Transudative pleural effusions are best described as resulting from which mechanism?

• A. Increased hydrostatic pressure
• B. Infection in the pleural space
• C. Decreased lymphatic clearance of fluid from the pleural space
• D. Bleeding into the pleural space

Answer: (A)

Transudative pleural effusions occur when systemic forces push fluid across the pleural membranes without local inflammation. The best described mechanism is increased hydrostatic pressure in the capillaries, which drives fluid into the pleural space as seen in congestive heart failure. Because this process is noninflammatory, the fluid tends to be low in protein and LDH.

Infection in the pleural space causes an exudative effusion due to inflammation and increased vascular permeability, while impaired lymphatic drainage can contribute to fluid buildup but is associated with higher protein content, and bleeding into the pleural space yields a hemorrhagic effusion rather than a transudate.