Sevoflurane 0.25 MAC preferentially affects higher order association areas: a functional magnetic resonance imaging study in volunteers

Abstract

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).

Conclusion: 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.

Figures

Figure 1

Schematic presentation of pulsed arterial spin labeling technique. White circle down arrows emerging from the arterial side represent the magnetized spins (protons). Some of the spins (gray circle arrows) flip back as they pass through the intracranial circulation. This proportion is a direct measure of circulation. Reproduced with permission from Golay X, Hendrikse J, Lim TCC. Perfusion imaging using arterial spin labeling. Top Magn Reson Imaging, 2004, 15, 10−27, ©Lippincott Williams & Wilkins.

Figure 2

Baseline regional cerebral blood flow (rCBF) (absolute) in the awake state (blue) and under 0.25 MAC sevoflurane (brown). Error bars indicate the standard deviations.

Figure 3

Percentage decrease in baseline regional cerebral blood flow (rCBF) (no activation) with 0.25 MAC sevoflurane anesthesia. Only supplementary motor area (SMA) shows an increase in rCBF. These changes were not statistically significant. Error bars indicate the standard deviations.

Figure 4

Percentage increase/decrease in regional cerebral blood flow (rCBF) with activation (visual/auditory/motor) in the awake state (blue) and under 0.25 MAC sevoflurane (brown). Error bars indicate the standard deviations. The decrease in activation (rCBF) was significant (marked*) in V1, V2, thalamus, hippocampus, and supplementary motor area (SMA); P < 0.05.

Figure 5

Shows the δCBF with visual/auditory activation in the awake state and with 0.25 MAC sevoflurane. Red/orange areas imply an increase in regional cerebral blood flow (rCBF) and purple areas a decrease in rCBF. Decrease in activity in the visual cortex (occipital region) with sevoflurane is seen.

Figure 6

Shows the δCBF with motor activation in awake state and with 0.25 MAC sevoflurane. Red/orange areas imply an increase in regional cerebral blood flow (rCBF) and purple areas a decrease in rCBF. Except for a decrease in rCBF in the visual cortex (because of the visual cue for motor activation) no other change was observed.