What are the causes of atelectasis?

Causes of Atelectasis

Atelectasis primarily occurs through three main mechanisms: airway obstruction, compression of lung parenchyma, and increased surface tension in alveoli and bronchioles. 1

Primary Mechanisms of Atelectasis

1. Obstructive Atelectasis

• Occurs due to resorption of alveolar air distal to airway obstruction 2
• Common causes include:
  • Neoplasms obstructing bronchi (most common cause in adults) 3
  • Mucous plugs requiring bronchoscopic removal 1
  • Foreign body aspiration (can cause persistent cough if unwitnessed) 4
  • Broncholithiasis (calcified lymph nodes eroding into airways) 4

2. Compressive Atelectasis

• Results from external pressure on lung tissue 2
• Caused by:
  • Pleural effusion 5
  • Space-occupying intrathoracic lesions 2
  • Pneumothorax (both simple and tension) 2
  • Abdominal distention pushing on diaphragm 2
  • External masses compressing airways 5

3. Adhesive Atelectasis

• Stems from surfactant deficiency or dysfunction 2
• Common in:
  • Neonatal respiratory distress syndrome 5
  • During general anesthesia (affects up to 90% of patients) 6, 7

Special Types of Atelectasis

Rounded Atelectasis

• Also known as folded lung, shrinking pleuritis, or Blesovsky's syndrome 4
• Develops from infolding of thickened visceral pleura with collapse of intervening lung 4
• Most commonly associated with asbestos exposure 4
• Presents radiographically as a mass that may be mistaken for tumor 4
• Classic "comet sign" is pathognomonic, more visible on HRCT than plain films 4

Platelike (Discoid) Atelectasis

• Common during anesthesia and post-operative periods 5
• Can be prevented by:
  • Head-up or ramped positioning during anesthesia induction 5
  • Avoiding high oxygen concentrations 7
  • Performing recruitment maneuvers 5

Cicatrization Atelectasis

• Results from pulmonary fibrosis and scarring 2
• Common after chronic infections 3

Gravity-Dependent Atelectasis

• Results from gravity-dependent alterations in alveolar volume 2
• Common in bedridden patients and during anesthesia 6

Anesthesia-Related Atelectasis

• Appears in approximately 90% of anesthetized patients 7
• Major causes include:
  • High oxygen concentration during induction and maintenance 7
  • Loss of muscle tone causing decreased functional residual capacity 7
  • Compression of lung tissue 7
  • Loss of surfactant function 7
• Preventive measures:
  • Using moderate FiO2 (0.3-0.4) instead of pure oxygen 6
  • Performing recruitment maneuvers (vital capacity maneuvers) 6
  • Applying PEEP (positive end-expiratory pressure) 6

Clinical Considerations

• Atelectasis can persist for several days postoperatively and may become a focus of infection 7
• Obese patients develop larger atelectatic areas than lean individuals 6
• Patients with COPD may paradoxically show less or even no atelectasis 6
• Differentiation from lobar consolidation can be challenging clinically 1

Radiographic Signs

• Direct signs: crowded pulmonary vessels, crowded air bronchograms, and displacement of interlobar fissures 2
• Indirect signs: pulmonary opacification, elevation of diaphragm, shift of trachea/heart/mediastinum, displacement of hilum, compensatory hyperexpansion of surrounding lung 2
• Rounded atelectasis shows characteristic "comet sign" connecting to area of thickened pleura 4