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NEUROSURGICAL ANESTHESIA

Hypothermia Attenuates the Vasodilator Effects of Dexmedetomidine on Pial Vessels in Rabbits In Vivo

Hiroki Iida, MD^*, Mami Iida, MD, Hiroto Ohata, MD^*, Kiyoshi Nagase, MD^*, and Shuji Dohi, MD^*

*Department of Anesthesiology and Critical Care Medicine and Second Department of Internal Medicine and Anesthesiology, Gifu University School of Medicine, Gifu, Japan

Address correspondence and reprint requests to Hiroki Iida, MD, Department of Anesthesiology and Critical Care Medicine, Gifu University School of Medicine, 40 Tsukasamachi, Gifu-City, Gifu 500-8705, Japan. Address e-mail to iida{at}cc.gifu-u.ac.jp

Studies have indicated that mild to moderate hypothermia or dexmedetomidine may have neuroprotective properties in animal models. In this study, we investigated the effects of hypothermia on dexmedetomidine-induced responses in cerebral vessels in anesthetized rabbits by using the cranial-window preparation. After instrumentation under pentobarbital anesthesia, 12 rabbits were assigned to 1 of 2 equal groups: normothermic (nasopharyngeal and intrawindow temperature, 38.5°C–39.5°C) or hypothermic (33.0°C–34.0°C). Each rabbit received three different concentrations (10^-7, 10^-5, and 10^-3 M) of dexmedetomidine under the window, and cerebral pial vessel diameters were measured in a sequential manner. In the normothermic group, dexmedetomidine induced a significant concentration-dependent dilation in both large and small arterioles. In the hypothermia group, dexmedetomidine produced a U-shaped dose-response in both large and small cerebral arterioles (concentration-related vasoconstriction at 10^-7 and 10^-5 M, but vasodilation at 10^-3 M). In cerebral venules, a similar pattern of results was obtained, but changes were generally smaller than in arterioles. In conclusion, topically applied dexmedetomidine induces concentration-dependent dilation in cerebral arterioles in normothermic rabbits anesthetized with pentobarbital, but mild to moderate hypothermia attenuates these responses, with smaller dexmedetomidine concentrations causing vasoconstriction.

IMPLICATIONS: In normothermic rabbits anesthetized with pentobarbital, topically applied dexmedetomidine induces a concentration-dependent dilation in both large and small cerebral arterioles, but mild to moderate hypothermia attenuates these responses.