Transfus？o consciente de hemoderivados. Revis？o sistemática dos fatores indicativos do gatilho para a infus？o dos componentes sanguíneos

background and objectives: with the surgical and anesthetic technology advance the indications for intervention are expanding, as well as the need for blood transfusions. because of its great scientific value, the content to be exposed is subject for endless discussions that provide different guidelines in various clinical and laboratory aspects. the objective of this review is to determine the clinical, laboratorial, and monitoring signs that should guide blood transfusion initiation, avoiding any risk and unnecessary use of resources, as well as the delay on starting therapy, determining tissue hypoxia and its corollaries. content: scientific articles of clinical trials and reviews were used to range various subjects approached in the present content. these subjects were divided according to clinical and laboratorial aspects. once the described search finished, 2,608 papers were identified, but only 17 original references were selected by inclusion criteria. conclusions: literature is unclear about clinical criteria on the ideal moment to begin the transfusion therapy in order to optimize the relations risk/ and cost/benefit. studies show that there is no significant difference of oxygen supply (o2) in a comparison of hemoglobin (hb) levels between 6 and 10 g.dl-1, mainly by reduced blood viscosity, facilitating the vascular flow to tissues. however, there is a tendency to recommend the transfusion trigger (tt) when it reaches low values as 6-7 g.dl-1. this same tendency indicates that red blood cells should never be administered with hb levels > 10 g.dl-1, except in special situations.