Pleural Effusion

Home » Pleural Effusion » Overview

Questions to Ask Your Pulmonary Care Team
(Free Handout)

Overview

Fluid that accumulates in the pleural space because of trauma or disease is called pleural effusion. This condition may result from heart failure, cancer, pulmonary embolism, or inflammation. If blood is in the accumulating fluid, the condition is called "hemothorax"; if pus is present, it is called "empyema"; if air enters the space, it is called "pneumothorax"; and if there is chyle (milky fluid consisting of lymph and fat), it is called "chylothorax." There are two types of pleural effusion, transudative and exudative.

An imbalance between the venous-arterial pressure and the pressure within the pleural space (oncotic pressure) causes transudative effusions. Transudates contain few protein cells and little solid material content and have a clear, pale yellow color. Cardiac failure and, less commonly, liver and kidney disease cause transudative pleural effusion.

Exudative effusions are caused by inflammation, infection, and cancer. Exudates have large amounts of protein cells, white blood cells, and immune cells that have migrated into the pleural fluid and deposited in tissues or on tissue surfaces. Exudates also are pale yellow in color but have a cloudy appearance. If pus is present because of infection (empyema), the fluid is yellow, cloudy, and has a foul odor. Pneumonia, tuberculosis, pulmonary embolism (blocked pulmonary artery), cancer, and trauma are common causes of exudative pleural effusion.

The Pleural Space
A shiny, thin, transparent membrane called the serous coat, or pleura, covers each lung. The inner (visceral) layer of the pleura is attached to the lungs and the outer (parietal) layer is attached to the chest wall. Both layers are covered with mesothelial cells, which secrete a small amount of fluid (i.e., less than 2 tablespoons) that provides lubrication between the chest wall and the lung. Both layers are held in place by a film of pleural fluid, like two glass microscope slides that are wetted and stuck together. The pleural space is called a potential space because it is virtually nonexistent. The pleural membranes prevent the lung from making direct contact with the chest wall and the diaphragm. Cells in the pleural space are primarily mesothelial cells that line the surfaces of the pleural membranes and some white blood cells.

The pleural membranes are semipermeable. A small amount of fluid continuously seeps out of the blood vessels through the parietal pleura. The visceral pleura absorbs fluid, which then drains into the lymphatic system and returns to the blood. Protein in the circulation and balanced pressures keep excessive amounts of fluid from seeping out of the blood vessels into the pleural space.

Mechanisms of Pleural Fluid Accumulation
An excessive amount of pleural fluid probably results from a combination of fluid draining into the tissues from the blood vessels and the overproduction of fluid by the mesothelial cells. Fluid accumulates in the pleural space by three mechanisms: increased drainage of fluid into the space, increased production of fluid by cells in the space, and decreased drainage of fluid from the space.

Increased amounts of fluid drain from the circulation when there is hypertension in the venous system (creating pressure imbalance) or when there is too little protein in the blood. Ascites (fluid in the peritoneal space, or abdominal cavity) can drain through small perforations in the diaphragm. A large amount of fluid can drain directly into the pleural space this way.

Abnormal mesothelial cells (as in asbestosis) can produce large amounts of fluid. White blood cells can accumulate in response to infection and inflammation in the pleural space (empyema). These cells produce fluid that is difficult to drain or that are in such large quantities that normal drainage through the lymphatic system simply cannot keep up.

Malignant tumor cells can migrate (or metastasize) to the pleural space from essentially any type of tumor in the body. These cells can attach to either the visceral or parietal pleural surfaces or float freely in the pleural space and produce large amounts of fluid.

When tumor cells block lymphatic drainage, fluid accumulates. If the blockage is located in the central lymphatic drainage system that drains chyle (milky fluid consisting of lymph and fat) to the thoracic duct, fluid rich in chyle accumulates in the pleural space.

© 1998-2008 Healthcommunities.com, Inc. All Rights Reserved.

Pleural Effusion Resources

	Join Our Pleural Effusion Forum Do you have a question, want to share medical advice, or just need to discuss your situation with someone else having a similar experience? The healthchannels forum is a resource for everyone to share and discuss their health and medical needs with others.	Advertising Disclaimer
	Living with...Share your story Do you have a personal health story that you would like to share with others? As a source of free patient education, our goal is to provide our users with trustworthy information and support from others. That's why we've started our "Living with..." sections.
	Our "Living With..." support pages are a place to share experiences about living with a certain condition, disease, disorder, or illness and for loved ones of those dealing with health-related issues. Many people, especially when newly diagnosed, find comfort in knowing that others are having a similar experience. Help others by sharing your story. View stories already submitted.
	Stay Updated Sign up for our newsletter and receive important updates on the medical conditions that are most important to you.
Are you interested in becoming a nurse? Take this test. Advertising Disclaimer To quickly access health information from your website's browser, download Healthcommunities.com's healthchannels toolbar. Advertising Disclaimer