POSITRON EMISSION TOMOGRAPHY STUDY OF REGIONAL CEREBRAL METABOLISM INHUMANS DURING ISOFLURANE ANESTHESIA

Background: Although the anesthetic effects of the intravenous anesthe tic agent propofol have been studied in the living human brain using b rain imaging technology, the nature of the anesthetic state evident in the human brain during inhalational anesthesia remains unknown. To ex amine this issue, the authors studied the effects of isoflurane anesth esia on human cerebral glucose metabolism using positron emission tomo graphy (PET). Methods: Five volunteers each underwent two PET scans; o ne scan assessed awake-baseline metabolism and the other scan assessed metabolism during isoflurane anesthesia titrated to the point of unre sponsiveness (means +/- SD; expired = 0.5 +/- 0.1%). Scans were obtain ed with a GE2048 scanner (4.5-mm resolution-FWHM) using the (18)fluoro deoxyglucose technique. Results: Awake whole-brain glucose metabolism averaged 69 +/- 1.5 mg . 100 g(-1). min(-1) (means +/- SD), Isoflurane reduced whole-brain metabolism 46 +/- 11% to 3.6 +/- 0.3 mg . 100 g(- 1). min(-1) (P less than or equal to 0.005), Regional metabolism decre ased fairly uniformly throughout the brain, and no evidence of any reg ional metabolic increases were found in any brain region for any parti cipant. A region-of-interest analysis showed that the pattern of regio nal metabolism evident during isoflurane anesthesia was not significan tly different from that seen when participants were awake. Conclusion: These data clarify that the anesthetic state evident in the living hu man brain during unresponsiveness induced with isoflurane is associate d with a global, fairly uniform, whole-brain glucose metabolic reducti on of 46 +/- 11%.