Extreme hemodilution in rabbits: An in vitro and in vivo thrombelastographic (R) analysis

Isovolemic hemodilution is used to decrease the incidence of blood transfus ions. However, the effects of the degree of hemodilution and the fluid used on hemostasis are controversial. We tested the hypothesis that hemodilutio n and the fluid administered would adversely alter Thrombelastographic(R) ( Haemoscope, Skokie, IL) variables (reaction time, alpha angle and maximal a mplitude). Conscious rabbits had blood sampled from ear arteries and dilute d 0% or 75% in viiro with one of four solutions: 6% hetastarch in 0.9% NaCl , 5% human albumin in 0.9% NaCl, or balanced electrolyte solutions containi ng either 6% pentastarch or 6% hetastarch. Isoflurane-anesthetized rabbits were randomly assigned to groups (n = 9 per group) that underwent in vivo i sovolemic hemodilution (75% of estimated blood volume removed), with blood replaced with one of the four solutions mentioned previously. In vitro hemo dilution resulted in a significant (P < 0.05) decrease in hemostatic functi on (increase in reaction time, decrease in a angle and maximal amplitude) t hat was largest after hemodilution with albumin. However, although in vivo hemodilution significantly (P < 0.05) decreased reaction time, increased th e a angle, and decreased maximal amplitude, there were no significant fluid -dependent effects. Implications: The effects of hemodilution and the fluid used on Thrombelastographic(R) (Haemoscope, Skokie, IL) variables are mark edly different between in vitro and in vivo hemodilution studies.