As smaller PE's tend to lodge in more peripheral areas without collateral circulation they are more likely to cause lung infarction and small effusions, both of which are painful, but not hypoxia, dyspnea or hemodynamic instability such as tachycardia. Larger PE's, which tend to lodge more centrally, typically cause dyspnea, hypoxia, hypotension, tachycardia and syncope, but are often painless because there is no lung infarction due to collateral circulation. The classic presentation for PE with pleuritic pain, dyspnea and tachycardia is most likely to be caused by a large embolism that fragments and thus causes both large and small PEs. Thus small PEs are often missed because they cause pleuritic pain alone without any other findings and large PEs are often missed because they are painless and mimic other conditions often causing EKG changes and small rises in troponin and BNP levels.
