Hypervolemic hemodilution: An alternative to acute normovolemic hemodilution? A mathematical analysis

Background. Hypervolemic hemodilution has been proposed as an alternative t o normovolemic hemodilution to reduce homologous blood transfusions. So far , convincing data supporting this concept are unknown. Materials and methods. We therefore present a mathematical model calculatin g the efficacy of hypervolemic, normovolemic, and "no" hemodilution. Hyperv olemic hemodilution constituted volume expansion (20% of estimated blood vo lume) maintained throughout surgery. Normovolemic hemodilution contained is ovolemic exchange of blood (40% of estimated blood volume) vs colloid as we ll as retransfusing blood plus colloid to maintain minimal acceptable hemat ocrit, e.g., transfusion trigger. To determine the efficacy of each techniq ue maximal allowable blood loss and final postoperative hematocrit were cal culated, Maximal allowable blood loss referred to the amount of blood lost during surgery after which homologous blood transfusion became necessary. Results. Recalculating published clinical data strongly validated the formu las used for our model. Hypervolemic hemodilution always revealed lowest ma ximal allowable blood losses. Normovolemic hemodilution constantly ensured highest maximal allowable blood losses, For blood losses <40% of blood volu me, hypervolemic and normovolemic hemodilution provided almost identical fi nal postoperative hematocrits. But in contrast to normovolemic hemodilution , hypervolemic hemodilution did not carry the risk of severe transient, ret ransfusion-induced hypervolemia. "No" hemodilution always gave lowest final postoperative hematocrits. Conclusions, Thus, hypervolemic hemodilution cannot replace normovolemic he modilution to reduce homologous transfusions, but for blood losses <40% of blood volume hypervolemic hemodilution appears to be superior. (C) 1999 Aca demic Press.