Trapped Lung

Trapped lung is the failure of the lung to expand to the chest wall because of a restrictive visceral pleural peel (fibrous membrane), leading to a pleural effusion "ex vacuo" or pneumothorax.

• Distinguish: trapped lung (chronic, from inflammation in the past; visceral peel; chronic effusion with negative pleural pressure) vs. unexpandable lung (broader term including endobronchial obstruction, malignant infiltration or fibrosis) vs. lung entrapment (active pleural disease like cancer or infection with a visceral pleural peel).
• Causes: past empyema or parapneumonic effusion, haemothorax, tuberculous pleurisy, uraemic pleuritis, rheumatoid pleuritis, cardiac surgery, malignancy (mesothelioma, metastatic), post radiation.
• Pathophysiology: inability of the lung to expand causes negative pleural pressure, transudative or exudative fluid formation, rapid fluid reaccumulation after thoracentesis; pleural pressure falls abruptly with drainage.
• Complications: dyspnoea, recurrent effusions, re-expansion pulmonary oedema if large volume rapidly drained, chest pain during thoracentesis, hydropneumothorax (pneumothorax ex vacuo after drainage).

• Chronic exertional dyspnoea with recurrent or persistent effusion that reaccumulates after thoracentesis.
• Chest pain, cough, and cough with large volume drainage because of falling pleural pressure.
• Dullness, reduced breath sounds, no mediastinal shift despite large effusion (mediastinum midline or toward the effusion).
• History of previous pleural disease.

• Pleural fluid analysis: transudate or non inflammatory lymphocytic exudate, glucose and pH normal, low cell count (typically stable, paucicellular).
• Pleural manometry during thoracentesis: pleural pressure drops rapidly with initial drainage (more than 14.5 cmH2O fall per 240 mL removed ratio, elastance over 14.5 cmH2O/L, or end expiratory pressure falling below −20 cmH2O) indicates unexpandable lung; stop drainage when chest discomfort, cough or pressure below −20 cmH2O.
• Imaging: post-thoracentesis chest radiograph (pneumothorax ex vacuo, incomplete re-expansion with visceral pleural line), ultrasound (lack of lung movement, thickened pleura), CT with contrast (visceral pleural thickening).
• Rule out malignancy (cytology, biopsy), infection, mediastinal obstruction.
• Pulmonary function and V/Q scan to assess underlying lung function and expected benefit of decortication.

• Limit therapeutic thoracentesis to symptomatic relief (drain until cough or chest tightness, ideally with manometry to keep pleural pressure above −20 cmH2O), avoid draining more than 1 to 1.5 L.
• Asymptomatic: observation.
• Symptomatic recurrent effusion with unexpandable lung: indwelling pleural catheter (drain 3 to 4 times weekly for symptom relief; avoid pleurodesis which fails because the pleural surfaces cannot appose); this is the preferred option for malignant and benign trapped lung.
• Decortication (VATS or open) for good performance patients with benign trapped lung and underlying healthy lung, to re-expand the lung; consider early (within months) in post empyema; risks include air leak, bleeding, infection.
• Pleuroperitoneal shunt for refractory benign cases.
• Treat underlying cause (anti-tuberculous therapy, dialysis for uraemic pleuritis, immunosuppression for rheumatoid).
• Pneumothorax ex vacuo (after drainage): observation, usually stable; avoid suction or aggressive drainage.
• Palliation in malignant cases: opioids, indwelling pleural catheter, cancer therapy.
• Follow up with repeat imaging and symptom review.