Pleural Effusion -Etiology, Pathogenesis and Types – howMed

a. Increased hydrostatic pressure in visceral pleura

b. Decreased oncotic pressure

c. Onstruction of lymphatic drainage from the visceral pleura

d. Increased vessel permeability of visceral pleural capillaries

Pulmonary infarction, pneumonia

e. Metastasis to the pleura

Types of Pleural Effusion

1. Transudates

Transudate is the ultrafiltrate of plasma involving disturbances in Starling pressures. Examples include:

i. Increased hydrostatic pressure in congestive heart failure

ii. Decreased oncotic pressure in nephrotic syndrome

2. Exudates

Exudate is the protein rich and cell rich fluid present due to an increased vessel permeablity in acute inflammation. Examples include cases of pneumonia, tuberculosis, infarction, metastasis.

3. Chylous

Chylous indicates interruption of the thoracic duct.

Etiology

i. Malignancy (most common)

Blocks lymphatic drainage

ii. Trauma

Iatrogenic tear during surgery or pathologic

iii. Turbid, milky appearance

Due to chylomicrons (diet-derived triglyceride
Chylomicrons form a supranate in a test tube after refrigeration

iv. PF triglyceride > 110 mg/dL is diagnostic

4. Pseudochylous

i. Turbid, milky appearance

ii. Caused by inflammation with increasd amount of necrotic debris

PF cholesterol increased

iii. Most commonly caused by rheumatoid lung diseaes

Laboratory distinction of transudates versus exudates

i. Pleural fluid and serum concentration of lactate dehydrogenase (LDH) and protein are most useful.

Ratio of pleural fluid protein and LDH to serum protein and LDH increased sensitivity and specificity

ii. Additional criteria

pH >7.4 indicates a transudate
pH