Pleural Effusion

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A pleural effusion is the accumulation of fluid in the pleural space. When excess fluid accumulates, it can impair lung expansion and cause symptoms such as dyspnea, cough, and pleuritic chest pain. POCUS is sensitive for detecting pleural effusions and can guide thoracentesis by identifying the largest fluid pocket and helping to avoid complications.

Pleural effusions are commonly classified as:

• Transudative: Caused by imbalance in hydrostatic and oncotic pressures, leading to fluid accumulation without pleural inflammation. The pleural membranes remain intact, and the fluid is typically clear and low in protein (ie heart failure, cirrhosis, nephrotic syndrome). 
• Exudative: Caused by inflammation, infection, or malignancy affecting the pleura, leading to increased capillary permeability or impaired lymphatic drainage. This allows proteins, LDH, and inflammatory cells to leak (ie infection, inflammatory disease, malignancy) 

An effusion is exudative if any criteria are met; if none, it is likely transudative.

• Pleural fluid protein / serum protein > 0.5
• Pleural fluid LDH / serum LDH > 0.6 
• Pleural fluid LDH > 2/3 of the upper limit of normal serum LDH 

⚠️ Lights criteria will misrepresent 15-30% of true transudates as exudates.