Blood Transfusion, in medicine, the procedure of introducing the blood of a donor or blood predonated by the recipient (autologous transfusion) into the bloodstream. It is a highly effective form of therapy and has saved the lives of incalculable numbers of people suffering from shock, hemorrhage, or blood diseases. Blood transfusion is employed routinely in cases of surgery, trauma, gastrointestinal bleeding, and in childbirths that involve great loss of blood.
In the 17th century, the French physician Jean Baptiste Denis performed the first recorded transfusion by infusing sheep's blood into a human. Most later attempts were unsuccessful. Even when human blood was used, the majority of recipients died because of blood incompatibility. With the discovery of the major blood groups and the introduction of blood typing in the 20th century, transfusion became routinely successful.
Transfusions still tend to cause the development of sensitivity and increase the possibility that the recipient will react to any later transfusions. Transmission of viral hepatitis was a major risk until a method of screening blood for infectivity was developed in the 1960s; some other forms of hepatitis, however, are not detected by this test. In 1985 a test was introduced that screens donated blood for an antigen associated with AIDS, or acquired immunodeficiency syndrome.
For most of this century, transfusion was accomplished with whole blood. Methods of separating blood into its components (see Blood) were devised during the 1960s. Between 1970 and 1980 the use of these blood components became more frequent than the use of whole blood. Replacement with packed red blood cells (concentrated blood cells that have been separated from the blood plasma) is now the preferred treatment for most blood loss caused by injury or surgery.
In some instances the circulating blood volume can be depleted by loss of fluid but little or no loss of red cells. For example, this can occur soon after a severe burn, during peritonitis, and after a limb has suffered a crush injury. The purpose of transfusion in these instances is to bring the amount of circulating fluid back to or toward normal. For such transfusions red blood cells are not necessary; plasma or, better, serum albumin, a plasma derivative, is more appropriate. Fresh-frozen plasma can be stored for as long as a year, but it still has the potential for transmitting hepatitis and is best used only when blood-clotting factors (proteins in the plasma that assist in the clotting process) are needed. Albumin solution, on the other hand, is heat-treated to destroy hepatitis infectivity. It is used in the management of shock and burns, and for some patients with kidney and liver disease. A less pure fraction of plasma called plasma protein fraction can be used for many of the same purposes.
Clotting factors isolated from blood are used to treat some hereditary bleeding disorders such as hemophilia. Patients undergoing chemotherapy for cancer may have too few platelets, small blood components that help prevent or stop bleeding, both separate from and as part of the clotting process; they may be given an infusion of platelets to speed clotting.
Various synthetic plasma substitutes, such as the carbohydrate compound dextran, as well as various saline solutions, have been used in recent years to replenish the blood-fluid level that often falls dangerously low in cases of sudden shock. These substances, called plasma volume expanders, are more readily available than blood products. During the late 1970s, a synthetic blood-carrying substance called Fluosol-DA, a fluorinated hydrocarbon, was successfully used in several patients who could not or, for religious reasons, would not receive transfusions of natural blood products. Research is also being conducted into ways of converting one blood type into another; if developed, this process would help increase the availability of blood products to all patients.
Although blood can be transferred directly, the usual practice for hospitals is to use blood that has been collected earlier and stored in so-called blood banks. The use of stored blood began during World War I (1914-1918), but the first large-scale blood bank was not created until 1937, in Chicago. Many health-care centers now maintain their own blood banks, using more than 98 percent volunteer donors; the American Red Cross also runs a large volunteer program. A donor supplies 480 ml (about 1 pint) each time, and samples are also taken for typing and screening.