The obstructing material is most often a blood clot, but may be a fat globule, air bubble, piece of tissue, or clump of bacteria. The symptoms of an embolism usually do not appear until the embolus lodges within a blood vessel and suddenly obstructs the blood flow.
Emboli usually lodge at divisions of an artery, where the vessel narrows.
The signs of obstruction appear almost immediately with severe pain at the site. If the embolus lodges in an extremity the area becomes pale, numb, and cold to the touch, and normal arterial pulse below the site is absent. Fainting, nausea, and vomiting and eventually severe shock may occur if a large vessel is occluded. Unless the obstruction is relieved, gangrene of the adjacent tissues served by the affected vessel develops. In order to prevent the development of emboli it is necessary to avoid venous stasis in patients who are confined to bed because of surgery, illness, or injury.