Introduction: Anemia is to reduce the capacity of oxygen transport by blood. Capacity of oxygen transport is one of the functions of red blood cells, circulatory in blood volume, therefore it can be said that anemia is reduction of red blood cells volume. The problem of this clinical definition is the effect of plasma volume on hematocrit and hemoglobin concentration.Goal: To determine systemic oxygenation criteria.Methods: Study and research on internet and review of literature.Problem Statement: On the condition that intravascular volume is maintained anemia is well tolerated, if blood volume is normal, redaction of hemoglobin to 3gr/dl causes tissue oxygenation disorder. This means that cardiac output is more important than blood hemoglobin levels in order to maintain tissue oxygenation. Superiority to cardiac output becomes more obvious when nature of hypovolemic shock and carcinogenic shock become specified while there is not anemia shock at all. Because shock is accompanied with the decline of tissue oxygenation. So, until anemia reach to dangerous levels it cannot be known as the reason of shock because in mild levels anemia doesn't cause tissue oxygenation disorder. A better criterion for evaluating systemic oxygenation is extraction of peripheral oxygen measured as sao2-svo2 differences.Conclusion: By accepting this reality, therefore most RBC transfusions to correct anemia status will not improve tissue oxygenation also concentration of hemoglobin is not a valuable criterion in order to evaluate the need for transfusion. A better criterion for evaluating systemic oxygenation is extraction of peripheral oxygen, measured as sao2-svo2 differences.