Development and validation of a mathematical algorithm for quantifying preoperative blood volume by means of the decrease in hematocrit resulting from acute normovolemic hemodilution

BACKGROUND: The interindividual variability of blood volume (BV) is high. The aim of this work was to use the decrease in large-vessel hematocrit (HKLV) during acute normovolemic hemodilution (ANH) as an instrument for estimating preoperative BV. STUDY DESIGN AND METHODS: In 39 patients, (Group 1) preoperative ANH was performed. Plasma volume, red cell volume, and HKLV were measured before and 30 minutes after ANH, respectively. In a retrospective analysis, a mathematical algorithm was developed for estimating BV before ANH by means of the measured changes in HKLV and the amount of blood removed during ANH. To validate the method prospectively, ANH was performed in an additional 10 patients (Group 2). Preoperative BV was estimated and measured in the same way as in Group 1. RESULTS: In Group 1, the mean difference between estimated and measured BV before ANH was 200 +/- 403 mL (5.14 +/- 10.12%; p > 0.05; r = 0.8). In Group 2, the estimated BV before ANH was 41 +/- 348 mL (-0.53 +/- 7.84%) lower than the measured BV (p > 0.05; r = 0.94). In this group, however, two patients with an extraordinarily small (2691 mL) and large (6172 mL) preoperative BV, respectively, were identified correctly by means of the algorithm. CONCLUSIONS: The changes in HKLV determined during ANH provide a good "bedside" estimation of preoperative BV.