- • Asymptomatic in many cases; pleuritic chest
pain if pleuritis is present; dyspnea if effusion is large.
- • Diminished breath sounds; decreased tactile fremitus;
dullness to percussion; egophony if effusion is large.
- • Radiographic evidence of pleural effusion.
- • Diagnostic findings on thoracentesis.
In the healthy human being the surfaces of the pleural cavity
are coated with a surfactant-containing, hypooncotic fluid that
lubricates, allowing frictionless apposition of the parietal and
visceral pleura during the respiratory cycle. Under normal conditions
approximately 0.2–0.3 mL/kg of pleural fluid is
present in the pleural space. Its continuous turnover represents
a balance between production by the systemic vessels of the pleura
(primarily the capillaries of the less dependent portions of the
parietal pleura) and removal by the pleural lymphatics (largely
in the more dependent portions of the parietal pleura). The rate
of production of pleural fluid under homeostatic conditions is estimated
to be 0.01 mL/kg/h and is governed by the permeability
of the pleural vessels and the balance of hydrostatic and oncotic
gradients across the pleural surfaces. Normal pleural fluid is low
in protein (∼1 g/dL), slightly alkaline
compared to serum, and relatively hypocellular with approximately 2000
white blood cells (WBC)/ μL in a monocyte/macrophage
predominance with 10–20% lymphocytes and a few
granulocytes and erythrocytes.
Pleural effusion is an abnormal collection of fluid in the pleural
space. Effusions, which may arise from a wide variety of pathological
conditions, are typically classified as empyematous, hemorrhagic,
chylous, exudative, or transudative. Whereas the first three categories
denote collections of pus (from thoracic infection), blood (as in
hemothorax), or lipid-rich chyle (from the chylous duct), the last
two represent broader categories of pathogenesis. Exudative effusions
are protein rich and often quite cellular, typically reflecting
inflammatory or infiltrative processes directly affecting the pleura
(such as pneumonia or cancer), whereas transudative effusions are
low-protein, acellular filtrates that usually arise from imbalances
in the body’s hydrostatic and/or oncotic forces
in the setting of otherwise normal pleura (such as occur in congestive
heart failure or nephrotic syndrome). Causes of transudative and
exudative effusions are listed in Table 22–1.
Causes of Transudative and Exudative Pleural Effusions. |Favorite Table|Download (.pdf)
Causes of Transudative and Exudative Pleural Effusions.
|Congestive heart failure||Infection|
|Cirrhosis with ascites||Bacterial|
|Superior vena cava syndrome||Cancer|
|Fontan procedure||metastatic or primary|
|Pulmonary embolism||Postmyocardial infarction syndrome|
|Collagen vascular disease|
|Yellow nail syndrome|
|Chronic atelectasis/trapped lung|
The hallmarks of pleural effusion on physical examination are
diminution of breath ...