Indian Pediatrics 2001; 38: 227-230
Current Practices in Transfusion Medicine
The understanding of the risks of transfusing whole blood in comparison to blood components has led to the establishment of current indications for blood component therapy. Today the role of whole blood trans-fusion in pediatrics is limited; the only indica-tions being neonatal exchange transfusion and during cardiac surgery.
Clinical indications for transfusing packed red blood cells (PRBCs) vary depending on the duration and severity of anemia. In the setting of acute anemia, e.g., following hemorrhage, an estimated blood volume loss of more than 30-40% warrants PRBC transfusion. A pre-viously healthy patient having blood volume loss upto 30-40% can be treated with crystallaoids alone. In the perioperative scenario, patients almost always require PRBC transfusion for hemoglobin levels less than 6 g/dl and rarely when hemoglobin is greater than 10 g/dl. Between 6 and 10 g/dl, transfusion requirements depend on the extent of blood loss and the patientís clinical condition. In children with congenital hemolytic anemias, like sickle cell anemia and thalassemias, the aim is to suppress autologous RBC production by a chronic transfusion program called hyper-transfusion to maintain the hemoglobin levels between 9.5 and 11 g/dl. This is successful in preventing skeletal deformities and extra-medullary hematopoiesis thereby improving quality of life. On the other hand, acquired hemolytic anemias in children are episodic and only occasionally need transfusion support. The hypoproliferative anemias secondary to bone marrow failure syndromes and oncology patients receiving radiation and chemotherapy need PRBC transfusions depending on the patientís clinical condition, the presence or absence of infection and bleeding and the expected recovery time. It is the authorís practice to maintain hemoglobin of more than 8 g/dl in patients receiving radiation and chemotherapy. Neonates with their unique physiological issues present a difficult challenge in laying down indications for PRBC transfusions. The guidelines advocated by the college of American Pathologists can serve as practice parameters for neonatologists(1).
The beneficial effects of platelet trans-fusions in the prevention and control of hemor-rhage have revolutionized the management and outcome of children with thrombocytopenia. It is now well established that prophylactic platelet transfusion is only warranted for platelet counts less than 5000/mm3(2). In thrombocytopenia of decreased production, the presence of fever, infection and minor bleeding moves the platelet transfusion trigger to 10000/mm3. Platelet transfusion have limited use-fulness where platelet destruction either by antibodies or by consumption is the cause of the thrombocytopenia. In life threatening bleeding or surgical patients who begin with an intact hemostatic system, platelet con-centrations are recommended only when platelet count is less than 50000/mm3 and if there is evidence of microvascular bleeding. In congenital conditions of platelet dysfunction, platelet transfusions for a bleeding episode should be advocated only after carefully weigh-ing it against the risk of alloimmunizations. Platelet transfusions are contraindicated in thrombotic thrombo-cytopenic purpura (TTP) and hemolytic uremic syndrome.
With the availability of purified and recombinant coagulation factors the use of fresh frozen plasma (FFP) and cryoprecipitate has markedly declined. The congenital defi-ciencies of factors II, V, X, XI, XIII, Protein C, Protein S and von Willebrand disease (when not responsive to DDAVP) and the acquired coagulation defects as in severe liver disease, disseminated intravascular coagulation and Vitamin K depletion serve as indications for FFP transfusions, either following bleeding or prophylactically for surgery or procedures. Cryo-poor plasma is used for plasma exchange in thrombotic thrombocytopenic purpura and hemolytic uremic syndrome. The use of cryo-precipitate is restricted to the treatment of hypo and dysfibrinogenemias as most patients with hemophilia and von Willebrand disease receive purified factor concentrates.
Granulocyte transfusions though not very popular have specific indications where they can be life saving. Neonates and stem cell transplant patients when severely neutropenic with documented bacterial and fungal infec-tions, benefit from granulocyte transfusions especially if given daily for 3-5 days. Granulo-cytes collected by apheresis from donors stimulated with steroids or colony-stimulating factors yield products containing more than 1.0 ◊ 1010 cells(3).
Apheresis is the selective removal of blood components during the donation process where the remaining elements are recombined and returned to the donor. It is used for the selective collection of platelets, RBCs, plasma or granu-locytes from the donor. Apheresis products have several advantages over those obtained from whole blood donors but are expensive. A single apheresis platelet product is equivalent to approximately 6 units from random donors. Moreover it decreases the exposure to multiple donors and minimizes alloimmunization(4). For alloimmunized patients who are refractory to random all allogeneic platelets, apheresis platelets from an HLA matched donor can achieve satisfactory post transfusion platelet increment.
Autologous transfusions with blood donated in the preoperative period are beneficial for pediatric patients going for major elective surgeries(5). It is also recommended for sibling bone marrow donors who may suffer significant blood loss during marrow harvest. It eliminates the risk of transfusion transmitted diseases and alloimmunization but still caries the risk of bacterial contamination. Designated donations are those where allo-geneic blood or components from a specific donor are Ďdesignatedí for a specific recipient. Examples include blood from an antigen negative donor for a recipient with alloanti-bodies, infant with neonatal thrombocytopenia whose mother can provide platelets, patients awaiting kidney transplants from living donors and multitransfused patients whose family members can provide components. A desig-nated donor can make multiple donations as necessary as long as usual donor requirements are met. Directed donations from blood relatives must be irradiated to prevent transfusion associated graft versus host disease (TAGVHD)(6).
Blood component therapy is not without adverse effects. Over the decades, under-standing the mechanisms of transfusion reactions has enabled us to Ďtreatí blood products appropriately making them safe for use. Transfusion of viable T lymphocytes and their proliferation in the recipients at risk is the primary cause of transfusion associated GVHD. Irradiation of blood inactivates these lymphocytes. These products are thus rendered safe for patients at risk of GVHD including fetuses receiving intrauterine transfusions immunocompromised patients, marrow and organ transplant recipients, and patients receiving HLA matched platelets and recipients of donor units from blood relatives. Leuko-reduction of blood diminishes the chances of alloimmunization to histocompatibility antgens, transmission of viruses, febrile reactions and GVHD(7). Third generation filters currently available provide a 3 log depletion of leuko-cytes to less than 5 ◊ 106 leukocytes/bag to qualify as leucopoor(8).
Leukoreduced PRBCs are indicated to prevent alloimmunization in all patients who need repeated transfusions. These include transfusion dependent hemolytic anemias, bone marrow failure syndromes, hematologic malig-nancies and transplant recipients, patients with recurrent febrile nonhemolytic reactions and as an alternative to CMV negative components.
The infectious disease testing of each unit of blood product includes testing for syphilis, hepatitis B surface antigen, HIV antigen, and antibodies to HIV1, HIV2, hepatitis B core antigen, hepatitis C virus and HTLV I/II. Although, no blood transfusion is absolutely free of the risk of infectious disease transmission, current testing ensures maximum effectiveness of available technology in reducing the risks of blood transfusion.