DESCRIPTION

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

EPIDEMIOLOGY

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

ETIOLOGY

• Airway obstruction (resorption atelectasis)
  • Most common cause of atelectasis in children
  • Obstructed communication between alveoli and trachea
• Large airway obstruction
  • Intrinsic (intraluminal)
    • Foreign body aspiration
    • Mucous plug
    • Tumor
    • Plastic bronchitis
  • Extrinsic (compression)
    • Hilar adenopathy
    • Mediastinal mass
    • Cardiomegaly
    • Congenital lung malformations
• Small airway obstruction
  • Acute infection
    • Bronchiolitis
    • Pneumonia
    • Respiratory infections are the most common cause of acute atelectasis
  • Altered mucociliary clearance:
    • Inadequate cough
    • CNS depression with decreased cough and/or hypoventilation
    • Smoke inhalation (decreased surfactant levels with increased surface tension)
    • Pain (due to shallow breathing and inadequate cough)
• 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
• Increased surface tension in the small airways and alveoli (adhesive atelectasis)
  • Stems from surfactant deficiency or inactivation
  • 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)

RISK FACTORS

GENERAL PREVENTION

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

PATHOPHYSIOLOGY

• 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 with development of bronchiectasis if recurrent infections occur.