BJA Advance Access originally published online on November 23, 2007
British Journal of Anaesthesia 2008 100(1):66-71; doi:10.1093/bja/aem334
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Regional cerebral metabolic rate (positron emission tomography) during inhalation of nitrous oxide 50% in humans
1 Department of Anaesthesiology and Intensive Care
2 Department of Clinical Pharmacology
3 Department of Clinical Neurophysiology
4 Department of Radiation Physics
5 Department of Neurosurgery, University Hospital, S22185 Lund, Sweden
* Corresponding author: Department of Anaesthesia and Intensive Care, University Hospital, S22185 Lund, Sweden. E-mail: peter.reinstrup{at}med.lu.se
Background: Recent studies in man have shown that cerebral blood flow increases during inhalation of nitrous oxide (N2O), a finding which is believed to be a result of an increased cerebral metabolic rate (CMR). However, this has not previously been evaluated in man.
Methods: Regional CMRglu (rCMRglu) was measured three dimensionally with positron emission tomography (PET) after injection of 2-(18F)fluoro-2-deoxy-D-glucose in 10 spontaneously breathing men (mean age 31 yr) inhaling either N2O 50% in O2 30% or O2 30% in N2.
Results: Global CMRglu in young men was 27 (3) µmol 100 g–1 min–1 [mean (SD)]. Inhalation of N2O 50% did not change global CMRglu [30 (5) µmol 100 g–1 min–1] significantly, but it changed the distribution of the metabolism in the brain (P<0.0001 analysis of variance). Compared with inhalation of O2 30% in N2, N2O 50% inhalation increased the metabolism in the basal ganglia [14 (17)%, P<0.05] and thalamus [22 (23) %, P<0.05]. There was a prolonged metabolic effect of N2O inhalation seen on a succeeding PET scan with oxygen-enriched air (P<0.0001) performed 1 h after the N2O administration.
Conclusions: Inhalation of N2O 50% did not change global CMRglu, but the metabolism increased in central brain structures, an effect that was still present 1 h after discontinuation of N2O.
Keywords: anaesthetics, gases, N2O; brain, cerebral metabolic rate, regional cerebral metabolic rate; measurement technique, PET
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