Effects of normovolaemic haemodilution on middle cerebral artery blood flow velocity and oxygen delivery.
OBJECTIVE
Assessment of the effects of normovolaemic haemodilution on middle cerebral artery blood flow velocity with transcranial Doppler ultrasonography, intracranial pressure, cerebral perfusion pressure, arterial oxygen content and cerebral oxygen delivery.


METHODS
Normovolaemic haemodilution was induced in rabbits under general anaesthesia, and the haematocrit was allowed to decrease to 30% in Group 1 (n = 6) and to 20% in Group 2 (n = 6). Peak systolic and diastolic velocities, mean blood flow velocity, and pulsatility and resistance indices of the middle cerebral artery were measured by transcranial Doppler ultrasonography. Changes in intracranial pressure, cerebral perfusion pressure, arterial oxygen content and cerebral oxygen delivery were also assessed.


RESULTS
In Group 2, middle cerebral artery blood flow velocity increased from 0.4 +/- 0.01 to 0.51 +/- 0.02 m s(-1) after the induction of normovolaemic haemodilution (P = 0.04), while arterial oxygen content decreased from 16.2 +/- 0.1 to 8.5 +/- 0.1 mLdL(-1) (P = 0.002). The decrease in cerebral oxygen delivery from 6.5 +/- 0.2 to 4.3 +/- 0.2 was also significant (P = 0.02). However, no associated changes in intracranial pressure and cerebral perfusion pressure could be demonstrated.


CONCLUSIONS
Normovolaemic haemodilution resulted in an increase in the mean blood flow velocity of the middle cerebral artery. However, this increase did not compensate for the consequences of the altered oxygen delivery to the brain when the haematocrit was reduced to 20%.
Karadibak
K
K
Dokuz Eylül University School of Medicine, Department of Anesthesiology, Izmir, Turkey.
Gökmen
N
N
Erbayraktar
S
S
Göktay
Y
Y
Taplu
A
A
Arkan
A
A
Erkan
N
N
D000818:Animals; D001783:Blood Flow Velocity / Q000502:physiology*; D002560:Cerebrovascular Circulation / Q000502:physiology*; D006438:Hemodilution; D020768:Middle Cerebral Artery / Q000000981:diagnostic imaging / Q000502:physiology*; D010100:Oxygen / Q000097:blood*; D011817:Rabbits; D017585:Ultrasonography, Doppler, Transcranial
D010100:Oxygen