Systemic and renal hemodynamics after moderate hemodilution with HbOCs in anesthetized rabbits

Hb-based O-2-carrying solutions (HbOCs) have been developed as red blood ce ll substitutes for use in patients undergoing hemodilution. Variously modif ied Hb with diverse solution properties have been shown to produce variable hemodynamic responses. We examined, through pulsed-Doppler velocimetry, th e systemic and renal hemodynamic effects of dextran-benzene-tetracarboxylat e-conjugated (Hb-Dex-BTC), bis(3,5-dibromosalicyl) fumarate cross-linked (a lpha alpha-Hb), and o-raffinose-polymerized (o-raffinose-Hb) Hb perfused in rabbits after moderate hemodilution (30% hematocrit), and we compared the effects of these Hb solutions with the effects elicited by plasma volume ex panders. In addition, vascular hindrance (resistance/blood viscosity at 128 .5 s(-1)) was calculated to determine whether a moderate decrease in the vi scosity of blood mixed with HbOCs may impair vasoconstriction as a result o f autoregulation after infusion of cell-free Hb. No changes were observed i n renal hemodynamics after hemodilution with reference or Hb solutions. Inc rease in blood pressure and vascular resistance was found with Hb-Dex-BTC a nd alpha alpha-Hb (for 180 min) and, to a lesser extent, with o-raffinose- Hb (for 120 min). Furthermore, Hb-Dex-BTC (high viscosity) and o-raffinose- Hb (medium viscosity) induced comparable increases in vascular hindrance ( from 0.091 to 0.159 and from 0.092 to 0.162 cm(-1), respectively) but far l ess than that produced by alpha alpha-Hb (low viscosity, from 0.092 to 0.20 0 cm(-1)). These results suggest that maintaining the viscosity of blood by infusing solutions with high viscosity makes it possible to limit vasocons triction due to autoregulation mechanisms and mainly caused by hemodilution per se.