What are the causes of atelectasis?

Causes of Atelectasis

Atelectasis results from six primary mechanisms: resorption (airway obstruction), compression (external pressure on lung), adhesive (surfactant deficiency), cicatrization (fibrosis), passive (hypoventilation/pneumothorax), and gravity-dependent (positional volume changes). 1

Primary Mechanisms

1. Resorption Atelectasis (Most Common)

• Occurs when alveolar air is absorbed distal to an obstructing airway lesion 1
• Central airway obstruction causes include:
  • Malignant: Lung cancer (most common), metastatic disease to airways 2
  • Nonmalignant: Post-intubation/tracheostomy stenosis, idiopathic stenosis, inflammatory conditions (granulomatosis with polyangiitis, relapsing polychondritis, sarcoidosis), infections (TB, fungal), benign tumors 2
• Peripheral obstruction: Mucus plugging (especially in CF, COPD), foreign bodies

2. Perioperative Atelectasis (Extremely Common)

• Develops in 90% of anesthetized patients 3, 4
• Key causative factors:
  • High inspired oxygen concentration (FiO₂ >0.4) causing rapid nitrogen washout and absorption collapse 3, 4
  • Loss of muscle tone and decreased functional residual capacity from anesthetics 3
  • Compression of dependent lung zones 5
  • Surfactant dysfunction 5
• Appears within minutes of induction and can persist for days postoperatively 3

3. Compression Atelectasis

• External pressure prevents lung expansion 1
• Causes: Tension pneumothorax, pleural effusions, space-occupying masses, abdominal distention, diaphragmatic dysfunction 1

4. Adhesive Atelectasis

• Surfactant deficiency or dysfunction 1, 5
• Seen in: ARDS, respiratory distress syndrome, inhalational injury, radiation pneumonitis

5. Cicatrization Atelectasis

• Pulmonary fibrosis causes scarring and volume loss 1
• Results from chronic inflammatory conditions, radiation, chronic infections

6. Passive/Gravity-Dependent Atelectasis

• Simple pneumothorax, hypoventilation, prolonged recumbency 1
• Gravity-dependent alterations in alveolar volume 1

Clinical Context-Specific Causes

Postoperative Setting

Risk factors that enhance collapse 6:

• Low lung volume states
• High closing volume
• Rapid shallow breathing patterns
• Postoperative pain (especially thoracic/abdominal surgery) causing splinting 7
• Narcotic-induced respiratory depression
• Obesity (larger atelectatic areas than lean patients) 4
• Chronic lung disease, smoking

Cystic Fibrosis

• Thick secretions causing mucus plugging
• Allergic bronchopulmonary aspergillosis (ABPA) significantly increases atelectasis risk 8
• Moderate-to-severe baseline lung disease predisposes to atelectasis 8

Bronchoscopy-Related

• Develops early and frequently during peripheral bronchoscopy 9
• Particularly in dependent lung zones and high BMI patients 9
• Exacerbated by high FiO₂ and inadequate ventilation strategies

Important Clinical Pitfalls

⚠️ High oxygen concentration is a modifiable risk factor: Using FiO₂ >0.4 during anesthesia or mechanical ventilation accelerates atelectasis formation through rapid nitrogen absorption 3, 4. Maintain FiO₂ 0.3-0.4 when clinically appropriate.

⚠️ Atelectasis ≠ pneumonia: Do not diagnose atelectatic pneumonia based on radiographic findings alone—requires clinical signs/symptoms plus pathogenic bacteria identification 1.

⚠️ In rib fractures: Pain-induced splinting → atelectasis → poor secretion clearance → pneumonia (each rib fracture increases pneumonia risk by 27% in elderly) 7. Aggressive pain control is essential.

⚠️ ABPA screening in CF: Persistent atelectasis in CF patients should prompt evaluation for ABPA, as it significantly increases atelectasis frequency and represents a poor prognostic factor 8.