New mathematical model for the correct prediction of the exchangeable blood volume during acute normovolemic hemodilution

Abstract

Exchangeable blood volume is predicted more accurately by the new iterative model than by the Bourke and Smith formula. The iterative model leads to an improvement in patient safety and provides a physiologically adequate basis for future studies investigating the efficacy of ANH in reducing allogenic blood transfusions.

Effects of standardized acute normovolemic hemodilution on intraoperative allogeneic blood transfusion in patients undergoing major maxillofacial surgery

“…The recalculation revealed that the BL fract of 50%, postulated in the mathematical model as the lower limit for ANH to become efficacious 26 , corresponded to a BL fract of 26% in our scenario. This value should be further adjusted downwards since the mathematical formula applied in the theoretical study 2 overestimates the exchangeable BV necessary to meet a predefined post-ANH target Hb 14 . In addition to this difference, in the clinical scenario the decision to transfuse is more often based on the individual clinical experience and interpretation of physiologic parameters rather than on a predefined transfusion protocol 4 .…”

“…However, it is difficult to transfer the results of these theoretical considerations into the clinical practice. For example, targeting a low post-ANH Hb may often be impossible in elderly patients suffering from cardiovascular and/or pulmonary diseases or in healthy young patients it may become a timeconsuming process, because the exchangeable blood volume necessary to meet a predefined post-ANH target Hb will be high and difficult to predict due to the lack of reliable mathematical formula 14 . As a consequence, intermediate control-measurements of Hb may become necessary and delay the start of the operation.…”

Risk Factors Influencing Transfusion Rates in DIEP Flap Breast Reconstruction

“…The authors believe Meier et al's iterative method for calculating blood loss is the most accurate method. 37 Estimated blood loss is a subjective visual estimation of surgical blood loss from suction and sponges. Furthermore, the intraoperative estimated blood loss was unreliably entered into the patient charts in our study.…”

“…31,[35][36][37] We used a third blood loss calculation described by Meier et al that was found to more accurately calculate the exchangeable blood volume required for acute normovolemic hemodilution. 37 If red blood cells are distributed homogeneously within the vasculature (hb1) after one hemodilution step (hb2), then the equation reads: hb2 ϭ [hb1 ϫ (blood volume Ϫ E)]/(blood volume), where E is considered the volume replaced in one hemodilution step and hb1 and hb2 are the original and final hemoglobin values, respectively. Blood volume is calculated using the formula 0.414 ϫ T 3 ϩ 0.0328 ϫ BW -0.03, where T is height in meters and BW is weight in kilograms.…”

Acute Normovolemic Hemodilution in Cardiac Surgery

“…72 Recently, a new mathematical model has been developed that seems to predict more accurately the exchangeable blood volume. 73 This algorithm, which can be obtained from the authors, could enhance patient safety and provide a correct physiological basis for further studies addressing the efficacy of ANH.…”