The effect of hemodilution on cerebral blood flow velocity in anesthetized patients

Transcranial Doppler is used to estimate changes in cerebral blood flow, but the effect of hemodilution on cerebral blood flow velocity (CBFV) in anesthetized patients has not been evaluate d. The aim of this study was to measure the effect of isovolemic hemodilution on CBFV and lumbar cerebrospinal fluid pressure (P-CSF) in anesthetized patients without change in other physiological variables that may affect CBFV. Patients undergoing hemodilution were compared with a control group undergoing no hemodilution. With hemodilution, hematocrit decreased from 38% +/- 3% to 30% +/- 2%, arterial oxygen content (Cao(2)) decreased from 17.5 +/- 1.3 to 13.9 +/- 0.9 mL/dL, and CBTV increased from 50 +/- 10 to 58 +/- 10 cm/s. An equivalent of cerebral arterial O-2 transport calculated as Cao(2) x CBFV did not significantly change. Over the same time interval, there were no changes in the control group. There was no statistically significant change in P-CFS pulsatility index, Paco(2), blood pressure, heart rate, or body temperature in either group. Mie conclude that CBFV reflects cerebral blood Row changes after hemodilution. Implications: Hemodilution increases cerebral blood flow but mag; change the cerebral artery diameter, which could confound perioperative measurement of cerebral blood flow velocity. This study found transcranial Doppler ultrasonography to accurately assess the effects of hemodilution on the cerebral circulation, but the hematocrit should be taken into account to fully understand perioperative cerebral blood Row velocity changes.