Based on the aim of blood transfusion that maintain the balance of oxygen supply and oxygen consumption, the investigators hypothesize that index of transfusion trigger for patients with hemoglobin level between 6g/dL and 10g/dL could be calculated by parameters including infusion rate of inotropic drugs for maintaining normal cardiac output, fraction of inspired oxygen, core temperature, and torlerance to anemia. To verify this hypothesis, the investigators present West China Transfusion Score for Critically-ill Patients(WCTS-CP) for the trigger of transfusion according to the patient's history and monitoring parameters, and the investigators design a randomized controlled clinical trial to test this score.