00:00 / 00:00
Normally, this space contains 20 to 25 milliliters of fluid that provides lubrication, allowing the two pleural layers to slide over each other during breathing. This pleural fluid forms as a filtrate from pleural blood vessels. At the same time, it is drained into the lymphatic vessels, and this allows for regular renewal of the fluid.
Now, pleural effusion is typically caused by increased production or impaired drainage of the pleural fluid. Depending on the cause, the excess fluid in pleural effusion can be protein-poor, called transudate, or protein-rich, called exudate.
Transudate, also called hydrothorax when it involves the pleural space, forms when too much fluid starts to move from the pulmonary capillaries into the pleural space, either because of increased hydrostatic pressure or decreased oncotic pressure within the pulmonary capillaries. So increased hydrostatic pressure occurs usually in the context of heart failure, where the heart can’t pump blood effectively, so it backs up into the pulmonary vessels, leading to pulmonary hypertension; ultimately, the high pressure forces fluid out of the pulmonary capillaries and into the pleural space. On the other hand, decreased oncotic pressure can be caused by cirrhosis, which leads to decreased hepatic production of plasma proteins like albumin; or nephrotic syndrome, where renal filtration of blood is impaired, so the proteins are lost in urine.
Copyright © 2023 Elsevier, its licensors, and contributors. All rights are reserved, including those for text and data mining, AI training, and similar technologies.
Cookies are used by this site.
USMLE® is a joint program of the Federation of State Medical Boards (FSMB) and the National Board of Medical Examiners (NBME). COMLEX-USA® is a registered trademark of The National Board of Osteopathic Medical Examiners, Inc. NCLEX-RN® is a registered trademark of the National Council of State Boards of Nursing, Inc. Test names and other trademarks are the property of the respective trademark holders. None of the trademark holders are endorsed by nor affiliated with Osmosis or this website.