Effects of ketamine on isoflurane- and sevoflurane-induced cerebral vasodilation in rabbits.

Although ketamine has been reported to have little effect on the cerebral circulation when used with other anesthetics, its effect on the cerebral vascular response to volatile anesthetics, which increase cerebral blood flow in a concentration-dependent manner, remains obscure. A closed cranial window was prepared in 15 pentobarbital-anesthetized adult rabbits. The cerebral pial arteriolar alteration induced by either isoflurane (n = 8) or sevoflurane (n = 7) at 0 (before volatile anesthetic), 0.33, 0.67, and 1.0 minimum alveolar concentration (MAC) was measured under three consecutive conditions: intravenous infusion with saline, with ketamine, and with ketamine plus l-arginine. Ketamine reduced the vasodilation induced by 0.67 (120 +/- 9% versus 113 +/- 9%; P <.05) and 1.0 MAC isoflurane (136 +/- 11% versus 118 +/- 10%; P <.05), but l-arginine did not restore the isoflurane-induced cerebral vasodilation. In rabbits inhaling sevoflurane, the degree of cerebral vasodilator response was smaller than that by isoflurane, and the cerebral vasodilation was comparable whether in the presence or absence of ketamine (with or without l-arginine). In conclusion, ketamine reduces isoflurane-induced cerebral vasodilation, apparently independently of nitric oxide formation, while sevoflurane-induced cerebral vasodilation is not significantly affected by ketamine.