Understanding the Functions and Disorders of the Pleural Fluid

Anatomy and Function of Pleural Fluid and Abnormalities

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If your doctor has mentioned that you have a build-up of pleural fluid or an infection involving your pleural cavity, what does that mean?

What is Pleural Fluid?

Pleural fluid is the fluid that is found between the layers of the pleura, the membranes of which line the cavity and surround the lungs. The space containing the fluid is referred to as the pleural cavity or pleural space. Normal pleural fluid consists of a small amount of a thin (serous) fluid that functions as a lubricant during breathing.

Changes in the volume of pleural fluid can be caused by infection, trauma, or other causes and can lead to respiratory problems and other adverse conditions. Extraction of pleural fluid allows us to diagnose causes of these changes or to investigate for signs of infection or disease. When a large amount of pleural fluid 

Function of Pleural Fluid

Pleural fluid is a thin translucent fluid that fills the cavity between the parietal (outer) and visceral (inner) pleural layers surrounding the lungs. The volume of fluid is small, roughly 20 ccs or 4 teaspoons.

Pleural fluid functions by lubricating the space between the pleura, allowing the pleura to glide smoothly during inhalation and exhalation. In this way, it cushions delicate lung tissues against friction from the ribs and the chest wall itself.

Conditions Involving the Pleural Cavity

There are several conditions that can affect the pleural cavity and, by default, the pleural fluid.

Among these:

  • Pleural effusion is a condition wherein excess fluid accumulates in the pleural space. There are many causes of pleural effusions, including congestive heart failure, pulmonary embolism, kidney conditions, cancer, and autoimmune diseases such as lupus and rheumatoid arthritis. Over 200,000 people in the U.S. are affected by pleural effusion each year.
  • When a buildup of fluid contains cancer cells, it is called a malignant pleural effusion. While this most commonly occurs with during stage 4 lung cancer, it can also occur with other cancers that have spread (metastasized) from other parts of the body, including the breast and ovaries.

Symptoms and Diagnosis of Pleural Disorders

When fluid builds up in the pleural space, it can compress the underlying lung. This, in turn, can cause shortness of breath, chest pain, and other symptoms of respiratory distress.

To investigate, a doctor will extract pleural fluid using a number of standard procedures:

  • Thoracentesis(also called a needle aspiration) extracts pleural fluid by inserting a needle through into the pleural space, the sample of which can then be analyzed in the lab.

Upon extraction of pleural fluids, samples can be evaluated to ascertain the causes of any changes or to confirm the presence of an infection or disease. The two main methods of analysis include:

  • Pleural fluid analysis is a procedure in which fluid obtained via thoracentesis is examined for both its consistency and substances such as protein. There are two primary types of pleural fluid found in pleural effusions. One is a transudate, which is a thin, clear fluid most commonly seen in congestive heart failure. The other is an exudate, a thicker, pus-like fluid more frequently found during an infection.
  • Pleural fluid cytology is a process that aims to detect the presence of certain white blood cells (their presence of which would indicate an infection), bacteria (using a gram stain), and other substances that shouldn’t be there. If an infection is suspected, the fluid would then be cultured to identify the specific infective agent.

Treatment of Pleural Fluid Disorders

If excess pleural fluid accumulates in the pleural space, it can result in increasing shortness of breath, chest pain (often worsening with a deep breath,) and may eventually compress the heart leading to heart failure.

To remove the fluid, a chest tube is usually placed.

 Chest tube placement involves the insertion of a flexible tube into the pleural space. The tube may be left in place to drain excess fluid, blood, or air which has accumulated. It can be kept in place for varying amounts of time depending on the condition or cause.

Sometimes, fluid continues to accumulate, making it difficult to remove the chest tube. There are a few procedures which can be done if this occurs. In a pleurodesis, the two membranes of the pleura are forced to adhere to each other by injecting a chemical (such as talc) into the pleural space. This creates inflammation and eventually scarring which serves to glue the two layers of the pleura together, obliterating the pleural space.

Another option is to place a stent into the pleural space which is connected to the outside of the body. The fluid can then be withdrawn periodically, even in the comfort of your home. This is done most often for pleural effusions related to advanced cancer.

Finally, a pleurectomy may be performed. In this procedure the pleural membranes are removed, effectively removing the pleural space.

Sources

  • American Society of Clinical Oncology. “Fluid Around the Lungs or Malignant Pleural Effusion.” Alexandria, Virginia; August 2016.
  • Dixon, G.; de Fonseka, D.; and N. Maskell. “Pleural controversies: image-guided biopsy vs. thoracoscopy for undiagnosed pleural effusions?” Journal of Thoracic Disease. 2015; 7(6):1041-51.
  • U.S. National Library of Medicine. “Pleural Fluid Analysis.” MedlinePlus. Bethesda, Maryland; Updated 11/19/15.

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