The escape of blood from a blood vessel, normally in response to some trauma, or as a result of a clotting disorder such as HAEMOPHILIA. The bleeding may be external and follow, for example, a skin laceration; or it may be internal and result from, for example, HAEMATEMESIS (bleeding into the stomach), HAEMOPTYSIS (bleeding from the lungs), or HAEMATURIA (bleeding from the kidneys or urinary tract).

Bleeding into or around the brain is a major concern following serious head injuries, or in newborn infants as a complication of labour, especially if premature. In haemorrhage from an artery, blood is bright red and appears in spurts (in severe cases the patient may bleed to death within a few minutes). Venous haemorrhage is less serious (unless from torn varicose veins). The blood is dark and wells up gradually into the wound; it is easily stopped by applying external pressure. In capillary haemorrhage, the blood slowly oozes out of the surface of the wound and soon stops spontaneously. Haemorrhage may also be classified as primary, reactionary, and secondary (see WOUNDS). Severe haemorrhage causes SHOCK and ANAEMIA, and blood TRANSFUSION is often required.

When a small artery is cut across, the bleeding stops because of changes that are provoked in the wall of the artery and in the constitution of the blood. Every artery is surrounded by a fibrous sheath, and when cut, the vessel retracts some little distance within this sheath and a blood clot forms, blocking the open end of the vessel (see COAGULATION). When a major blood vessel is torn, such spontaneous closure may be impossible and surgery may be required to stop the bleeding.

Three main principles are applicable in the control of a severe external haemorrhage: (a) direct pressure on the bleeding point or points; (b) elevation of the wounded part; (c) pressure on the main artery of supply to the part.

Control of internal haemorrhage is more difficult than that of external bleeding. First-aid measures should be taken while professional help is sought. The patient should be laid down with legs raised, and he or she should be reassured and kept warm. The mouth may be kept moist but no fluids should be given.