What is atelectasis?

Atelectasis: Definition, Mechanisms, and Management

Atelectasis is a condition characterized by the collapse of lung tissue with loss of volume in a previously inflated portion of the lung, resulting in non-aerated regions of the lung parenchyma. 1 This pathological condition is usually associated with several pulmonary and chest disorders and represents a manifestation of underlying disease rather than a disease itself.

Mechanisms of Atelectasis

Atelectasis can occur through three primary mechanisms:

1. Obstructive (resorption) atelectasis:

   • Caused by airway obstruction from mucus plugs, foreign bodies, or tumors
   • Air distal to the obstruction is absorbed into the bloodstream, leading to collapse
   • Common in postoperative patients and those with impaired secretion clearance

2. Compressive atelectasis:

   • Results from external compression of lung tissue
   • Caused by pneumothorax, pleural effusion, tumors, or abdominal distention
   • Pressure from outside the lung prevents normal expansion

3. Adhesive atelectasis:

   • Results from surfactant deficiency or dysfunction
   • Increased surface tension in alveoli prevents normal expansion
   • Common in respiratory distress syndrome and after general anesthesia

Additional mechanisms include:

• Passive atelectasis: Due to diaphragmatic dysfunction or hypoventilation
• Cicatrization atelectasis: Results from pulmonary fibrosis
• Gravity-dependent atelectasis: Occurs in dependent lung regions due to gravitational effects 2

Clinical Significance

Atelectasis has significant clinical implications:

• Decreased lung compliance
• Impaired oxygenation and gas exchange
• Increased pulmonary vascular resistance
• Risk of developing lung injury
• Persistence into postoperative period affecting recovery 3

In anesthesia, atelectasis is present in approximately 90% of patients under general anesthesia with mechanical ventilation, regardless of whether they are breathing spontaneously or paralyzed, and whether intravenous or inhalational anesthetics are used 4.

Diagnosis

Diagnosis of atelectasis typically involves:

• Chest radiography: Both anterior-posterior and lateral projections are essential

  • Direct signs: Crowded pulmonary vessels, crowded air bronchograms, displacement of interlobar fissures
  • Indirect signs: Pulmonary opacification, elevation of diaphragm, shift of trachea/heart/mediastinum, displacement of hilus 2

• CT scanning: More sensitive than conventional chest X-ray

  • Can detect atelectasis not visible on standard radiographs
  • High-resolution CT (HRCT) is particularly useful for detecting subtle changes 5

• Clinical findings: Decreased breath sounds, dullness to percussion, tracheal deviation

Management

Management of atelectasis depends on its cause, duration, and severity:

1. Prevention strategies:

   • During anesthesia:

     • Use moderate fraction of inspired oxygen (FIO₂ 0.3-0.4) rather than high concentrations
     • Apply positive end-expiratory pressure (PEEP)
     • Perform recruitment maneuvers ("vital capacity" maneuvers) to re-expand collapsed lung tissue 4
     • Position patient appropriately (often head-up or semi-recumbent position) 5

   • During mechanical ventilation:

     • Implement lung-protective ventilation strategies
     • Use appropriate PEEP levels after recruitment maneuvers 5
     • Avoid zero end-expiratory pressure (ZEEP) which promotes alveolar collapse 5

2. Treatment approaches:

   • Chest physiotherapy: Postural drainage, percussion, vibration
   • Bronchodilator therapy: To improve airway patency
   • Adequate hydration: To thin secretions
   • Incentive spirometry: To encourage deep breathing
   • Early mobilization: To prevent dependent atelectasis
   • Bronchoscopy: For removal of persistent mucous plugs 1

3. Specific interventions for rounded atelectasis:

   • Rounded atelectasis (also known as folded lung, Blesovsky's syndrome) presents radiographically as a mass
   • May be mistaken for a tumor
   • Classic "comet sign" is pathognomonic and often more readily seen on HRCT
   • May require surgical intervention if diagnostic uncertainty persists 5

Special Considerations

• Obesity: Larger atelectatic areas are present in obese patients compared to lean individuals 4
• COPD patients: May show less or even no atelectasis during anesthesia 4
• Postoperative period: Atelectasis can persist and impact recovery; consider CPAP in high-risk patients 5
• Neonates and infants: Flexible bronchoscopy may be indicated for persistent atelectasis not responding to conventional therapy 5

Pitfalls and Caveats

• Atelectasis can be mistaken for pneumonia on imaging
• The diagnosis of atelectatic pneumonia should be based on clinical signs and identification of pathogens, not just radiographic findings 2
• High oxygen concentrations during emergence from anesthesia significantly increase atelectasis formation; if clinically appropriate, use FIO₂ <0.4 5
• Routine suctioning of the tracheal tube just before extubation should be avoided as it may promote lung volume loss 5

By understanding the mechanisms of atelectasis and implementing appropriate preventive and treatment strategies, clinicians can minimize the adverse effects of this common perioperative complication.