Mathematical considerations in the practice of acute normovolemic hemodilution

Abstract

ANH involving the removal of 2 to 3 units (450 mL each) may be useful in patients with anticipated blood loss exceeding 50 percent of estimated blood volume, high initial hematocrit, and a capacity to tolerate dilution-induced anemia.

Blood Transfusion Practices in Major Orthopaedic Surgery

“…Mathematical models indicate that ANH is only suitable for a minority of patients (Kick 1997). These include healthy adults in whom a relatively low target haemoglobin, both intraoperatively and postoperatively is acceptable, with an anticipated blood loss of greater than 50% and a relatively high starting haemoglobin ).…”

“…These include healthy adults in whom a relatively low target haemoglobin, both intraoperatively and postoperatively is acceptable, with an anticipated blood loss of greater than 50% and a relatively high starting haemoglobin ). The maximum volume of blood that can be withdrawn depends on the preoperative haemoglobin, the lowest acceptable intraoperative haemoglobin level and the estimated blood loss (Brecher 1997;Cohen 1995;Kick 1997). …”

10 Autologous Hemotherapy

“…Preoperative normovolemic hemodilution can be considered for patients with preoperative hematocrit/hemoglobin concentrations at the upper limit of normal and for whom an intraoperative blood loss is anticipated of >50% of the blood volume, and who are able to tolerate hemodilution-derived anemia due to their general clinical state [27,43]. Within the framework of any risk-benefit analysis, the physician should also bear in mind that the maximum possible saving (which is only achievable when preoperative hemoglobin concentrations are at the upper limit of normal) does not exceed 1-1.5 homologous RBC concentrates [7,39].…”

Acute Normovolemic Hemodilution in Cardiac Surgery

“…6 Several authors have developed equations to calculate the efficacy of ANH as a function of surgical blood loss, initial hematocrit, target post-ANH hematocrit, and hematocrit used as the transfusion trigger. [52][53][54] Presuming a "usual" surgical patient (preoperative hematocrit of 32-36%) and a transfusion decision based exclusively on a trigger hemoglobin of 6-7 g/dL, Weiskopf 55 calculated a minimal fractional blood loss of 50% to enable any saving of allogeneic red blood cells with ANH. Expressed as a fraction of the patient' s blood volume, 55% to 77% of total blood volume must be lost during surgery in order to achieve savings of 180 mL of RBCs, representing one standard unit.…”