CEREBRAL METABOLISM DURING PROPOFOL ANESTHESIA IN HUMANS STUDIED WITHPOSITRON EMISSION TOMOGRAPHY

Background: Although the effects of propofol on cerebral metabolism ha ve been studied in animals, these effects have yet to be directly exam ined in humans. Consequently, we used positron emission tomography (PE T) to demonstrate in vivo the regional cerebral metabolic changes that occur in humans during propofol anesthesia, Methods: Six volunteers e ach underwent two PET scans; one scan assessed awake-baseline metaboli sm, and the other assessed metabolism during anesthesia with a propofo l infusion titrated to the point of unresponsiveness (mean rate +/- SD = 7.8 +/- 1.5 mg.kg(-1).h(-1)). Scans were obtained using the (18)flu orodeoxyglucose technique. Results: Awake whole-brain glucose metaboli c rates (GMR) averaged 29 +/- 8 mu moles.100g(-1)min(-1) (mean +/- SD) . Anesthetized whole-brain GMR averaged 13 +/- 4 mu moles.100g(-1).min (-1) (paired t test, P less than or equal to 0.007), GMR decreased in all measured areas during anesthesia. However, the decrease in GMR was not uniform. Cortical metabolism was depressed 58%, whereas subcortic al metabolism was depressed 48% (P less than or equal to 0.001). Marke d differences within cortical regions also occurred. In the medial and subcortical regions, the largest percent decreases occurred in the le ft anterior cingulate and the inferior colliculus. Conclusion: Propofo l produced a global metabolic depression on the human central nervous system, The metabolic pattern evident during anesthesia was reproducib le and differed from that seen in the awake condition. These findings are consistent with those from previous animal studies and suggest PET may be useful for investigating the mechanisms of anesthesia in human s.