Intravascular volume expansion is prominently overestimated via hemoglobin concentration: a placebo-controlled and cross-over trial.

Blood volume (BV) expansion by means of intravenous infusion of colloids is an established procedure in clinical interventions. The essential questions of how much of the infused fluid stays in the circulation according to measured changes in hemoconcentration are uncertain. A placebo-controlled, single-blinded, and cross-over design was implemented to assess the effect of a definite increment in BV on hemodilution, as determined by hemoglobin concentration ([Hb]). Healthy women (n = 17) and men (n = 19) matched by sex, age (age = 26 ± 4 vs. 27 ± 3 yr, P = 0.522), and physical activity were subjected in a blind manner to the intravenous infusion of placebo-sham (PBO-sham) via saline infusion (10 mL; BD 0.9% NaCl) or albumin (volume equivalent to 10% of BV; Albumin CSL 20%). [Hb] was slightly reduced (-2.4%) after the PBO-sham infusion. For the albumin infusion, the amount of fluid infused ranged from 325 to 810 mL (547 ± 112 mL) in order to elicit a 10% increment in BV in each individual. [Hb] was markedly reduced (-17.2%) (13.8 ± 1.6 vs. 11.5 ± 1.4 g·dL^-1, P < 0.001) after albumin infusion. The magnitude of hemodilution was well above the expected decrement (-9%) in all individuals. Sex differences were not detected. Cardiac chamber volumes were expanded by 7-10% by albumin infusion, without changes in LV filling pressure (P = 0.582). In conclusion, a colloid infusion eliciting a 10% BV expansion is markedly overestimated according to changes in [Hb] in healthy women and men. The overestimation of BV expansion ranges from 35 to 135% irrespective of sex.