Extreme hemodilution in rabbits: An in vitro and in vivo Thrombelastographic® analysis

Isovolemic hemodilution is used to decrease the incidence of blood transfusions. However, the effects of the degree of hemodilution and the fluid used on hemostasis are controversial. We tested the hypothesis that hemodilution and the fluid administered would adversely alter Thrombelastographic® (Haemoscope, Skokie, IL) variables (reaction time, α angle and maximal amplitude). Conscious rabbits had blood sampled from ear arteries and diluted 0% or 75% in vitro with one of four solutions: 6% hetastarch in 0.9% NaCl, 5% human albumin in 0.9% NaCl, or balanced electrolyte solutions containing either 6% pentastarch or 6% hetastarch. Isoflurane-anesthetized rabbits were randomly assigned to groups (n = 9 per group) that underwent in vivo isovolemic hemodilution (75% of estimated blood volume removed), with blood replaced with one of the four solutions mentioned previously. In vitro hemodilution resulted in a significant (P < 0.05) decrease in hemostatic function (increase in reaction time, decrease in α angle and maximal amplitude) that was largest after hemodilution with albumin. However, although in vivo hemodilution significantly (P < 0.05) decreased reaction time, increased the α angle, and decreased maximal amplitude, there were no significant fluid-dependent effects. Implications: The effects of hemodilution and the fluid used on Thrombelastographic® (Haemoscope, Skokie, IL) variables are markedly different between in vitro and in vivo hemodilution studies.