The aim of blood transfusion is to provide sufficient oxygen for the whole body, and to maintain the balance of oxygen supply and oxygen consumption. Factors associated with oxygen supply are hemoglobin level, cardiac output (CO), and oxygen saturation. Oxygen consumption is increased by the increase of metabolism, which could be reflected by increase of heart rate, blood pressure, and body temperature. If a patient's oxygen supply is decreased or oxygen consumption is increased, he will need a higher hemoglobin level to maintain the balance. Based on these findings, the investigators hypothesize that index of transfusion trigger for patients with hemoglobin level between 7/dL and 10g/dL could be calculated by their CO (reflectd by the use of adrenalin), and routine monitoring parameters including pulse oximetry and core temperature.