Regional cerebral blood flow and glucose metabolism during propofol anaesthesia in healthy subjects studied with positron emission tomography.

Background: General anaesthetics can alter the relationship between regional cerebral glucose metabolism rate (rGMR) and regional cerebral blood flow (rCBF). With the present study, we wanted to assess quantitatively the effects of propofol on rCBF and rGMR in the same healthy volunteers measured with positron emission tomography (PET).

Methods: (15)O-labelled water and (18)F fluorodeoxyglucose were used as PET tracers to determine rCBF and rGMR, respectively, in eight healthy volunteers during the waking state (baseline) and during propofol anaesthesia. Propofol was titrated to keep a constant hypnotic depth (Bispectral Indes 35-40) throughout the anaesthesia. Changes in rGMR and rCBF were quantified using region-of-interest and voxel-based analyses.

Results: The measured mean propofol concentration was 4.1 ± 0.8 μg/ml during anaesthesia. Compared with the conscious state, total CBF and GMR decreased during the anaesthetic state with 47% and 54%, respectively. In the white and grey matter, rCBF and rGMR were reduced by 37% and 49%, and by 45% and 57%, respectively. Propofol decreased rCBF in all brain structures by 46-55% (P ≤ 0.01) with highest significant decreases in the thalamus and parietal lobe. Regional GMR was reduced in all brain areas to 48-66% (P ≤ 0.01) with highest significant reductions in the occipital lobe, the lingual gyrus, parietal lobe, temporal lobe and thalamus. No increases in rCBF or rGMR happened anywhere.

Conclusions: General anaesthesia with propofol is associated with a global metabolic and vascular depression in the human brain, with significant shifts in regional blood flow and metabolism indicating marked metabolic and vascular responsiveness in some cortical areas and thalamus.