What are the causes of atelectasis?

Causes of Atelectasis

Atelectasis is primarily caused by airway obstruction, compression of lung parenchyma, and increased surface tension in alveoli and bronchioli, leading to collapsed and non-aerated regions of otherwise normal lung tissue. 1

Mechanism-Based Classification of Atelectasis

1. Resorption Atelectasis

• Occurs due to resorption of alveolar air distal to obstructing lesions of the airways 2
• Common causes include:
  • Mucus plugging in airways 1
  • Foreign body aspiration 2
  • Endobronchial tumors causing airway obstruction 2
  • Compression of airways by external masses 3

2. Compression Atelectasis

• Results from external pressure on lung tissue causing collapse 2
• Common causes include:
  • Pleural effusion causing compressive atelectasis 3
  • Tension pneumothorax 2
  • Space-occupying intrathoracic lesions 2
  • Abdominal distention pushing up on diaphragm 2
  • Rounded atelectasis (folded lung) following pleuritis of any cause, particularly asbestos exposure 3

3. Adhesive Atelectasis

• Stems from surfactant deficiency or dysfunction 2
• Common causes include:
  • Acute respiratory distress syndrome (ARDS) 2
  • Neonatal respiratory distress syndrome 3
  • Surfactant inactivation during general anesthesia 4

4. Passive Atelectasis

• Caused by factors that limit normal lung expansion 2
• Common causes include:
  • Simple pneumothorax 2
  • Diaphragmatic dysfunction 2
  • Hypoventilation states 2

5. Cicatrization Atelectasis

• Results from pulmonary fibrosis and scarring 2
• Common causes include:
  • Chronic inflammatory lung diseases 2
  • Post-inflammatory fibrosis 3
  • Asbestosis and other occupational lung diseases 3

6. Gravity-Dependent Atelectasis

• Results from gravity-dependent alterations in alveolar volume 2
• Common causes include:
  • General anesthesia (occurs in about 90% of anesthetized patients) 4, 5
  • Supine positioning during surgery 3
  • Prolonged bed rest 2

Specific Clinical Scenarios Associated with Atelectasis

Perioperative Atelectasis

• Occurs in approximately 90% of all anesthetized patients 4, 5
• Major causes include:
  • High oxygen concentration during induction and maintenance of anesthesia 4, 6
  • Loss of muscle tone and decreased functional residual capacity from anesthetics 4
  • Supine positioning causing cephalad displacement of abdominal contents 3
  • Compression of dependent lung regions 5
  • Impaired mucociliary clearance during anesthesia 1

Chronic Lung Disease of Infancy

• In bronchopulmonary dysplasia, regions of atelectasis alternate with emphysema 3
• Causes include:
  • Airway damage with mucous gland hypertrophy and excessive mucus 3
  • Alveolar Type I cell injury 3
  • Inflammation and scarring of lung tissue 3
  • Central airway obstruction leading to recurrent atelectasis 3

Pulmonary Disease in Adults

• COPD and other pulmonary conditions increase risk of atelectasis 3
• Contributes to post-operative pulmonary complications, particularly after abdominal or thoracic surgery 3
• Risk factors include:
  • Smoking history 3
  • Pre-existing lung disease 3
  • Factors causing post-operative hypoventilation 3

Malignancy-Related Atelectasis

• Malignant pleural effusions can cause compressive atelectasis 3
• Direct tumor invasion or obstruction can lead to resorption atelectasis 3
• Post-obstructive pneumonia with subsequent parapneumonic effusion may develop 3

Clinical Implications and Management Considerations

• Atelectasis can persist for several days postoperatively and may serve as a focus for infection 4
• Diagnosis typically requires chest radiographs in both anterior-posterior and lateral projections 1
• Treatment depends on the underlying cause and may include:
  • Chest physiotherapy and postural drainage 1
  • Bronchodilator and anti-inflammatory therapy 1
  • Bronchoscopy for removal of persistent mucous plugs 1
  • For perioperative atelectasis: recruitment maneuvers, moderate FiO2, and PEEP 6

Understanding the various mechanisms of atelectasis is essential for proper diagnosis and management, as treatment should target the underlying cause rather than just the collapsed lung tissue itself 1, 2.