• State of collapsed and airless alveoli
  • May be subsegmental, segmental, or lobar or may involve the entire lung
  • A radiographic sign of an underlying disease and not a diagnosis unto itself


  • Depends on the underlying disease causing atelectasis
  • Resorption atelectasis is the most common form.

Risk Factors


Depends on the underlying disease causing atelectasis (i.e., cystic fibrosis, primary ciliary dyskinesia)

General Prevention

  • Maintaining adequate cough
  • Good airway clearance techniques in patients at risk for atelectasis


  • Reduced lung compliance
  • Loss of alveoli (if extensive) may lead to hypoxia.
  • Intrapulmonary shunting develops from hypoxia-induced pulmonary arterial vasoconstriction, which may lead to areas of ventilation–perfusion (V/Q) mismatch and further hypoxia.
  • If atelectasis is extensive and long-term, pulmonary hypertension may develop.
  • Atelectatic areas are prone to bacterial overgrowth and possible secondary infection.


  • Airway obstruction (resorption atelectasis)
    • Most common cause of atelectasis in children
    • Obstructed communication between alveoli and trachea
  • Large airway obstruction
    • Intrinsic
      • Foreign body aspiration
      • Mucous plug
      • Tumor
      • Plastic bronchitis
    • Extrinsic
      • Hilar adenopathy
      • Mediastinal mass
      • Congenital lung malformations
  • Small airway obstruction
    • Acute infection
      • Bronchiolitis
      • Pneumonia
      • Respiratory infections are the most common cause of acute atelectasis.
    • Altered mucociliary clearance:
      • CNS depression
      • Smoke inhalation
      • Pain
  • Mechanical compression of the pulmonary parenchyma or pleural space (compressive atelectasis)
    • Intrathoracic compression
      • Pneumothorax
      • Pleural effusion
      • Lobar emphysema
      • Intrathoracic tumors
      • Cardiomegaly
      • Diaphragmatic hernias
    • Abdominal distention
      • Large intra-abdominal tumors
      • Hepatosplenomegaly
      • Massive ascites
      • Morbid obesity
  • Decreased surface tension in the small airways and alveoli (adhesive atelectasis)
    • Stems from surfactant deficiency
    • Diffuse surfactant deficiency
      • Hyaline membrane disease
      • Acute respiratory distress syndrome
      • Smoke inhalation
    • Localized surfactant deficiency
      • Acute radiation pneumonitis
      • Pulmonary embolism
  • Neuromuscular weakness (hypoventilation)
    • Inherent weakness
      • Duchenne muscular dystrophy
      • Spinal muscular atrophy
      • Paralysis
    • Acquired weakness (e.g., postanesthesia hypoventilation)

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