The present study was designed to evaluate the effects of clonidine on huma
n middle cerebral artery flow velocity and the cerebrovascular CO2 response
during sevoflurane anesthesia using transcranial Doppler ultrasonography.
he subjects were nine awake volunteers (group A) and 18 patients receiving
oral preanesthetic medication of clonidine, 3-4 mcg/kg, (group C), or place
bo (group S). In groups C and S, anesthesia was induced with inhalation of
sevoflurane-nitrous oxide. After tracheal intubation, anesthesia was mainta
ined with 2% end-tidal sevoflurane alone, In group A, each volunteer wore a
nose clip and breathed through a mouthpiece using a Mapleson D breathing s
ystem. The time-mean middle cerebral artery flow velocity (Vmca) was measur
ed during hypocapnia, normocapnia, and hypercapnia.
In groups S and C, the Vmca values were significantly lower than those of g
roup A at each PaCO2 level. The Vmca value of group C was significantly low
er than that of group S in hypercapnia, but not in hypocapnia or normocapni
a. The CO2 response slope of group C was significantly lower than those of
groups A and S.
The results indicate that clonidine, administered as an oral preanesthetic
medication, reduces Vmca in hypercapnia but not in hypocapnia or normocapni
a, and reduces the cerebrovascular CO2 response during sevoflurane anesthes