What causes transudates in pleural effusions (fluid on the lungs)?

Updated: Dec 28, 2018
  • Author: Kamran Boka, MD, MS; Chief Editor: Guy W Soo Hoo, MD, MPH  more...
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Transudates result from an imbalance in oncotic and hydrostatic pressures. Transudative effusions are usually ultrafiltrates of plasma squeezed out of the pleura as a result of an imbalance in hydrostatic and oncotic forces in the chest. However, other mechanisms of injury may include upward movement of fluid from the peritoneal cavity or, in iatrogenic cases, direct infusion into the pleural space from misplaced (or even migrated) central venous catheters or nasogastric feeding tubes.

Transudates are caused by a small, defined group of etiologies, including the following:

  • Congestive heart failure

  • Cirrhosis (hepatic hydrothorax)

  • Atelectasis (may be due to occult malignancy or pulmonary embolism)

  • Hypoalbuminemia

  • Nephrotic syndrome

  • Peritoneal dialysis

  • Myxedema

  • Constrictive pericarditis

  • Urinothorax (usually due to obstructive uropathy)

  • Cerebrospinal fluid (CSF) leaks to the pleura (in the setting of ventriculopleural shunting or of trauma/surgery to the thoracic spine)

  • Duropleural fistula (rare, but may be a complication of spinal cord surgery)

  • Extravascular migration of central venous catheter [7]

  • Glycinothorax (rare complication of bladder irrigation with 1.5% glycine solution following urologic surgery)

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