Sevoflurane 0.25 MAC preferentially affects higher order association areas: a functional magnetic resonance imaging study in volunteers.
BACKGROUND
Functional magnetic resonance imaging (fMRI) can objectively measure the subjective effects of anesthesia. Memory-related regions (association areas) are affected by subanesthetic doses of volatile anesthetics. In this study we measured the regional neuronal effects of 0.25 MAC sevoflurane in healthy volunteers and differentiated the effect between primary cortical regions and association areas.


METHODS
The effect of 0.25 MAC sevoflurane on visual, auditory, and motor activation was studied in 16 ASA I volunteers. With fMRI (3 Tesla Siemens magnetom), regional cerebral blood flow (rCBF) was measured by the pulsed arterial spin labeling technique. Subjects inhaled a mixture of O2 and 0.25 MAC sevoflurane and standard ASA monitoring was performed. Visual, auditory, and motor activation tasks were used. rCBF was measured in the awake state and during inhalation of 0.25 MAC sevoflurane, without and with activation. The change in rCBF (deltaCBF) with 0.25 MAC Sevoflurane during baseline state and with activation was calculated in 11 regions of interest related to visual, auditory, and motor activation tasks.


RESULTS
The change from baseline rCBF with 0.25 MAC sevoflurane was not statistically significant in the 11 regions of interest. With activation there was a significant increase in CBF in several regions. However, only in the primary and secondary visual cortices (V1, V2), thalamus, hippocampus, and supplementary motor area was the decrease in activation with 0.25 MAC sevoflurane statistically significant (P < 0.05).


CONCLUSIONS
Memory-related regions (association areas) are affected by subanesthetic concentrations of volatile anesthetics. Using fMRI, this study showed that 0.25 MAC sevoflurane predominantly affects the primary visual cortex, the related association cortex, and certain other higher order association cortices.
Ramani
Ramachandran
R
Department of Anesthesia, Yale University School of Medicine, New Haven, CT 06520-8051, USA. ramachandran.ramani@yale.edu
Qiu
Maolin
M
Constable
Robert Todd
RT
D000280:Administration, Inhalation; D000328:Adult; D018685:Anesthetics, Inhalation / Q000008:administration & dosage*; D001303:Auditory Cortex / Q000187:drug effects; D001931:Brain Mapping / Q000379:methods*; D002540:Cerebral Cortex / Q000098:blood supply / Q000187:drug effects* / Q000502:physiology; D002560:Cerebrovascular Circulation / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008568:Memory / Q000187:drug effects*; D008738:Methyl Ethers / Q000008:administration & dosage*; D009044:Motor Cortex / Q000187:drug effects; D012016:Reference Values; D000077149:Sevoflurane; D013113:Spin Labels; D014793:Visual Cortex / Q000187:drug effects
D018685:Anesthetics, Inhalation; D008738:Methyl Ethers; D013113:Spin Labels; D000077149:Sevoflurane
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