Item 2 of 2
On physical examination, jugular venous pressure is elevated, breath sounds are decreased at the right lung base with dullness to percussion, and 2+ bilateral lower extremity pitting edema is present. Chest x-ray shows cephalization of the blood vessels, Kerley B lines, and a right pleural effusion. Thoracentesis is performed for pleural fluid analysis. In comparison to plasma fluid, which of the following pleural fluid findings is most likely to be observed?
Exudative & transudative pleural effusions | ||
Exudate | Transudate | |
Light criteria | Pleural protein/serum protein >0.5 OR | Exudate criteria not met |
Pathophysiology | Inflammatory increase | Change in hydrostatic or oncotic pressure |
Common causes |
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LDH = lactate dehydrogenase; TB = tuberculosis. | ||
In determining the etiology of a pleural effusion, differentiating whether the effusion is transudative or exudative is an important step. The Light criteria allows differentiation of these two types of effusion via analysis of the protein and lactate dehydrogenase levels of the fluid.
Transudative pleural effusions form due to an imbalance in hydrostatic or oncotic pressure. Heart failure causes increased hydrostatic pressure in the pulmonary circulation due to backup of blood flow from the failing left ventricle. This increased pressure leads to leakage of fluid from the pulmonary capillaries and causes a transudative pleural effusion, which is characterized by low protein and low lactate dehydrogenase levels compared to serum values.
In contrast, exudative effusions result from inflammatory disruption of vascular permeability (eg, infection, malignancy) and demonstrate high protein levels (Choice B) due to increased capillary permeability and reduced sieving of proteins as fluid traverses the capillary wall. Lactate dehydrogenase levels also tend to be high in exudative effusions.
(Choice A) High amylase content is suggestive of a pleural effusion due to pancreatitis, pancreatic pseudocyst, or esophageal rupture.
(Choice C) High leukocyte count is typical of a complicated parapneumonic effusion or some types of malignant pleural effusion. Transudative effusions do not demonstrate high leukocyte counts.
(Choice D) Low glucose content is seen in the setting of malignant or infectious pleural effusion due to consumption of glucose by bacteria, neutrophils, and/or malignant cells.
Educational objective:
Heart failure can cause transudative pleural effusion due to an increase in pulmonary capillary hydrostatic pressure. Light criteria are useful to differentiate transudative and exudative pleural effusions; transudative effusions are characterized by low protein and lactate dehydrogenase content compared to serum values.