[Blood transfusion in anemic patients. When and how?]

The functional red cells infused must breathe and circulate. The effectiveness of transfusion depends on different factors in patients (lack of antibodies or hypersplenism) and on the way the blood has been preserved. The transfusion-related risks may be immediate (immunological conflicts between erythrocytes or leucocytes) or delayed (alloimmunization induced by transfusion, transmission of or viral or parasitic diseases). The current preventive measures are highly efficient, provided all "safety catches" are respected, including selection of donors on immunological and serological grounds, and choice of the red cell concentrate most appropriate to the clinical situation and the transfusional future of the patient. All patients on chronic transfusion must be under long-term surveillance, with search for antibodies and serological profile. The decision to transfuse blood rests on the levels of erythrocyte constants and on clinical tolerance to anaemia, taking into account the compensatory mechanisms. Several formulas are available to calculate the red cell volume to be transfused in relation to haemoglobin values. The advances achieved in blood perfusion are such that anaemic patients nowadays are both less and better transfused.