Pathophysiology of pleural effusion

Answer 1

The balance of osmotic and hydrostatic pressure in parietal pleural capillaries normally results in fluid movement into the pleural space. Balanced pressures in visceral pleural capillaries promote reabsorption of this fluid. Excessive hydrostatic pressure or decreased osmotic pressure can cause excess fluid to pass across intact capillaries. The result is a transudative pleural effusion, an ultrafiltrate of plasma containing low concentrations of protein.

Exudative pleural effusions result when capillaries exhibit increased permeability with or without changes in hydrostatic and colloid osmotic pressure, allowing protein-rich fluid to leak into the pleural space.

effects depend upon volume, mild doesn`t have any effecet on lung but moderate to severe have compressive effect on lung tissue

Answer 2

To put it simply the pathophysiology of pleural effusions is that the heart isn't pumping efficiently (typically caused by CHF) so the blood backs up from the left atrium and back into the lungs. As pressure increases in the pulmonary vessels fluid is begins to leak from the vessels and begins to collect in the lungs.