Pericardial Fluid: Location, Volume, Composition, and Clinical Significance

The pericardial sac (parietal + visceral pericardium) contains 15–50 mL of serous fluid—an ultrafiltrate of plasma.

Functions

• Lubrication: Reduces friction between visceral and parietal layers during cardiac contraction/relaxation.
• Mechanical protection: Cushions heart; limits excessive dilation.
• Barrier: Limits spread of infection/malignancy from adjacent structures.
• Physiologic reserve: Accommodates acute volume changes (e.g., exercise).

Composition

• Similar to plasma but lower protein (1–2 g/dL), high lactate dehydrogenase (LDH).
• Lymphocytes predominant if inflammatory.

Pathology: Pericardial Effusion

• >50 mL: Detectable on echo (small).
• >250 mL: Cardiomegaly on CXR.
• Rapid accumulation (even 100–150 mL): Tamponade (↑ intrapericardial pressure → ↓ filling → shock).
• Causes: Viral, uremic, malignant, autoimmune, post-cardiac injury, bacterial, TB, hypothyroid, drugs.

Diagnostic Tap (Pericardiocentesis)

• Cell count, cultures, cytology, ADA (TB), tumor markers, pH/glucose.
• Transudate vs. exudate (Light's criteria adapted).

Normal pericardial fluid is essential for cardiac mechanics; excess threatens hemodynamics.