be donSome clinically healthy individuals may carry infectious agents in Their           blood.The transfusion of blood products obtained from such individuals may result in disease transmission. Hepatitis viruses are the most common agennts transmitted in this way .Other infectious diseases that can be transmitted by the transfusion of blood products include: Cytomegalovirus (CMV) infection , Epstein-Barr infection , malaria , syphilis , AIDS , HTLV.

Testing for HBsAg is performed on all units of blood collected by The Canadian Red Cross Society in Canada. However , a small percentage of hepatitis B carriers are not detected even by the most sensitive tests currently available.

Non-A, Non-B (NANB) hepatitis may be a serious complication of blood transfusion with approximately 30% of affected individuals progressing to chronic hepatitis . Since the introduction of anti-HCV antibody screening of blood(June 1990), the incidence of NANB post-transfusion hepatitis has decreased. It should be remembered , however , that not all hepatitis following transfusion is transfusion-related. All cases of hepatitis suspected of being transfusion-related should be reported to the hospital blood bank. They will then notify the Blood Centre so the donors of the blood units used for that patient can be further tested.

AIDS has been associated with the transfusion of blood products, particularly clotting factor concentrates before AIDS testing was possible. As of November 1, 1985 the CRCS fully
implemented testing of all donated units for antibodies to HIV. No blood or components from units that are anti-HIV positive are issued for transfusion. In very rare instances a unit could contain HIV and be infectious without antibodies to HIV being present. The exposed them to the HIV virus guards against blood being donated during this “window period”. Coagulation factor concentrates produced by plasma fractionation are now treated to inactive HIV and some hepatitis viruses.

b) Septicemia From Infected Blood :

Sterility of a donated blood unit is maintained by thorough skin cleansing of the site of venepuncture  and through the use of closed plastic systems for the collection and preparation of blood components. Nonetheless , approximately 0.3% of blood donations contain a few bacteria,usually normal skin flora. This contamination does not usually cause clinical problems since most blood components are kept at temperatures that inhibit bacterial growth.Bacteria present in platelet concentrates may pose a significant clinical risk, however, since these components are stored at 20-24C , a temperature that permits bacterial proliferation.

When a unit of blood is to be transfused , the system is opened to insert the administration set into the port of the bag and bacteria may be introduced into the system. To minimize the risk of bacterial proliferation, the transfusion of each unit must be completed within four hours of opening the bag.

The infusion of heavily infected blood products may cause sudden hypotension and shock during the transfusion. However , after the infusion of a lightly infected blood product, signs and symptoms may not occur for several  hours. If septicemia is suspected , the transfusion should be stopped immediately and samples from the patient and the blood component sent to the microbiology laboratory for testing . It is important to prevent potential retrograde contamination of the blood bag contents when the intravenous line is withdrawn. Before removing the needle , clamp the tubing both at the bag and just above the needle.

c) Embolism:

 i) Air Embolism : The use of closed plastic systems for the collection of whole blood and for the preparation of blood Components has virtually eliminated air embolism as a complication of blood transfusion. Nonetheless, deaths have occurred when air has been deliberately introduced into the blood bag, or the administration set, to increase the rate of blood flow to the patient. Air should NEVER be introduced into the blood product container or into the administration set, because of the risk of air embolism.

 ii) Particulate Emboli: Cellular debris and small fibrin strands may accumulate during blood storage and could cause emboli in transfused patients. Large aggregates are held back by the standard blood filter through which all blood products should be administered. Micro aggregate filters are not required routinely, even for transfusion of large volumes of blood , since micro emboli are of doubtful clinical importance in most transfusion situations.

d) Overload:

The infusion of blood products can cause fluid overload and electrolyte imbalance. Repeated red cell transfusions can cause iron overload. Circulatory overload occurs when the rate of infusion is excessive for that patient’s cardiovascular status. The use of Red Blood Cells rather than whole Blood reduces the risk of circulatory overload.

During the storage of red cells, various electrolytes, particularly potassium, leak from the red cells into the plasma. The infusion of red cell preparations with a high plasma potassium concentration does not usually cause a clinical problem, except in children, or in patients receiving massive blood transfusions or who are hyperkalemic before transfusion. In selected clinical situations potassium load can be lowered by washing the red cells to remove the plasma and potassium, or by transfusing red cell preparations that have not been stored for long periods.

Iron overload can occur in patients who require multiple  red cell transfusions over an extended period. Each unit of blood contains approximately 250 mg. Of elemental iron . This excess iron accumulates in the liver , heart and in endocrine glands, interfering with their normal function. Chelating agents such as desferrioxamine can be given to the patient to remove the excess iron.

e) Hemorrhagic Diathesis:

Dilution of the patient’s circulating platelets and/or coagulation factors may occur if large volumes of blood with reduced levels of these constituents are transfused. If the patient’s platelets and coagulation factors are at normal levels pre-transfusion, the dilutional effect
of transfusion is not usually of clinical significance. Replacement can be accomplished with platelets and fresh Frozen Plasma if clinically indicated.