Pleural Effusions
Diagnosis and Treatment of Fluid Collections Around the Lung
Certain conditions may result in pleural effusion, the accumulation of fluid in the lung cavity. How does a physician manage this?
The lungs are surrounded by a membrane called the pleura. Normally, there is a small amount of fluid in the pleural space between the lung and the chest wall, acting as a lubricant. This fluid enters the pleural space from the capillaries of the lung and exits into the lymphatic system. When there is excess pleural fluid, it is called a pleural effusion.
Causes
Pleural effusions can result either from decreased clearance of pleural fluid or introduction of excess fluid into the pleural space. Many conditions cause pleural effusions, including but not limited to infections (e.g., tuberculosis), malignant tumors, trauma, congestive heart failure, and rheumatoid arthritis affecting the lung.
There are two types of pleural effusions. One is called a transudate, the result of the fluid portion of the blood seeping through the lung capillaries by pressure. The other is called an exudate, the result of greater leakage through the lung capillaries that also allows large molecules and cells. Certain tests can be done to help categorize a pleural effusion into one of these two categories.
Clinical Presentation
Individuals with pleural effusion may experience shortness of breath, and sometimes chest pain and cough, if there is enough fluid to restrict lung expansion. Physical examination reveals abnormal sounds through the stethoscope and by percussion of the chest surface. The fluid accumulation can easily be seen on an upright chest x-ray, which may be followed by a chest x-ray with the patient lying on the side (lateral decubitus) to see if the pleural effusion layers out as a free-flowing collection or remains in place as a trapped (loculated) collection.
Thoracentesis
Once a pleural effusion has been established, the next step may be to extract it. Generally, the fluid is removed if there is a significant amount present.
A physician performs a procedure called a thoracentesis to remove this fluid. He or she injects local anesthetic into and through the chest wall between the ribs, which minimizes pain during the rest of the procedure and helps the physician estimate the thickness of the chest wall. Next, the physician slowly inserts a needle through the chest wall and advances it until it just enters the pleural cavity, indicated by the ability to remove some fluid with a syringe.
The needle is removed at the same time a plastic catheter is slid into the pleural space. This catheter is connected to a vacuum bottle. The absence of air in the bottle provides suction that pulls the effusion from the pleural space into the bottle. Additional vacuum bottles are used as needed.
Laboratory Tests
Given the many causes of pleural effusion, analyzing the fluid to see if it is a transudate or an exudate can significantly narrow down the diagnosis. Tests on the fluid include lactate dehydrogenase (LDH), total protein, cell count and differential, and bacterial cultures. Additional tests for specific diagnoses may also be ordered as necessary.
Even with some diagnoses eliminated, the physician still needs to look for other symptoms and signs and order more tests to determine which of the remaining causes of pleural effusion is most likely.
Treatment
The thoracentesis serves as a therapeutic measure in addition to a diagnostic one. Besides removing the effusion, the other component of treatment is to address the underlying cause. While this can prevent another effusion, some patients have recurrent pleural effusions and are treated with an indwelling catheter or a procedure to obliterate the pleural space (pleurodesis).
