Uses of Blood and Blood Components
Blood can be packaged and kept in blood banks for emergencies. To keep the blood from clotting, a solution such as citrate-phosphate-dextrose-adenine (CPDA-1) is added. The blood may then be stored for up to 35 days. The blood supplies in the bank are dated with an expiration date to prevent the use of blood in which red cells may have disintegrated. Blood banks usually have all types of blood and blood products available. It is important that there be an extra supply of type 0, Rh-negative blood because in an emergency this type can be used for any patient. It is normal procedure to test the recipient and give blood of the same type. A person can donate his or her own blood before undergoing elective (planned) surgery to be used during surgery if needed. This practice eliminates the possibility of incompatibility and of disease transfer as well. Such autologous (self-originating) blood is stored in a blood bank only until the surgery is completed.
Whole Blood Transfusions
The transfer of whole human blood from a healthy person to a patient is often a life-saving process. Whole blood transfusions may be used for any condition in which there is loss of a large volume of blood, for example:
* In the treatment of massive hemorrhage from serious mechanical injuries;
* For blood loss during internal bleeding, as from bleeding ulcers;
* During or after an operation that causes considerable blood loss;
* For blood replacement in the treatment of hemolytic disease of the newborn.
Caution and careful evaluation of the need for a blood transfusion is the rule, however, because of the risk for transfusion reactions and the transmission of viral diseases, particularly hepatitis.
Use of Blood Components
Most often, when some blood ingredient is needed, it is not whole blood but a blood component that is given. Blood can be broken down into its various parts, which may be used for different purposes. A common method for separating the blood plasma from the formed elements is by use of a centrifuge, a machine that spins in a circle at high speed to separate components of a mixture according to density. When a container of blood is spun rapidly, all the formed elements of the blood are pulled into a clump at the bottom of the container. They are thus separated from the plasma, which is less dense. The formed elements may be further separated and used for specific purposes, for example, packed red cells alone or platelets alone. Blood losses to the donor can be minimized by removal of the blood, separation of the desired components, and return of the remainder to the donor. The general term for this procedure is hemapheresis (from the Greek word apheresis meaning “removal”) If the plasma is removed and the formed elements returned to the donor, the procedure is called plasmapheresis.
Figure 9-1 Composition of whole blood. Percentages show the relative proportions of the different components of plasma and formed elements.
Figure 9-4 Granulocytes (A-C) and agranulocytes (D, E). (A) The neutrophil has a large, segmented nucleus. (B) The eosinophil has many bright pink-staining granules. (C) The basophil has large dark blue-staining granules. (D) The lymphocyte has a large undivided nucleus. (E) The monocyte is the largest of the leukocytes.
Use of Plasma Blood plasma alone may be given in an emergency to replace blood volume and prevent circulatory failure (shock). Plasma is especially useful when blood typing and the use of whole blood are not possible, such as in natural disasters or in emergency rescues. Because the red cells have been removed from the plasma, there are no incompatibility problems; plasma can be given to anyone.
Plasma separated from the cellular elements is usually further separated by chemical means into various components, such as plasma protein fraction, serum albumin, immune serum, and clotting factors. The packaged plasma that is currently available is actually plasma protein fraction. Further separation yields serum albumin that is available in solutions of 5% or 25% concentration. In addition to its use in treatment of circulatory shock, these solutions are given when plasma proteins are deficient. They increase the osmotic pressure of the blood and thus draw fluids back into circulation. The use of plasma proteins and serum albumin has increased because these blood components can be treated with heat to prevent transmission of viral diseases. In emergency situations healthcare workers may administer fluids known as plasma expanders. These are cell-free isotonic solutions used to maintain blood fluid volume to prevent circulatory shock. Fresh plasma may be frozen and saved. When frozen plasma is thawed, a white precipitate called cryoprecipitate forms in the bottom of the container. Plasma frozen when it is less than 6 hours old contains all the factors needed for clotting. Cryoprecipitate is especially rich in clotting factor VIII and fibrinogen. These components may be given when there is a special need for these factors. The gamma globulin fraction of the plasma contains antibodies produced by lymphocytes when they come in contact with foreign agents, such as bacteria and viruses. Antibodies play an important role in the immune system. Commercially prepared immune sera are available for administration to patients in immediate need of antibodies, such as infants born to mothers with active hepatitis.