Predictors of transfusion risk in elective knee surgery.

Two hundred seventy-nine patients undergoing primary unilateral total knee replacement and 280 patients undergoing primary bilateral total knee replacements were reviewed retrospectively. Patients' height, weight, hemoglobin level before donation, hemoglobin level before surgery, autologous donation, number and type of transfusions whether autologous or allogeneic, and hemoglobin at discharge were collected from hospital and clinic records. The average drop in hemoglobin was 3.85 g/dL in the group of patients undergoing unilateral total knee replacement and 5.42 g/dL in the group of patients undergoing bilateral total knee replacements. The preoperative hemoglobin and blood volume seemed to be very strong, statistically significant predictors of transfusion risk in single and bilateral knee replacements. In unilateral total knee replacement, patients with a hemoglobin of greater than 13 g/dL had only an 8% chance of transfusion and if they donated autologous blood, 66% of the blood was wasted. Preoperative anemia was a strong predictor of transfusion risk in patients undergoing unilateral and bilateral total knee replacements and carried a very high allogeneic transfusion exposure risk, even in patients who had donated blood preoperatively. A nomogram was developed using blood volume and predonation hemoglobin to predict transfusion risk and need to predeposit autologous blood in patients undergoing unilateral and bilateral total knee replacements.