BLOOD TRANSFUSION

the transfer of blood into the vein of a human or animal recipient. The blood is either taken directly from a donor or is obtained from a blood bank. Blood transfusions are a therapeutic measure used to restore blood or plasma volume after extensive hemorrhage, burns, or trauma; to increase the number and concentration of red blood cells in persons with anemia in order to improve the oxygen-carrying capacity of their blood; and to combat shock. Transfusions are a crucial adjunct in some types of surgery in which patients lose large amounts of whole blood that must be replaced. The first documented records of intravenous blood transfusions date from Europe about the mid-17th century, but so many patients died from the resulting incompatibility reactions that the process was banned in France, England, and Italy late in the century. Transfusion, which is now a frequent and lifesaving procedure, could not become useful or safe until the blood-group antigens and antibodies were discovered; the first system to be identified was the ABO blood group system in 1901. Thereafter, the routine blood typing of donors and recipients permitted successful transfusions of blood between them. The actual procedure for transfusing blood is simple and straightforward. A pint or more of blood is withdrawn from a donor's arm vein by means of a hypodermic syringe and is passed through a plastic tube to a collection bag or bottle to which sodium citrate has been added in order to prevent the blood from clotting. In transfusing blood into the recipient, donor blood of the appropriate type is passed by gravity from a container down through a plastic tube and into a vein of the recipient's arm. The procedure is accomplished slowly, and two hours may be needed to infuse a pint of blood into the recipient. The use of sterile containers, tubing, and needles helps ensure that transfused or stored blood is not exposed to disease-causing microorganisms. Blood can be kept in a state satisfactory for use in transfusion by the addition of special preservatives and refrigeration for up to 35 days, and methods of fractionating the blood have allowed its use in specialized form. Transfusions of whole blood or of blood fractions are used to treat at least 10 different conditions: (1) whole blood, which is used to treat acute blood loss; (2) packed red cells, which are used for chronic anemia; (3) washed red cells for allergies that have been induced in frequently transfused patients by other elements in the blood; (4) platelets for bleeding caused by platelet deficiency; (5) white cells for low white-cell count in patients with infections; (6) plasma for shock without blood loss; (7) fresh-frozen plasma, freshly drawn plasma, or concentrates of the antihemophilic factor of plasma for bleeding in hemophilia; (8) albumin, concentrated from the plasma, for shock or for chronic low-albumin disorders and malnutrition; (9) gamma globulin, the antibody component of the plasma, concentrated for prevention of viral hepatitis and protection against or modification of measles after exposure; (10) fibrinogen, an important clotting factor in the blood, easily concentrated for bleeding conditions brought about by deficiency or absence of fibrinogen. Exchange transfusion, in which all or most of the patient's blood is removed while new blood is simultaneously transfused, is of use in combatting erythroblastosis fetalis, removing certain poisons, and producing transient improvement in leukemics. Undesirable reactions to transfusion are not uncommon and may occur for many reasons, such as allergy, sensitivity to donor leukocytes, or undetected red-cell incompatibility. Unexplained reactions are also fairly common. Rare causes of transfusion reaction include contaminated blood, air bubbles in the blood, overloading of the circulatory system through administration of excess blood, or sensitivity to donor plasma or platelets.