Serious bleeding (hemorrhage) usually results when an artery or vein is cut or torn (such as being punctured by shrapnel or the sharp end of a fractured bone) or when the blood vessel is ruptured due to disease or a blow with a blunt instrument.
Bleeding may be either external or internal.
a. External Bleeding.
When the bleeding is external, blood can be seen coming from an open (skin is broken) wound.
External bleeding can be from an artery (a blood vessel which carries blood away from the heart), from a vein (a blood vessel which carries blood back to the heart), or from capillaries (tiny blood vessels connecting an artery and a vein).
(1) Arterial blood is bright red (rich in oxygen) and is usually expelled from the wound in spurts. The spurts are caused by the pulse waves resulting from the heart’s pumping actions (contractions).
(2) Venous blood is a dark bluish-red (low in oxygen content) and flows at a slower, steady rate. Venous blood does not escape in spurts because the pulse is not present in the veins.
(3) Capillary blood resembles venous blood in color. The very small size of capillaries causes the escaping blood to ooze from a wound rather than flow at a more rapid rate.
b. Internal Bleeding.
Internal bleeding occurs when the blood from a damaged blood vessel or organ (such as a laceration of the liver) flows into a body cavity or is trapped in the surrounding tissue rather than escaping the body through an open wound.
Internal bleeding can be identified by discolored tissue (bruises), swelling (from blood escaping into surrounding tissue), rigid body cavity (cavity filled with blood), and/or blood escaping through a body orifice such as the mouth, rectum, or vagina. The casualty may cough up blood (hemoptysis), vomit blood (hematemesis), or pass bloody stools (hematochezia). Vomited blood may be bright red or it may be dark and resemble coffee grounds. The stools may be bright red or dark (melena). Blood loss from internal bleeding is just as serious as visible blood loss from external bleeding.