Yk. Tu et al., CEREBRAL OXYGEN-TRANSPORT AND METABOLISM DURING GRADED ISOVOLEMIC HEMODILUTION IN EXPERIMENTAL GLOBAL-ISCHEMIA, Journal of the neurological sciences, 150(2), 1997, pp. 115-122
To verify the optimal hematocrit (Hct) level in the treatment of cereb
ral ischemia, cerebral oxygen transport (CTO2) and cerebral oxygen met
abolism (CMRO2) in graded isovolemic hemodilution were evaluated durin
g cerebral ischemia. Isovolemic hemodilution with low molecular weight
dextran to stepwise lower Hct from 43% to 36%, 31%, and 26% was carri
ed out in 13 splenectomized dogs, 6 h after global cerebral ischemia.
Global ischemia of the animals was produced by multiple intra- and ext
racranial ligations of cerebral arteries. Cerebral blood flow (CBF) wa
s measured with radioisotope labeled microspheres. CTO2, CMRO2, and ox
ygen extraction fraction (OEF) were calculated from CBF, arterial oxyg
en content (CaO2), and venous oxygen content (CvO(2)). In dogs with gl
obal cerebral ischemia, CBF increased with graded isovolemic hemodilut
ion (r=-0.73, P<0.05). CTO2 reached its highest value at a Hct level o
f 31.3%. CTO2 at Hct of 36.1% and 31.3% was statistically different fr
om the value measured at a Hct of 43.3%, and there was a decrease when
Hct was lowered to 25.9%. CMRO2 was the highest when Hct was at 31.3%
and differed significantly from the value measured at a Hct of 43.3%.
There was a 10% increase of OEF when Hct was at 25.9%; however this c
hange was not statistically significant compared with the OEF at Hct o
f 36.1% and 31.3%: respectively. These findings indicate that CTO2 and
CMRO2 were the highest when Hct was reduced to 31% in hemodilution. H
ct at 31% is the optimum for cerebral metabolism in ischemic status. U
ncoupling of CTO2, CMRO2 with CaO2 was also observed in this study. Th
is phenomenon suggests that hemodilution to augment cerebral circulati
on may be at least partially attributed to the beneficial effects of h
emorheologic improvement in the microcirculation of the ischemic brain
. (C) 1997 Elsevier Science B.V.