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ANESTHETIC PHARMACOLOGY

Sevoflurane 0.25 MAC Preferentially Affects Higher Order Association Areas: A Functional Magnetic Resonance Imaging Study in Volunteers

Ramachandran Ramani, MD^*, Maolin Qiu, PhD, and Robert Todd Constable, PhD

From the *Department of Anesthesia; and Magnetic Resonance Research Center, Yale University School of Medicine, New Haven, Connecticut.

Address correspondence and reprint requests to Ramachandran Ramani, MD, Department of Anesthesia, 333 Cedar Street, PO Box-208051, Yale University School of Medicine, New Haven, CT 06520-8051. Address e-mail to ramachandran.ramani{at}yale.edu.

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 (CBF) 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.

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				J. R. Sneyd and D. M. Mathews Memory and awareness during anaesthesia Br. J. Anaesth., June 1, 2008; 100(6): 742 - 744. [Full Text] [PDF]

Anesthesia & Analgesia® is published for the International Anesthesia Research Society® by Lippincott Williams & Wilkins with the assistance of Stanford University Libraries' HighWire Press®. Copyright 2006 by the International Anesthesia Research Society. Online ISSN: 1526-7598   Print ISSN: 0003-2999