Hemorrhage

Hemorrhage is the loss of blood from the circulation through a damaged vessel. It may be external, through a wound or a body opening, or internal, into tissues, organs or body cavities, where it can go unseen. Injury is the most common cause, but bleeding also results from diseases that erode vessels, such as ulcers and tumors, from burst aneurysms and fragile vessel walls, and from failures of hemostasis, as in hemophilia, a low platelet count or treatment with anticoagulant drugs.

Bleeding into tissue has specific names by size and form: pinpoint red dots in the skin are petechiae, larger flat patches are purpura and bruises (ecchymoses), and a collection of clotted blood is a hematoma. Location can matter more than amount: a small hemorrhage inside the skull can compress the brain, as in a hemorrhagic stroke. Large or rapid blood loss shrinks the volume of blood the heart can pump. The body responds with a racing pulse and narrowed blood vessels, but if bleeding continues, blood pressure falls and hemorrhagic shock follows, starving organs of oxygen.

Treatment first aims to stop the bleeding, with pressure, tourniquets, surgery or endoscopic and radiological procedures, and then to replace lost volume with fluids and blood transfusion. Slow, long-term bleeding, for example from the gut, can instead cause iron deficiency anemia.