Positron emission tomography study of regional cerebral blood flow and flow-metabolism coupling during general anaesthesia with xenon in humans

Background: The effects of xenon on regional cerebral blood flow (rCBF)are controversial. Moreover, the precise sites of action atwhich xenon exerts its effects in the human brain remain tobe established. Methods: rCBF was sequentially assessed by H₂¹⁵O positron emission tomographyin six volunteers. rCBF was determined at baseline and duringgeneral anaesthesia induced with propofol and maintained withone minimum alveolar concentration xenon. rCBF measurementswere started after the calculated plasma concentration of propofolhad decreased to subanaesthetic levels (<1.0 µg ml^–1).Changes in rCBF were calculated for 13 cerebral volumes of interestby measurement of a semi-quantitative perfusion index (PI).In addition, voxel-wise changes in rCBF were analysed usingstatistical parametric mapping. Results: Xenon had only minor effects on PI in grey matter volumes ofinterest. In contrast, PI was increased in white matter [from1.01 (0.11) to 1.24 (0.15) kcnt ml^–1 MBq^–1, P=0.05,mean (SD)]. Voxel-based analysis showed an increase of rCBFin white matter and a relative decrease of rCBF during xenonanaesthesia in distinct grey matter regions, particularly theorbito- and mesiofrontal cortex, cingulate gyrus, thalamus,hippocampus and bilateral cerebellum (P<0.05 corrected).When correlating PI with cerebral metabolic rate of glucose(previously obtained in another group of six volunteers using¹⁸F-fluorodeoxyglucose as tracer), the flow–metabolismcoupling was preserved during xenon anaesthesia. Conclusions: Xenon exerted distinct regional effects on CBF: relative decreasesin several cortical, subcortical, and cerebellar areas wereaccompanied by an increase in white matter. Flow–metabolismcoupling was not impaired during xenon anaesthesia.