Perfusion changes in hemodilution. The effect of extensive isovolemic hemodilution with gelatin and hydroxyethylstarch solutions on cerebral blood flow velocity and cutaneous microcirculation in humans

OBJECTIVE: Quantifying the influence of extreme isovolemic hemodilution (NH) with different colloids on cerebral blood flow velocities (transcranial Doppler sonography) and cutaneous microcirculatory blood flow (laser Doppler flowmetry) in healthy, non-premedicated volunteers was the aim of this study. METHODS: In seven volunteers (randomized cross-over design) 20 ml/kg blood was withdrawn within 30 min and simultaneously replaced with 6% hydroxyethyl starch (200,000/0.5, HES) or 3% gelatin (GEL). Thirty minutes later, the autologous blood was retransfused (RT) within 30 min. Due to a severe allergic reaction to gelatin in one volunteer, only 6 GEL-NH were evaluated. Recorded parameters were: mean blood flow velocities (Vm-MCA) as well as the pulsatility index (PI) and the resistance index (RI) over the middle cerebral artery. In addition laser Doppler flux (FLUX), cell velocity (SPEED), mean arterial pressure (MAP), heart rate (HR), hemoglobin (Hb) and hematocrit (Hc) were monitored. RESULTS: NH resulted in a withdrawal volume of 1498 +/- 85 ml (HES) and 1493 +/- 95 ml (GEL), (mean +/- SD) and induced a decrease in hemoglobin from 40.9 to 29.0% (HES) and from 39.8 to 30.0% (GEL). RT increased Hc to 34.2% (HES) and 34.5% (GEL). MAP and HR showed no significant alterations in both groups. Following NH, Vm-MCA rose almost the same way in either case (26% HES), 21% (GEL), but decreased continuously again during RT. After completing RT, only in the HES group Vm-MCA still remained higher than baseline values (14% HES, only 3% GEL). Similar inverse regression lines were found for the two groups between Hc and Vm-MCA: Vm-MCAHES (cm/s) = -1.27 x Hc + 110.9; r = 0.98, P < 0.001 and Vm-MCAGEL (cm/s) = -1.32 x Hc + 110.9; r = 0.91, P < 0.001]. Furthermore, as a result of NH, FLUX and SPEED increased about 61% and 38% in the HES group and remained on higher values in comparison with starting positions (21% FLUX, 13% SPEED). However, the results in the GEL group were of a different kind: FLUX and SPEED increased stupendously to 291% and 114% combined with NH, but both were reduced by RT on a large scale (39 and 27% below baseline values). Whereas RI showed no group differences, there was a remarkable drop in PI during RT (17% HES, 12% GEL). CONCLUSION: The two plasma expanders studied show a close inverse correlation between the alterations of blood flow velocities in the middle cerebral artery and systemic hemoglobin and hematocrit values. In both groups the change in blood flow velocities is comparable. For the first time the results of relative changes in blood flow velocities following hemodilution and retransfusion in healthy volunteers are described that correspond closely by relative cerebral blood flow alterations found in animal studies as well. Moreover, a non-linear correlation of cutaneous microcirculation was shown by means of HES, but also by GEL. Obviously, there was the GEL group to be responsible for pronounced differences in cutaneous circulation.