[Effects of hemodilution on cerebral arterial blood flow velocity and cerebrovascular CO2 reactivity]

We investigated the effects of normovolemic hemodilution on the mean blood flow velocity of the middle cerebral artery (Vm) and the cerebrovascular CO2 reactivity (K-value) by transcranial doppler sonography in ten patients undergoing elective surgeries. Vm during hemodilution (Hct of 24%) significantly increased for 8% in normocarbia (PaCO2 of 40 mmHg) and for 15% in hypocarbia (PaCO2 of 30 mmHg), compared with that in prehemodilution (Hct of 33%), at the range of mean blood pressure < or = 90 mmHg. However, in hypercarbia (PaCO2 of 50 mmHg), there were no significant differences in Vm between during hemodilution and in pre-hemodilution. K-values during hemodilution were significantly lower than those in pre-hemodilution at the same hypotensive range. These findings suggest that moderate hemodilution may elicit the compensatory increase of cerebral blood flow by cerebrovascular dilation and therefore induce no disturbance for normal cerebral hemodynamics.