Functional brain imaging during anesthesia in humans - Effects of halothane on global and regional cerebral glucose metabolism

Background: Propofol and isoflurane anesthesia were studied previously with functional brain imaging in humans to begin identifying key brain areas in volved with mediating anesthetic-induced unconsciousness. The authors descr ibe an additional positron emission tomography study of halothane's ill viv o cerebral metabolic effects. Methods: Five male volunteers each underwent two positron emission tomograp hy scans. One scan assessed awake-baseline metabolism, and the other scan a ssessed metabolism during halothane anesthesia titrated to the point of unr esponsiveness (mean +/- SD, expired = 0.7 +/- 0.2%), Scans were obtained us ing a GE2048 scanner and the F-18 fluorodeoxyglucose technique. Regions of interest were analyzed for changes in both absolute and relative glucose me tabolism. In addition, relative changes in metabolism were evaluated using statistical parametric mapping, Results: Awake whole-brain metabolism averaged 6.3 +/- 1.2 mg.100 g(-1).min (-1) (mean +/- SD), Halothane reduced metabolism 40 +/- 9% to 3.7 +/- 0.6 m g.100 g(-1).min(-1) (P less than or equal to 0.005), Regional metabolism di d not increase in any brain areas for any volunteer. The statistical parame tric mapping analysis revealed significantly less relative metabolism in th e basal forebrain, thalamus, limbic system, cerebellum, and occiput during halothane anesthesia. Conclusions: Halothane caused a global whole-brain metabolic reduction with significant shifts in regional metabolism. Comparisons with previous studi es reveal similar absolute and relative metabolic effects for halothane and isoflurane, Propofol, however, was associated with larger absolute metabol ic reductions, suppression of relative cortical metabolism more than either inhalational agent, and significantly less suppression of relative basal g anglia and midbrain metabolism.