Editing Pleural effusions (section)

== '''Pathophysiology''' ==

* Disrupted balance between fluid production and absorption
** The amount of pleural fluid is controlled by a balance of oncotic and hydrostatic pressure within the pleural space and pleural capillaries
** Under normal circumstances, the net pressure moves fluid from the parietal pleura into the pleural space
** Pleural space normally contains 0.3mL/kg of fluid
** Normal turnover is about 0.15mL/kg/hour
** Most pleural fluid is reabsorbed through lymphatics of the parietal pleura - protein cannot re-enter the relatively impermeable visceral pleura
* Causative factors:
** Increased input:
*** Increased hydrostatic pressure
*** Increased negative intra-pleural pressure
*** Increased capillary permeability
*** Decreased plasma oncotic pressure
** Decreased output:
*** Strong reduction in lymphatic drainage
* A pleural effusion represents a new equilibrium point between pressures acting across compartments - hence a larger imbalance will lead to a larger effusion
* Characterise as transudate or exudate
** Transudates are protein-poor and result in change in fluid balance in the pleural space
** Exudates are protein-rich and may be related to disruption of pleural or lymphatic reabsorption
* Volume
** 300mL of fluid causes blunting of costophrenic angle on upright CXR
** 500mL of fluid can be detected clinically