A trapped lung, also known as an incarcerated lung, is a medical condition where a portion of the lung cannot fully expand and fill the chest cavity. This restriction is mechanical and develops over time, unlike an acute lung collapse. The condition is characterized by a mature, inelastic layer of tissue that forms around the lung, physically preventing it from inflating during inhalation. Treatment focuses on relieving this physical constraint and restoring lung function.
The Underlying Mechanism
The chest cavity is lined by two thin membranes, collectively called the pleura, which normally slide smoothly against each other during breathing. The parietal pleura lines the chest wall, and the visceral pleura covers the lung surface. A trapped lung results from a prolonged inflammatory process in the pleural space, often due to a previous infection or injury, which triggers the formation of scar tissue.
Chronic inflammation leads to the organization of fibrin deposits into a thick, restrictive layer known as a fibrous peel or rind. This non-elastic rind encases the visceral pleura, physically tethering the lung and preventing it from re-expanding to its normal volume. Even if fluid accumulates (pleural effusion), the lung remains compressed because the restrictive peel cannot stretch.
The persistence of this pleural effusion is a direct mechanical consequence of the lung’s inability to expand. When the lung is restricted, the pressure within the pleural space becomes abnormally low, drawing fluid from surrounding tissues into the cavity. This phenomenon is termed “effusion ex-vacuo,” meaning the fluid is present because of the vacuum created by the unexpanded lung, rather than an active disease process producing the fluid. The defining feature of this mechanism is the high pleural elastance, which measures how much the pressure changes as fluid is removed during a medical procedure.
Causes and Risk Factors
A trapped lung is considered a secondary complication, meaning it arises as a result of a prior condition that caused significant inflammation within the pleural space. Common triggers involve infections that lead to a complicated accumulation of fluid, such as bacterial empyema or severe parapneumonic effusions. In these cases, the body’s healing response creates the restrictive scar tissue.
A collection of blood in the chest cavity, known as a hemothorax, can also lead to the formation of this thick, fibrotic peel if the blood is not completely drained. Previous thoracic surgeries, including coronary artery bypass grafting, or certain inflammatory conditions like rheumatoid pleuritis, are recognized risk factors. The key factor is the prolonged presence of inflammatory material or fluid that allows the fibrin to mature into a rigid, non-flexible peel around the lung.
Symptoms and Diagnostic Methods
The symptoms a person experiences are primarily related to the restricted lung volume. Many patients with a small, stable pleural effusion may feel no symptoms at all, but others develop chronic, progressive shortness of breath, medically termed dyspnea. This breathing difficulty often worsens over time and may be accompanied by a persistent dry cough or a noticeable reduction in their capacity for physical activity.
Diagnosis relies on imaging studies that show the thickened pleura and the persistent collapse of the lung. A Chest X-ray or Computed Tomography (CT) scan will visually confirm the presence of the dense, restrictive rind surrounding the lung tissue. The definitive method to distinguish a trapped lung from other causes of non-expanding lung is the use of pleural manometry during a fluid drainage procedure called thoracentesis.
Pleural manometry involves monitoring the pressure within the chest cavity as the pleural fluid is withdrawn. In a trapped lung, this measurement shows a characteristic and significant drop in pressure as fluid is removed, indicating that the lung is mechanically unable to expand to take up the space. A high pleural elastance value, typically exceeding 14.5 centimeters of water per liter of fluid removed, is a strong indicator that the restrictive fibrous peel is present.
Treatment Approaches and Recovery
The management strategy for a trapped lung depends heavily on the severity of the patient’s symptoms. For individuals who are asymptomatic or have only mild shortness of breath, the condition is managed conservatively with regular monitoring. In these cases, the condition is stable, and the risks of surgical intervention may outweigh the potential benefits.
For patients whose quality of life is significantly affected by severe or progressive shortness of breath, the definitive treatment is a surgical procedure called pleural decortication. This operation involves surgically peeling away the entire restrictive fibrous rind from the surface of the visceral pleura. The goal of removing this non-elastic layer is to allow the underlying lung to fully re-expand and resume its normal function.
Decortication can be performed through an open incision (thoracotomy) or using minimally invasive techniques, such as Video-Assisted Thoracoscopic Surgery (VATS). Following a successful procedure, patients typically spend several days in the hospital, often with chest drainage tubes. Many patients experience a significant improvement in their breathing capacity and overall lung function, leading to a better prognosis and a return to normal activity levels.