 and 425 ), paralysis, or after extubation. Massive atelectasis is usually produced by a combination of factors, including immobilization or decreased use of the diaphragm and the respiratory muscles, obstruction of the bronchial tree, and abolition of the cough reflex.
Table 437.1
Anatomic Causes of Atelectasis
| CAUSE | CLINICAL EXAMPLES |
|---|---|
| External compression on the pulmonary parenchyma | Pleural effusion, pneumothorax, intrathoracic tumors, diaphragmatic hernia |
| Endobronchial obstruction completely obstructing the ingress of air | Enlarged lymph node, tumor, cardiac enlargement, foreign body, mucoid plug, broncholithiasis |
| Intraluminal obstruction of a bronchus | Foreign body, asthma, granulomatous tissue, tumor, secretions including mucous plugs, bronchiectasis, pulmonary abscess, chronic bronchitis, acute laryngotracheobronchitis, plastic bronchitis |
| Intrabronchiolar obstruction | Bronchiolitis, interstitial pneumonitis, asthma |
| Respiratory compromise or paralysis | Neuromuscular abnormalities, osseous deformities, overly restrictive casts and surgical dressings, defective movement of the diaphragm, or restriction of respiratory effort |
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