Acute normovolemic hemodilution: physiology, limitations, and clinical use

Abstract

The amount of red blood cells and other plasma constituents lost during surgical bleeding is reduced by preoperative dilution of the circulating blood volume. ANH is traditionally performed immediately before surgery, either before or shortly after anesthesia induction. Conceptually, it is crucial to do ANH before the major surgical bleeding phase. Therefore, it is also conceivable to perform ANH intraoperatively during an initial, nonhemorrhagic phase. The blood withdrawn is simultaneously replaced with an appropriate volume of crystalloid or colloid fluids (alone or in combination) to maintain normovolemia.5,6 Maintaining perioperative normovolemia is crucial because recent studies have shown that an optimal filling of the heart improves cardiac function, decreases postoperative morbidity, and shortens hospital stay.7-9 The target hematocrit with ANH is variable but is often around 25% to 30%. More extreme hemodilution (eg, 20%) is likely to be more efficacious with regards to blood conservation, but the risks are greater, particularly for patients with preexisting medical conditions such as coronary heart disease.5 In addition, it requires larger quantities of blood to be withdrawn rendering it time consuming (10-15 minutes per bag of 450 mL) and increasing the risk of compromising coagulation by the infusion of large quantities of colloids.10-12