There are only 2 reasons to do pericardiocentesis: to relieve tamponade and to diagnose fluid by retrieving some for the lab.
Conditions that cause pericardial effusion are: trauma (e.g. Blood), infection (e.g. Tb or viral), malignancy (e.g. Breast or lung cancer), thyroid deficiency, uremia, collagen vascular disease (e.g. Lupus). This is not a complete list but covers the most common causes.
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