pleural effusion
Picture each lung wrapped in two thin, slippery sheets with a microscopic film of lubricant between them, letting the lung glide smoothly as you breathe. A pleural effusion is when that film grows into a real puddle — too much fluid collects in the space between the sheets, and the lung no longer has room to expand freely.
The pleural space normally holds only a few milliliters of fluid, continuously produced and reabsorbed. An effusion forms when production outpaces drainage — from raised pressures pushing fluid out (as in heart failure), from low blood protein, or from inflammation, infection or cancer making the surfaces leaky. Large effusions compress the underlying lung and shift the breathing mechanics, causing breathlessness and a dull, dragging chest discomfort.
The first job after finding an effusion is to ask why it is there. A sample is usually drawn with a needle and tested; the results sort the fluid into a transudate (a pressure or protein problem) or an exudate (an inflammatory, infectious or malignant problem), which points to very different causes and treatments. The fluid itself can be drained for relief, but lasting improvement depends on treating the underlying disease.
A patient with known heart failure becomes breathless and a chest film shows fluid at both lung bases; a small sample confirms a transudate, and treating the heart failure with diuretics shrinks the effusions without need for repeated drainage.
A transudative effusion that resolves when its driving pressure problem is treated.
On examination an effusion gives a dull sound to percussion (tapping) and quiet breath sounds over the fluid; a chest film shows blunting of the sharp angle where the diaphragm meets the chest wall. Ultrasound is more sensitive and is now routinely used to guide safe needle placement.