Pathophysiology
Clinical meaning
Pericardial effusion is the abnormal accumulation of fluid within the pericardial sac, the double-walled fibroserous membrane surrounding the heart. The normal pericardial space contains 15-50 mL of serous fluid that lubricates the heart during contraction. Effusions develop when fluid production exceeds reabsorption or when pathological processes introduce additional fluid (blood, pus, lymph, or excess serous fluid). The clinical significance depends more on the RATE of accumulation than the volume: rapid accumulation of 150-200 mL can cause cardiac tamponade (life-threatening compression of the heart), while slow accumulation over weeks can allow the pericardium to stretch and accommodate up to 1-2 liters before causing hemodynamic compromise. Common causes include viral pericarditis (most common in young adults), uremia (renal failure), malignancy (lung, breast, lymphoma, melanoma), autoimmune disease (lupus, rheumatoid arthritis), bacterial infection, post-cardiac surgery (Dressler syndrome), hypothyroidism, and trauma. Cardiac tamponade occurs when intrapericardial pressure exceeds right atrial pressure, preventing ventricular filling during diastole. This reduces stroke volume and cardiac output, activating compensatory tachycardia and vasoconstriction. Without drainage, tamponade progresses to cardiogenic shock and death. The practical nurse monitors for signs of tamponade,...