From the Guidelines
Trapped lung is a condition where the lung cannot fully expand to fill the pleural space due to a fibrous peel or membrane that forms over the visceral pleura, restricting lung expansion, and is typically diagnosed using pleural manometry and imaging studies. This condition occurs following pleural inflammation, which can result from conditions like pneumonia, hemothorax, empyema, or previous thoracic surgery, as noted in the British Thoracic Society guideline for pleural disease 1. The fibrous tissue prevents the lung from re-expanding even after pleural fluid is drained, creating a persistent pleural space.
Key Characteristics and Diagnosis
- Trapped lung is characterized by the inability of the lung to fully expand and fill the pleural space due to restrictive fibrosis.
- Diagnosis involves pleural manometry during thoracentesis, which shows increasingly negative pleural pressures as fluid is removed, and imaging studies that demonstrate the inability of the lung to expand, as discussed in the management of malignant pleural effusions 1.
- An initial pleural fluid pressure of < 10 cm H2O at thoracentesis makes trapped lung likely, and cut points of > 19 cm H2O with the removal of 500 ml of fluid and of > 20 cm H2O with the removal of 1 L of fluid are predictive of trapped lung in the absence of endobronchial obstruction 1.
Treatment Considerations
- Treatment depends on symptom severity, with mild cases potentially requiring no intervention, while more symptomatic cases might need surgical decortication to remove the restrictive fibrous peel, as individualized based on patient fitness and empyema stage 1.
- The decision for decortication should be tailored to the patient's condition, considering factors such as the extent of lung entrapment and the patient's overall health status.
- The goal of treatment is to allow the lung to re-expand and fill the pleural space, thereby improving symptoms and quality of life.
From the Research
Definition of Trapped Lung
Trapped lung, also known as lung entrapment, is defined as the inability of the lung to expand and fill the thoracic cavity due to a restricting "peel" caused by benign or malignant pleural disease 2, 3. This condition is characterized by the formation of a fibrous visceral pleural peel that prevents the lung from fully expanding 4, 5.
Causes of Trapped Lung
The causes of trapped lung include:
- Benign inflammatory or fibrotic cortex 2
- Malignant visceral pleural tumor 2
- Fibrinous or granulomatous pleuritis 4
- Inadequately treated parapneumonic effusion 4
- Cardiac surgery, chest trauma, and other inflammatory processes involving the pleura 4
- Pneumothorax 3
Characteristics of Trapped Lung
The characteristics of trapped lung include:
- Chronic, stable pleural effusion without evidence of active pleural disease 4, 5
- Inability of the lung to expand and fill the thoracic cavity 2, 3
- Restricting fibrous visceral pleural peel 4, 5
- Initial negative pleural liquid pressure, increased pleural space elastance, and demonstration of a pleural peel 4
Diagnosis and Treatment of Trapped Lung
The diagnosis of trapped lung requires documentation of chronicity and stability, and the absence of an active inflammatory or malignant pleural process, bronchial obstruction, or severe underlying lung disease 4. The treatment of trapped lung includes surgical decortication, which is the only available therapy 4, 3. Pleural manometry and radiological imaging are useful in the assessment of an unexpandable lung 5, 6.