The effect of the alpha 2-agonist dexmedetomidine on the cerebral blood flow (CBF) and the metabolic rate for oxygen was studied by a sagittal sinus outflow technique in dogs during halothane anesthesia. Dexmedetomidine was given in a dose (10 micrograms/kg) reported to reduce the anesthetic requirement of halothane by 90%. During 0.9% halothane anesthesia dexmedetomidine caused a significant reduction in CBF without influencing the metabolic rate for oxygen. Reducing the halothane concentration to 0.1% caused no further change in CBF, but increased the metabolic rate for oxygen 19%. The cerebral vasoconstrictive effect, combined with the 90% reduction in MAC for halothane, indicates that dexmedetomidine might be a useful adjunct to inhalation anesthetics during neurosurgery in situations where an increase in CBF should be avoided.

Thirty-five patients undergoing cardiac surgery requiring cardiopulmonary bypass (CPB) were allocated randomly in a prospective double-blind study to receive either nimodipine 0.5 micrograms kg-1 min-1 or placebo. Cerebral blood flow (CBF) was measured during and immediately after CPB. Neuropsychological tests were performed 6 months after surgery to determine any relationship between ischaemic damage and CBF and administration of nimodipine. There were no differences in CBF between the nimodipine (n = 18) and placebo groups (n = 17). Significant changes in neuropsychological tests were found in six patients tested 6 months after surgery but there were no conclusive signs of ischaemic damage. The nimodipine-treated group performed better in tests of verbal fluency and visual retention, suggesting that some memory functions were preserved better in this group.