What is Trapped Lung?
Non-expandable lung, often abbreviated as NEL, is a term for conditions where the lung isn’t able to fully expand into the chest cavity or the space around the lung called the pleural space. There are three main causes of NEL: a) an obstruction in the bronchus, the large airway leading to different parts of the lung, causes the nearby lung tissues to collapse, b) chronic atelectasis, which is a long-term condition where the lungs don’t fill with air properly, and c) restriction of the lung due to diseases affecting the lung’s surrounding cover, a condition known as a trapped lung.
The term “trapped lung” was first coined in 1967; it describes a condition where a band of tough tissue, caused by inflammation, wraps around the lung cover, making it hard for the lung to fully expand. The inflammation is usually caused by lung infections like pneumonia or a condition called hemothorax where blood accumulates in the pleural space. Other causes include a collapsed lung, surgeries in the chest area, a condition caused by high levels of toxins in the blood called uremia, and autoimmune diseases like rheumatoid pleuritis which is inflammation of the lung cover.
In everyday health care settings, a person with a trapped lung often has a chronic build-up of fluid in the pleural space, known as pleural effusion. If the fluid is frequently drained without any improvement in lung expansion, it can lead to unwanted side effects.
What Causes Trapped Lung?
In the past, treatment for a lung condition called pneumothorax, specifically for tuberculosis, often resulted in another condition called trapped lung. Trapped lung can be caused by several diseases and conditions. These include conditions related to the immune system like rheumatoid pleurisy, inflammatory pleuritis, and also conditions like improperly drained blood in the chest (hemothorax), and fluid around the lungs due to pneumonia (parapneumonic effusions).
Trapped lung can also be caused by infections, such as bacterial empyema, tuberculous pleurisy, and when there’s a buildup of fluid in the lung due to cancer (malignant pleural effusions). Exposure to asbestos, a condition related to kidney failure called uremic pleurisy, surgery on the heart, radiation treatment for the chest, and certain medications can also trigger trapped lung.
Understanding what causes trapped lung is crucial because it helps doctors identify the right treatment methods for each individual case. The cause often determines the best way to relieve the symptoms and prevent the condition from worsening. So, always provide your complete medical history to your doctor for accurate diagnosis and effective treatment.
Risk Factors and Frequency for Trapped Lung
Why some people with inflammation in the pleural (the space between the lungs and the chest wall) recover without complications and why others develop scarring that restricts lung function is not well understood. This condition, where the lung becomes ‘trapped’, is likely more common than we realize. A study showed that of people who had a procedure to draw fluid from the pleural (known as thoracentesis):
- About 10% had a ‘non-expandable’ lung – a lung that can’t fully inflate.
- About 20% of those who underwent therapeutic thoracentesis – a similar procedure, but for treatment purposes rather than diagnosis – also had a ‘non-expandable’ lung.
- This number rose to 30% for those who had therapeutic thoracentesis to treat a condition called ‘malignant pleural effusion’ – a build-up of fluid in the pleural due to cancer.
Signs and Symptoms of Trapped Lung
Pleural effusion, a condition where there is excess fluid in the layer of tissue that lines the lungs and chest cavity, can present differently depending on its size. Small effusions might not cause any symptoms, and may only be discovered through chest scans or x-rays. However, with larger effusions, one might notice symptoms like reduced breath sounds on one side, an unusual dullness when the chest is tapped, and decreased vibration sense.
When the condition gets severe, it can cause difficulty in breathing which demands immediate treatment. This treatment might involve removing the excess fluid through a process called thoracentesis or through surgery. During thoracentesis, patients might feel discomfort due to the reduced pressure within the chest.
Another condition called lung entrapment can also occur. This is because of an active inflammation process which can cause chest pain and severe difficulty in breathing. This condition can complicate the situation if not diagnosed and treated properly, leading to inadvertent diagnostic and therapeutic procedures that might result to more complications. Therefore, it is important for health practitioners to consider lung entrapment when diagnosing any chronic stable pleural effusion case where no other obvious active disease is found.
Testing for Trapped Lung
If you have a condition called a trapped lung, the fluid analysis of the lining around your lungs (pleural fluid) shows features similar to surplus fluid collection (transudate) or unusual protein-rich fluid (protein-discordant exudate). This fluid usually has a low number of certain immune cells (mononuclear cells). The activity of an enzyme (lactate dehydrogenase or LDH) in this fluid is typically low, and the protein content might be unusually high. However, this raised protein level does not mean you have pleural inflammation or cancer and it doesn’t rule out trapped lung.
A particular sign of having a trapped lung is that the surplus fluid around your lungs (pleural effusion) tends to build up quickly even after it has been drained (thoracocenteses). If you’ve had certain lung conditions in the past like pneumonia, a collapsed lung (pneumothorax), lung surgery, or blood in the chest (hemothorax), and are living with a chronic stable pleural effusion, your doctor might suspect that you have a trapped lung.
Repeated drainage of the fluid around your lungs can lead to complications such as chest pain, scar-like tissue formation in the chest (loculations), bleeding, hemothorax, and recurrent fluid buildup. So, doctors need to stay alert, particularly if you also have cancer-related pleural effusion, to avoid unnecessary draining and complications.
Pleural Manometry is a procedure that can help diagnose a trapped lung by measuring pressure during fluid drainage from your chest. However, because this process takes some time and requires expertise, it’s not regularly used. If a trapped lung is present, the pressure in your pleural space is low and it drops significantly when fluid is removed. These pressure changes are typical of a trapped lung and can assist in diagnosing the condition, especially in patients with minimal or no symptoms. But for solid confirmation, a video-assisted thoracoscopy – a small camera inserted into the chest – or a CT scan that shows a thickening of the lining separating your lung from your chest wall (a pleural rind) is required.
Imaging like upright and decubitus X-rays and CT scans often show a thickening of the pleural layer and unusual tissue formations (loculations). The fluid around your lungs might shift a bit with changes in body position, but will not flow freely. Reduced volume of the half of the chest with pleural effusion compared to the other side suggests a trapped lung.
An ultrasound can also be used for diagnosing trapped lung and should be performed before any pleural intervention. If your ultrasound shows a lack of particular wave-like pattern, known as the “absent sinusoid sign,” it suggests an unexpandable lung, matching the findings of pleural manometry. Apart from this, an ultrasound of the chest can be useful to distinguish between cancerous and non-cancerous diseases, thickening of the pleura, nodules, and a consolidated lung with or without effusion.
Treatment Options for Trapped Lung
When a person has a medical condition known as trapped lung, there are several possible treatments. The choice of treatment often depends on the symptoms someone is experiencing. If there are no symptoms and the condition doesn’t seem to be getting worse, doctors might choose to just monitor the situation.
If the patient is experiencing shortness of breath, which is caused by fluid buildup in the space surrounding the lungs (pleural effusion), they might need a procedure called thoracentesis to remove this fluid. In patients who are not expected to live long due to severe illness, they might have this procedure often to alleviate their symptoms. Alternatively, a pleural catheter, a small, flexible tube, can be inserted into the fluid-filled space to help ease symptoms. This technique is minimally invasive and can provide immediate relief. However, it could be associated with complications such as rapid fluid buildup, risk of infection, and bleeding.
Pleurodesis, a procedure in which a doctor tries to seal the space around the lungs to help stop the buildup of fluid, is typically not recommended for patients with a trapped lung. Instead, these patients might consider having a specialised catheter known as a chronic indwelling pleural catheter. This flexible tube is meant to help some air get into the lungs, which can help alleviate shortness of breath.
There’s also a technique called a pleuroperitoneal shunt that was first suggested in the 1980s. It involves transferring fluid from around the lungs to the abdominal cavity, but complications like shunt failure and infection make it a less-preferred option.
When it comes to long-term solutions, a surgical procedure known as decortication could be recommended. This involves removing a thickened layer from the surface of the lungs to help them expand more fully, which can help with symptoms of shortness of breath and chest pain, and prevent recurrent pleural effusions. Before this surgery is performed, it’s important to rule out other diseases and conditions that might affect the heart and lungs. This surgery can be done via an open incision (thoracotomy) or in a less invasive way using video-assisted thoracoscopic surgery (VATS). VATS involves using small instruments and a tiny camera to perform the surgery through small incisions in the chest.
For certain situations, medication that breaks down proteins involved in blood clotting (fibrinolytic drugs) may be used. These are introduced into the pleural space to help clear obstruction and promote lung expansion.
However, all of these treatment options essentially ease symptoms rather than curing the condition. When the lung has been trapped in this way for a long time, even after removal of the fibrous tissue, it can be difficult for the lung to fully re-expand.
What else can Trapped Lung be?
It’s crucial to distinguish between a “trapped lung” and “lung entrapment”. That’s because potential treatments differ and unnecessary exams and procedures in patients with a trapped lung can be prevented. The conditions result from different causes; lung entrapment can stem from issues in the pleura (the lining of the lungs) or elsewhere in the body, while trapped lung only arises from problems in the pleura. The elasticity of the lung can increase due to conditions like bronchial obstruction caused by bronchogenic carcinoma (a type of lung cancer) or interstitial diseases such as lymphangitic carcinomatosis, leading to lung entrapment.
When analyzing the fluid in the pleura, patients with lung entrapment usually show exudate (fluid that leaks out due to inflammation), while patients with a trapped lung typically have transudate (fluid pushed through the capillary due to high pressure within the blood vessels) or exudate with lots of mononuclear cells (a type of white blood cell). These two conditions could also be told apart by looking at the elasticity of the pleura. In lung entrapment, the pleura’s elasticity remains normal when some fluid is removed, but the lung doesn’t fully expand as more fluid gets drained, and the elasticity curve steepens. While lung entrapment often resolves as inflammation subsides, this is not the case with a trapped lung. Therefore, these two conditions can be seen as different stages of the same process.
The conditions that may also be considered by doctors when diagnosing these lung conditions include:
- Pneumothorax ex-vacuo (especially collapse of the upper right section of the lung)
- Cryptogenic organizing pneumonia (a type of pneumonia)
- Chronic lung consolidations (areas of the lung filled with fluid)
- Bronchiolitis obliterans organizing pneumonia (a lung condition affecting the bronchioles and alveoli).
What to expect with Trapped Lung
Having a condition known as trapped lung, where the lung is unable to fully expand, has been identified as a factor that can shorten the lifespan of patients living with mesothelioma, which is a type of cancer that occurs in the lining of the lungs. In a study of 229 patients, researchers Bibby and his colleagues discovered that about 33% of patients with Malignant Pleural Mesothelioma, the most common type of mesothelioma, had a trapped lung.
More importantly, they were the first to find that trapped lung on its own predicted a shorter lifespan for these patients. At the moment, why this is the case is not fully understood. Therefore, more research is necessary to provide a clear explanation.
Possible Complications When Diagnosed with Trapped Lung
A trapped lung, when it is left undiagnosed, often displays as an ongoing and stable build-up of fluid in the pleural space, which is the area between the lungs and the chest wall. Individuals with this condition might have to undergo numerous procedures, where fluid is removed from the chest, called thoracocenteses. However, these procedures usually do not yield any significant improvements in breathing symptoms. Multiple thoracocenteses can result in many negative consequences, including undesirable effects caused by the procedure itself, delay in finding out the correct diagnosis and receiving suitable treatment, inefficient use of medical resources, aggravation of the existing disease, and most importantly, substantial discomfort for the patient.
Common Consequences of Multiple Thoracocenteses:
- Deleterious effects associated with the procedure
- Delay in reaching the exact diagnosis and receiving proper treatment
- Inefficient use of healthcare resources
- Deterioration of the pre-existing disease
- Substantial discomfort for the patient
Preventing Trapped Lung
Patients with a condition known as “trapped lung” often face a main risk of undergoing multiple tests and treatments for a persistent fluid collection in the chest, known as a “pleural effusion.” Awareness of this condition can prevent these unnecessary procedures. It’s crucial for these patients to understand that once any underlying serious illnesses like cancer are ruled out, a trapped lung is typically harmless and it’s a long-lasting abnormality of the chest cavity. The need for further tests or treatments should be reduced unless the pictures captured by an x-ray show some changes. By educating patients about their condition, we can help them reduce the chances of undergoing unnecessary future tests or treatments.
