Editing Pericardial effusion/tamponade (section)

== '''Pathophysiology''' ==

* Pressure depends on the amount of fluid and the pericardial pressure-volume relation
** Tamponade can occur acutely with as little as 150-200mL of fluid, but large slowly-accumulating effusions are often well-tolerated
* Main consequence of increased pressure is compression and collapse of right heart, which then leads to left heart underfilling
* Cardiac tamponade - a continuum from an effusion causing minimal effects to circulatory collapse. This can occur once the effusion reduces diastolic filling to the point that cardiac output declines.
** Compensation occurs with increased adrenergic tone and parasympathetic withdrawal, leading to tachycardia, followed eventually by hypotension. 
** Patients who cannot mount an adrenergic response are more susceptible to tamponade
** Cardiac filling pressure is particularly reduced during inspiration
** Very unusual for tamponade to occur without circumferential effusion
* Effusions can be loculated or localised, resulting in regional tamponade,, especially after cardiac surgery