Atelectasis

Atelectasis is the partial or complete collapse of a part of the lung. Atelectasis is almost always a secondary phenomenon from conditions causing bronchial obstruction, external compression, surfactant deficiency, or scarring. Hypoxemia can occur as a result of blood flowing through unventilated lung segments. Patients are often asymptomatic. However, dyspnea, cough, chest pain, and fever can also occur. The diagnosis is made with imaging. Management includes treatment of the underlying etiology, lung expansion exercises, chest physiotherapy, bronchodilators, and bronchoscopy in select cases.

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Definition and Epidemiology

Definition

Atelectasis is the partial or complete collapse of lung tissue.

Epidemiology

  • The incidence and prevalence is not well known.
  • There is no race or sex predilection.

Risk factors

  • Premature birth
  • Obesity
  • Pregnancy
  • General anesthesia
  • Mechanical ventilation
  • Prolonged bed rest
  • Weakened respiratory muscles
  • Restricted chest movement

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Etiology and Pathophysiology

Classification

Atelectasis is classified on the basis of the underlying pathophysiology.

  • Obstructive atelectasis (most common)
  • Nonobstructive atelectasis:
    • Relaxation
    • Compressive
    • Adhesive
    • Cicatrization
    • Replacement
    • Rounded

Obstructive atelectasis

Etiology:

  • Foreign body
  • Tumor
  • Mucous plugging
  • Compression or distortion of bronchi

Pathophysiology:

  • Obstruction of a bronchus → reabsorption of gas from the alveoli → lung collapse
  • A large amount of lung volume loss → tracheal and mediastinal shift toward the atelectasis
  • Blood perfuses the unventilated lung → hypoxemia

Nonobstructive atelectasis

Relaxation atelectasis:

  • Etiology:
    • Pleural effusion
    • Pneumothorax
    • Large emphysematous bulla
  • Pathophysiology:
    •  Loss of contact between the parietal and visceral pleurae → loss of negative pressure in the pleural space
    • Lung is not held against the chest wall → recoils because of its elasticity → atelectasis

Compressive atelectasis: 

  • Etiology:
    • Chest wall, pleural, or intraparenchymal masses
    • Collections of pleural fluid
    • Elevated hemidiaphragm
  • Pathophysiology:
    • Space-occupying lesion of the thorax compresses the lung and forces air out of the alveoli.

Adhesive atelectasis:

  • Etiology:
    • Hyaline membrane disease
    • ARDS
    • Smoke inhalation
    • Uremia
    • Prolonged shallow breathing
  • Pathophysiology:
    • Surfactant → ↓ surface tension → prevents lung collapse
    • Surfactant dysfunction or deficiency → alveolar instability and collapse

Cicatricial atelectasis:

  • Etiology:
    • Chronic tuberculosis
    • Fungal infection
    • Radiation fibrosis
    • Idiopathic pulmonary fibrosis
    • Necrotizing pneumonia
  • Pathophysiology: severe parenchymal scarring → lung contraction

Replacement atelectasis:

  • Etiology: bronchioloalveolar cell carcinoma
  • Pathophysiology: Alveoli are filled with tumor.

Rounded atelectasis:

  • Etiology: 
    • Asbestosis
    • Pneumoconiosis
  • Pathophysiology: Lung is trapped by pleural disease.

Clinical Presentation

Symptoms

  • Generally asymptomatic
  • Important cause of fever in the postoperative period
  • Most symptoms and signs are determined by:
    • Acuity with which atelectasis occurs
    • Size of the area affected
    • Presence or absence of a complicating infection
  • Rapid, extensive atelectasis can lead to:
    • Sudden onset of dyspnea 
    • Cough
    • Chest pain on the affected side
  • Slowly developing atelectasis:
    • Asymptomatic 
    • Minor symptoms

Physical exam

  • Vitals:
    • Tachypnea
    • Tachycardia
    • Hypoxia
  • Lungs:
    • Diminished breath sounds on the affected side
    • Dullness to percussion might be elicited (if a large segment is involved).
    • Decreased chest excursion
    • Crackles or wheeze
    • Tracheal deviation → extensive lung volume loss
  • Skin: cyanosis

Complications

  • Pneumonia
  • Bronchiectasis
  • Respiratory failure

Diagnosis

Chest X-ray

Findings:

  • Lung opacification:
    • No air bronchograms (noted with obstruction)
    • Vessels obscured
  • Lung volume loss:
    • Interlobar fissure may be displaced.
    • If a large segment of the lung is involved: 
      • Mediastinum and tracheal shift toward the affected side.
      • Elevated ipsilateral diaphragm
      • Compensatory hyperinflation might be seen on the contralateral side.
  • Identification of foreign bodies

Computed tomography (CT)

Findings are similar to chest X-ray, but CT may be more sensitive in determining an etiology:

  • Bronchial narrowing due to obstruction may be seen.
  • Consolidation
  • Pleural effusion
  • Lung mass
  • Parenchymal scarring
Lobe atelectasis on CT

CT of the chest showing a right hilar mass (red arrow) compressing the bronchus and leading to right lower lobe atelectasis (blue arrow)

Image: “ Atelectasis” by Department of Pneumonology, Army General Hospital of Athens, 138 Mesogion & Katehaki Avenue, 115 25 Athens, Greece. License: CC BY 3.0

Arterial blood gas

  • ↓ Partial pressure of O₂ (PO₂)
  • Normal or ↓ partial pressure of CO₂ (PCO₂)

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Management

General measures

In addition to treating the underlying etiology of atelectasis, the following options can be used for prevention and treatment:

  • Chest physiotherapy:
    • Assists with clearing secretions
    • Helps maintain ventilation
  • Lung expansion techniques:
    • Incentive spirometry
    • Directed cough
    • Deep breathing
    • Early ambulation
  • Continuous positive airway pressure (CPAP):
    • Useful in patients who have hypoxemia or increased respiratory effort in the postoperative period
    • Should not be used in patients with abundant respiratory secretions
  • For patients who are mechanically ventilated, apply PEEP to prevent atelectasis or reopen collapsed alveoli.

Medical therapy

  • Bronchodilators
  • Dornase alfa: 
    • Recombinant human DNase
    • Useful for persistent mucous plugging
  • Analgesics:
    • For adequate pain control in the postoperative period 
    • Avoid oversedation.

Bronchoscopy

  • May be considered if other measures fail
  • Diagnostic and therapeutic for potential obstructive causes (e.g., tumor)
Bronchoscopy

Bronchoscopy is a procedure that allows visualization of the airways by way of a bronchoscope.

Image by Lecturio.

Differential Diagnosis

  • Aspiration pneumonitis: inhalation of either oropharyngeal or gastric contents into the lower airways: This inhalation stimulates an inflammatory response, resulting in cough, dyspnea, chest discomfort, and fever. The diagnosis is often clinical and supported with chest X-ray findings of ground-glass opacities in dependent regions. Management is supportive, and patients should be monitored for the development of pneumonia.
  • Pneumonia: infection of the lung parenchyma most often caused by bacteria or a virus: Patients present with fever, dyspnea, and a productive cough. Chest X-ray findings usually include lobar consolidation. Management usually involves empiric antibiotics, which can be tailored if the causative organism is identified. Antivirals are used in cases where a viral cause is suspected.
  • Pleural effusion: accumulation of fluid between the layers of the parietal and visceral pleura: Symptoms of pleural effusion include chest pain, cough, and dyspnea, and imaging can confirm its presence. Atelectasis with significant volume loss can appear similar to a massive pleural effusion; however, mediastinal and tracheal shift will be directed away from the effusion. Management depends on the underlying condition and whether the effusion is causing respiratory distress. 
  • Unilateral diaphragm paralysis: condition in which 1 diaphragm loses the ability to contract and allow inspiration: Patients may be asymptomatic or have dyspnea. A chest X-ray will show hemidiaphragmatic elevation. Pulmonary function tests will show a decline in forced vital capacity. Management may not be necessary for asymptomatic cases. Patients with more significant symptoms may need noninvasive ventilatory support, surgical plication, phrenic nerve pacing, and management of the underlying cause.
  • Pulmonary embolism: obstruction of the pulmonary arteries, most often due to thrombus migration from the deep venous system: Signs and symptoms include pleuritic chest pain, dyspnea, tachypnea, and tachycardia. Severe cases can result in hemodynamic instability or cardiopulmonary arrest. A chest CT with angiography is the primary method of diagnosis. Management includes oxygenation, anticoagulation, and thrombolytic therapy for unstable patients.

References

  1. Madappa, T., Sharma, S. (2020). Atelectasis. In Kamangar, N. (Ed.), Medscape. Retrieved April 2, 2021, from https://emedicine.medscape.com/article/296468-overview
  2. Stark, P. (2020). Atelectasis: Types and pathogenesis in adults. In Finlay, G. (Ed.), UpToDate. Retrieved April 2, 2021, from https://www.uptodate.com/contents/atelectasis-types-and-pathogenesis-in-adults
  3. Finder, J. D. (2019). Atelectasis in children. In Hoppin, A. G. (Ed.), UpToDate. Retrieved April 2, 2021, from https://www.uptodate.com/contents/atelectasis-in-children
  4. Coruh, B., Niven, A. S. (2019). Atelectasis. MSD Manual Professional Version. Retrieved April 2, 2021, from https://www.msdmanuals.com/professional/pulmonary-disorders/bronchiectasis-and-atelectasis/atelectasis
  5. Grott, K., Dunlap, J. D. (2021). Atelectasis. StatPearls. Retrieved April 2, 2021, from https://www.ncbi.nlm.nih.gov/books/NBK545316/

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