Mild hypothermia can enhance pial arteriolar vasodilation induced by isoflurane and sevoflurane in cats.

OBJECTIVE

Volatile anesthetics have been shown to dilate cerebral vessels. Recent evidence suggests that mild hypothermia can alter vascular reactivity of the cerebral vessels. However, the effect of mild hypothermia on volatile anesthetic-induced vasodilation of cerebral vessels is unknown. In the present study, we investigated the effect of mild hypothermia on pial arteriolar vasodilation induced by isoflurane and sevoflurane in cats.

DESIGN

Prospective, randomized, experimental study with repeated measures.

SETTING

Investigational animal laboratory.

SUBJECTS

Forty cats were used for the study of systemic administration of volatile anesthetics, and 22 cats were used for the study of topical administration of volatile anesthetics.

INTERVENTIONS

This study was approved by the Animal Experiment Committee of Nara Medical University. Animals were anesthetized with pentobarbital to maintain suppressive electroencephalographic patterns, which were introduced to measure direct effects of anesthetic agents after removing metabolic effects. The cranial window technique, combined with microscopic video recording, was used for the measurement of small (50-100 microm) and large (100-200 microm) pial arteriolar diameter in an experiment. Animals were randomly assigned to either a normothermic (37 degrees C) or a hypothermic group (33 degrees C). Desired temperatures were maintained by using a water blanket. In the first phase of the study, the effect of hypothermia on pial arteriolar vasodilation induced by systemic administration of isoflurane or sevoflurane was assessed. Each cat received isoflurane or sevoflurane at 0.5, 1.0, 1.5, and 2.0 minimum alveolar anesthetic concentrations, and the diameter of pial arterioles was measured. In the second group of animals, the direct effect of isoflurane and sevoflurane on pial vessels was evaluated. The artificial cerebrospinal fluid bubbled with isoflurane or sevoflurane (minimum alveolar anesthetic concentrations of 1 or 3) was topically administered in the cranial window.

MEASUREMENTS AND MAIN RESULTS

Systemic and topical administration of isoflurane and sevoflurane produced significant dilation of both small and large pial arterioles in a dose-dependent manner during normothermia. In the hypothermic group, vasodilation of small pial arterioles by systemic administration of isoflurane and sevoflurane at a high concentration was significantly larger than in the normothermic group (p <.05). Vasodilation of both small and large pial arterioles by topical administration of isoflurane and sevoflurane was significantly greater in the hypothermic group than in the normothermic group (p <.05).

CONCLUSIONS

These results suggest that pial arteriolar vasodilation induced by isoflurane and sevoflurane can be enhanced by mild hypothermia in cats anesthetized with pentobarbital.