Does Acute Normovolemic Hemodilution Decrease Transfusion Requirements during Cardiac Surgery? Hohn et al. (page 276)
Using strict transfusion criteria, Hohn et al. conducted a prospective randomized trial to test the efficacy of acute normovolemic hemodilution (ANH) during cardiac surgery. Eighty adult patients scheduled for elective cardiac surgery with use of moderate hypothermic cardiopulmonary bypass (CPB) were enrolled in the study. Patients in the control group underwent cardiac surgery with the customary blood-saving techniques used at the investigators’ institution: filling of the extracorporeal circuit with saline isotonic fluid; intraoperative blood salvage; reinfusion of shed mediastinal blood; administration of intravenous aprotinin; and external heating at the end of CPB. In the treatment group, ANH was added to the above procedures.
Complete white blood cell counts, coagulation profiles, serum creatinine, and hepatic enzyme levels were obtained the day before surgery. Hematocrit, thrombocyte count, prothrombin time, and partial thromboplastin time were repeated the day of surgery (just before CPB), after surgery, postoperatively on days 1, 2, 5, and at discharge. Intraoperative monitoring included continuous blood pressure, oxygen saturation, and transesophageal echocardiography. The investigators used the same transfusion criteria in both control and treatment groups: before CPB if hematocrit (Hct) was <28%, during CPB if Hct was <17%, and after CPB if Hct was <25%. When needed, both patient groups received first autologous blood salvaged intraoperatively. Acute normovolemic hemodilution patients then received their blood removed by ANH and, if necessary, additional allogeneic packed red cells.
The amount of whole blood collected during ANH ranged from 10–40% of the patients’ estimated blood volume. Intraoperative and postoperative blood losses did not differ between control and ANH groups. Allogeneic blood was given to 29% of control group patients and to 33% of ANH group patients. Platelet count, prothrombin time, and partial thromboplastin time were similar in both groups, both intraoperatively and postoperatively. At discharge, control group and ANH group patients also had similar Hct values. The authors concede that the transfusion trigger chosen for their study probably contributed to a lower transfusion rate in both groups of patients. In addition, the ANH group patients received more diuretics than did patients in the control group. These and other factors may explain why there was no benefit demonstrated for adding ANH to the existent CPB regimen of intravenous aprotinin, intraoperative cell saving, and external heating. It may be that ANH would be more effective in patients excluded from this study, i.e., those with combined coronary and valvular surgery, emergency surgery, or those with known coagulopathy risk.