Increased arterial oxygen content by artificial haemoglobin induces a decrease in regional cerebral blood flow and decreased regional cerebral oxygen delivery.
OBJECTIVE
Under physiological conditions, cerebral oxygen delivery is kept constant by adaptation of the regional cerebral blood flow (CBF) in relation to the oxygen content. So far, decreases of the regional CBF induced by a higher arterial oxygen content have been produced under hyperbaric or hyperviscous conditions. We tested whether local CBF is also reduced by a high haemoglobin (Hb) concentration at a normal haematocrit (Hct).


METHODS
Compared with controls (n=8), Hb content was increased to 19 g dl(-1) in conscious rats by isovolaemic replacement of the plasma fraction with an artificially high Hb solution (Hb-based oxygen carriers; HH group, n=8). In another group (n=8), Hct was decreased by isovolaemic exchange with an Hb-based oxygen carrier resulting in a normal Hb content (NH group). Mean and regional CBF was measured by iodo-[(14)C]-antipyrine autoradiography. Oxygen delivery was calculated from arterial oxygen content and CBF.


RESULTS
Compared with the controls (Hb 15.3 g dl(-1), Hct 0.44), mean CBF was lower in the HH (Hb 20.3 g dl(-1), Hct 0.44) group by 23% (P < or = 0.05), but remained unchanged in the NH group (Hb 15.0 g dl(-1), Hct 0.29). On a local level, hyperoxygenation reduced CBF in 22 out of 39 brain regions. In the NH group mean CBF was unchanged, whereas local CBF was higher in 10 areas. In both groups, overall cerebral oxygen delivery was unchanged compared with the control group. Locally though, high arterial Hb content decreased oxygen delivery in one-third of the brain structures.


CONCLUSIONS
Whereas the overall cerebral oxygen delivery in the brain is maintained during hyperoxygenation and haemodilution, local oxygen delivery is decreased by high arterial Hb content in some brain regions.
Schöler
Michael
M
Clinic for Anesthesiology and Critical Care Medicine, Medical Faculty Mannheim, Germany.
Lenz
Christian
C
Kuschinsky
Wolfgang
W
Waschke
Klaus F
KF
Knels
Ralf
R
Frietsch
Thomas
T
D000818:Animals; D001158:Arteries / Q000378:metabolism; D001921:Brain / Q000098:blood supply* / Q000378:metabolism*; D002560:Cerebrovascular Circulation; D006454:Hemoglobins / Q000378:metabolism*; D008297:Male; D010100:Oxygen / Q000097:blood*; D051381:Rats; D017207:Rats, Sprague-Dawley
D006454:Hemoglobins; D010100:Oxygen