What is atelectasis?

Atelectasis: Definition, Mechanisms, and Management

Atelectasis is the collapse of lung tissue resulting in non-aerated regions of the lung parenchyma, which can significantly impair gas exchange and oxygenation, potentially leading to increased morbidity and mortality if left untreated. 1

Definition and Mechanisms

Atelectasis is not a disease itself but rather a manifestation of underlying conditions. It occurs through three primary mechanisms:

1. Airway obstruction (obstructive atelectasis):

   • Occurs when an airway is blocked by mucus plugs, foreign bodies, or tumors
   • Results in resorption of air distal to the obstruction 2, 3

2. Compression (compressive atelectasis):

   • Caused by external pressure on lung tissue from:
     • Extrathoracic processes
     • Intrathoracic processes (pleural effusion, pneumothorax)
     • Chest wall abnormalities 2, 3

3. Surfactant dysfunction (adhesive atelectasis):

   • Increased surface tension in alveoli due to surfactant deficiency
   • Common during general anesthesia 4, 5

Other mechanisms include:

• Passive atelectasis: Due to diaphragmatic dysfunction or hypoventilation
• Cicatrization atelectasis: From pulmonary fibrosis
• Gravity-dependent atelectasis: Results from gravity-dependent alterations in alveolar volume 3

Clinical Presentation and Diagnosis

Radiographic Signs

• 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, compensatory hyperexpansion of surrounding lung 3

Types of Atelectasis

• Segmental, lobar, or whole lung
• Subsegmental
• Platelike, linear, or discoid
• Round
• Generalized or diffuse 3

Special Consideration: Rounded Atelectasis

• Also known as shrinking pleuritis, contracted pleurisy, pleuroma, Blesovsky's syndrome, or folded lung
• Presents radiographically as a mass that may be mistaken for a tumor
• Develops from infolding of thickened visceral pleura with collapse of intervening lung parenchyma
• Classic "comet sign" is pathognomonic and often more visible on HRCT than plain films 6

Management Approaches

Respiratory Care

• Position the patient with head of bed elevated 30 degrees to optimize lung expansion 1
• Deep breathing exercises every 1-2 hours while awake to increase inspiratory volume 1
• Incentive spirometry: 10 breaths every hour while awake 1
• Early mobilization: Progress gradually from sitting to walking as soon as possible 1

Advanced Interventions

• Non-invasive ventilation (NIV) or CPAP if conservative measures fail:
  • Use CPAP levels of 7.5-10 cmH₂O to reduce atelectasis and improve oxygenation 1
  • Recruitment maneuvers involving transient elevations in airway pressure (30-40 cmH₂O) can open collapsed lung and increase alveolar units participating in ventilation 6

Bronchoscopy

• Indicated for persistent mucous plugs that should be removed when atelectasis persists despite conservative measures 1, 2
• Flexible bronchoscopy can be used to restore airway patency by removing mucus plugs or blood clots causing atelectasis 6

Prevention Strategies

• During anesthesia:

  • Avoid high fractions of oxygen during induction and maintenance
  • Use moderate FiO₂ (0.3-0.4) during ventilation
  • Consider PEEP if high FiO₂ is necessary
  • Perform intermittent "vital capacity" maneuvers (inflation to airway pressure of 40 cmH₂O for 7-8 seconds) 4
  • Pre-oxygenation with 80% oxygen rather than 100% can reduce atelectasis formation 5

• Post-operative care:

  • Implement airway clearance techniques once or twice daily
  • Ensure adequate hydration to thin secretions
  • Consider humidification of inspired air 1

Complications and Outcomes

If left untreated, atelectasis can lead to:

• Decreased lung compliance
• Impaired oxygenation
• Increased pulmonary vascular resistance
• Development of lung injury
• Persistent atelectasis, pneumonia, and hypercapnic respiratory failure 1, 7

Special Considerations

• Obese patients typically develop larger atelectatic areas than lean individuals 4
• Patients with chronic obstructive lung disease may show less or even no atelectasis 4
• Rounded atelectasis is important for pathologists to recognize as it is frequently removed surgically as a suspected peripheral lung cancer 6

Early recognition and appropriate management of atelectasis are crucial to prevent complications and improve patient outcomes, particularly in the perioperative setting where atelectasis is common and can significantly impact recovery.