What is a non-expandable lung?

What is Non-Expandable Lung?

Non-expandable lung is a mechanical complication where the lung cannot expand to the chest wall after pleural fluid drainage, preventing normal apposition between the visceral and parietal pleura. 1, 2

Underlying Mechanisms

The inability of the lung to expand results from visceral pleural disease processes that create a restrictive barrier. 1, 2 This occurs through two distinct pathophysiologic entities:

Lung Entrapment

• Active pleural inflammation, infection, or malignancy causes visceral pleural involvement that prevents expansion 2, 3
• The underlying disease process (malignant pleural effusion, empyema, complicated parapneumonic effusion) is the primary clinical problem 2, 3
• This condition is potentially reversible if appropriate therapeutic measures are taken early 4

Trapped Lung

• A mature fibrous membrane (pleural peel) overlies the visceral pleura from remote pleural inflammation 2, 3
• This represents defective healing of the pleural space and is typically irreversible 2
• Presents as a chronic, stable pleural effusion without evidence of active pleural disease 2
• The mechanical effect of the pleural peel itself constitutes the primary clinical problem 3

Clinical Presentation

Non-expandable lung manifests in two characteristic ways during pleural drainage:

• Post-thoracentesis hydropneumothorax develops when fluid is removed but the lung cannot expand to fill the space 2, 3, 4
• Chest pain during drainage that prevents complete fluid removal 2, 3

Prevalence and Importance

At least 30% of patients with malignant pleural effusion have non-expandable lung, making this a common complication that fundamentally alters management strategy. 5, 6 Recognition is critical because:

• Pleurodesis requires visceral and parietal pleural apposition to succeed, making it ineffective in non-expandable lung 5
• Misrecognition leads to unnecessary procedures with significant cost and morbidity 1
• Some patients will not experience symptomatic relief with pleural fluid removal 1

Diagnostic Approach

Clinical Recognition

• Suspect when effusion cannot be completely drained due to anterior chest pain 2, 3
• Consider when post-procedure pneumothorax develops 2

Diagnostic Tools

• Pleural manometry demonstrates abnormal lung expansion during drainage and can identify non-expandable lung during initial pleural drainage 2, 3
• Radiological imaging shows abnormal visceral pleural thickening 2
• Air-contrast chest CT provides definitive visualization 4
• Ultrasound M-mode measurement of lung movement shows promise for pre-thoracentesis diagnosis (AUC 0.81) 7

Management Implications

The British Thoracic Society recommends that indwelling pleural catheters (IPCs) are effective at controlling symptoms in non-expandable lung and should be considered as the preferred management technique. 5

Treatment Algorithm Based on Degree of Non-Expansion

For radiologically significant (>25%) non-expandable lung:

• Use IPC rather than talc pleurodesis 5
• IPCs work for both expandable and non-expandable lung, making them suitable when lung expansion status is uncertain 5

For <25% non-expandable lung:

• Talc slurry pleurodesis may improve quality of life, chest pain, breathlessness and pleurodesis rates 5

For trapped lung (chronic, stable effusion):

• Most patients are asymptomatic or have mild exertional dyspnea and do not require treatment 4
• Decortication surgery may be considered for incapacitating dyspnea in selected patients fit for thoracic surgery 5, 4

Key Clinical Pitfall

Early evaluation of pleural effusions is critical to address underlying causes of pleural inflammation and prevent progression from lung entrapment (potentially reversible) to trapped lung (irreversible). 1 Delayed intervention allows active pleural disease to mature into an irreversible fibrous peel.