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Understanding anesthesia through functional imaging

Ramani, Ramachandran; Wardhan, Richa

Current Opinion in Anaesthesiology:
doi: 10.1097/ACO.0b013e32830edbf3
Neuroanesthesia: Edited by Arthur Lam
Abstract

Purpose of review: This review will highlight the recent functional magnetic resonance imaging, positron emission tomogram scan and connectivity studies in anesthesia and analgesia.

Recent findings: In regional cerebral blood flow (rCBF) studies with isoflurane and sevoflurane, there is a consistent pattern of rise in rCBF in the anterior cingulate cortex and insula while the thalamus, lingual cortex and cerebellum show a decrease in rCBF, in a dose range of 0.2–1 minimum alveolar concentration. Even 0.25 minimum alveolar concentration causes a predominant decrease of rCBF in the cortical regions and increase of rCBF in the subcortical regions. This minimum alveolar concentration level primarily affects the association cortices. Thalamus and thalamo-cortical pathways seem to be linked to the hypnotic effects of anesthesia and deep sedation. Connectivity studies also confirm this. The electroencephalogram equivalent of this appears to be a transition from ‘α’ wave activity to ‘δ’ wave activity. Anterior cingulate cortex, S1 and S2 are the regions consistently activated in acute pain. Remifentanil infusion in acute pain decreases the activation in pain perception regions while activating the pain modulation regions. In chronic pain states, prefrontal cortex and insula are activated whereas there is a decrease in activity in the thalamus.

Summary: Slowly, a pattern of neuronal activity reflecting hypnosis, analgesia, amnesia and reflex suppression seems to be emerging giving us a better insight into the central nervous system effects of anesthesia.

Author Information

Yale University School of Medicine, New Haven, Connecticut, USA

Correspondence to Ramachandran Ramani, MD, Assistant Professor of Anesthesia, Yale University School of Medicine, 333 Cedar Street, PO Box 208051, New Haven, CT 06520-8051, USA Tel: +1 203 785 2802; fax: +1 203 785 6664; e-mail: ramachandran.ramani@yale.edu

© 2008 Lippincott Williams & Wilkins, Inc.