Several aspects of some techniques avoiding homologous blood transfusions

The use of homologous blood products during anesthesia and surgery is not without risks. Complications due to homologous blood transfusions include transfusion reactions, isosensitization, transmission of infections (including HIV, hepatitis, CMV) and immunosuppression (resuiting in increased postoperative infections and possibly increased cancer recurrence). Thus, there are important reasons to try to avoid the transfusion of homologous blood products as much as possible. Several strategies exist which can be employed to decrease the amount of homologous blood products used in a patient perioperatively, including preoperative preoperative autologous blood donation, intraoperative cell saving, several hemodilution techniques and acceptance of a lower hematocrit perioperatively. Preoperative autologous blood donation is only appropriate for elective procedures which can be planned several weeks in advance, without a chance of postponement, and in which an adequate amount of blood loss is anticipated to make the PABO effective. Therefore, this technique can only be used in a limited number of cases. Moreover PABO induces a decrease in natural killer cell activity. The different hemodilution techniques can be subdivided according to certain characteristics, such as preoperative (acute) or peroperative (more gradual), and normovolemic or hypervolemic. Ouring hemodilution the hemoglobin level is reduced, resulting in fewer erythrocytes being lost per amount of blood loss, but also in a decrease in oxygen carrying capacity. This reduction in oxygen carrying capacity can be compensated tor by a number of mechanisms. These include an increase in cardiac output, a redistribution of the cardiac output, an increase in oxygen extraction ratio and a shift in the oxygen dissociation curve to the right. With respect to hemodilution techniques and the amount of blood that can be saved by these techniques, the issue of the lower safe limit of the hematocrit perioperatively remains a matter of debate.

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