What factors should we consider in deciding when to transfuse patients undergoing elective cardiac surgery?

Blood transfusion remains one of the commonest interventions carried out upon individuals undergoing cardiac surgery. Despite this, the scientific rationale on which to base this decision is limited. Currently, hemoglobin concentration is often used as the sole guide as to when a transfusion may be required. A fall in hemoglobin concentration is often assumed to be associated with a similar drop in red cell volume. A review was undertaken of all the relevant peer-reviewed literature to determine what factors we should consider when deciding to transfuse elective cardiac surgery patients. The large fluid load associated with cardiac surgery, primarily from the cardiopulmonary bypass circuit, may have a significant dilutional effect. In such a scenario, several interlinked protective mechanisms may ensure that tissue oxygenation is maintained, including a reduction in blood viscosity, a decrease in systemic afterload, and an increase in cardiac output. Furthermore, oxygen requirements during the initial perioperative phase are reduced because of the effect of general anesthesia and hypothermia during cardiopulmonary bypass. When deciding to transfuse, consideration should be given to red cell volume, circulatory status, and oxygen requirement. It is possible that such an all-encompassing approach would reduce the incidence of unnecessary, and potentially counterproductive, red cell transfusion in cardiac surgery.