Cerebral blood flow velocity during isovolemic hemodilution and subsequentautologous blood retransfusion

Purpose: To quantify the influence of hematocrit on cerebral blood flow vel ocity (CBFV) in healthy volunteers undergoing acute isovolemic hemodilution (HD) with hydroxyethyl starch 10% (HES) and subsequent autologous whole bl ood retransfusion (RT). Methods: In 11 volunteers 20 ml . kg(-1) blood was withdrawn over 30 min an d simultaneously replaced with HES 10%. Thirty min later, RT was-started at a constant rate over 30 min. Recorded parameters included: CBFV, pulsatili ty-index (PI) and resistance-index (RI) of the middle cerebral artery(MCA). Blood pressure (BP), heart rate (HR), hemoglobin (Hb), hematocrit (Hc) per ipheral O-2-saturation (SpO(2)), PETCO2, arterial oxygen content (CaO2) and cerebral arterial O-2-transport (C-E-DO2 = CaO2 x Vm-MCA) were monitored. Results: An average of 1570 total blood was withdrawn which resulted in a d ecrease in Hb from 14.5 mg . dl(-1) to 10.3 mg . dl(-1); Hc (and CaO2) decr eased from 41.8% (19.8 ml . dl(-1)) to 29.6% (14.2 ml . dl(-1); P < 0.01). Vm-MCA increased from 61.2 cm . sec(-1) to 77.3 cm . sec(-1) (P < 0.01). Fo llowing RT;Vm-MCA decreased again, but remained higher than baseline (P < 0 .01). PI decreased by 13% following RT(P < 0.05). There were no changes in RI, HR, BP, SpO(2) and PETCO2. Regression lines could be fitted between He and Vm-MCA, Vm-MCA and CaO2, and between He and CEDO2. Conclusions: Transcranial Doppler changes in blood flow velocities correlat ed with the simultaneously recorded systemic Hc and CaO2 values. We found a 2% increase in CBN for each 1% decrease in Hc and CaO2.