Transfusion in Cardiac Valve Surgery

Patients are randomly assigned to restrictive-threshold group and liberal-threshold group before cardiac group. Patients are included in this research when their Hct meets 24% during CPB. Arterial blood gas analysis will be done in 0.5h, 1.5h, 2.5h, 3.5h...after CPB start and 0.5h before CPB finish. Arterial blood gas analysis will be done every 4h in intensive care unit(ICU) and everyday in general ward. Restrictive-threshold group: The transfusion threshold is Hemoglobin(Hb) ≤ 6.0g/dL or Hct ≤ 18% during CPB; postoperative Hb ≤ 7.0g/dL or Hct ≤ 21% in ICU or general ward. Liberal-threshold group: The transfusion threshold is Hb ≤ 8.0g/dL or Hct ≤ 24% during CPB; postoperative Hb ≤ 10.0g/dL or Hct ≤ 30% in ICU or general ward. If the Hb or Hct fall below the threshold at any time, 2 unit of blood cells is administered as soon as possible. Test Hb or Hct again, if is under the threshold 2 unit blood cells will be given until reach the threshold.