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Isoflurane anesthesia blunts cerebral responses to noxious and innocuous stimuli: a fMRI study
J F Antognini1, M H Buonocore, E A Disbrow
1Department of Anesthesiology, University of California, Davis 95616, USA. jfantognini@ucdavis.edu
Abstract:
We used functional magnetic resonance imaging to determine how isoflurane affected cerebral neuronal activation resulting from noxious and innocuous stimuli. Five male volunteers were subjected to mild electrical shock and tactile stimuli applied to the hand. During low (0.7%) and moderate (1.3%) isoflurane anesthesia the stimuli were repeated and a supramaximal electrical shock was also applied. Tactile stimulation activated bilateral SI and SII, but resulted in no significant activation at low or moderate anesthesia. Electrical shock activated contralateral SI and bilateral SII; low anesthesia completely abolished this response. The supramaximal stimulus activated the caudate nucleus and bilateral thalamus at low anesthesia; these responses were diminished at moderate anesthesia. Isoflurane anesthesia blunts cerebral responses to somatosensory stimuli, and the absence of cortical activation during supramaximal stimulation suggests that noxious-induced movement is generated in lower CNS structures.
Insights
Isoflurane anesthesia significantly reduces brain responses to touch and pain. Even strong painful stimuli may not activate the cortex under anesthesia, suggesting pain processing occurs in lower brain areas.
Area of Science:
- Neuroscience
- Anesthesiology
- Neuroimaging
Background:
- Understanding how anesthetics affect brain activity is crucial for patient safety.
- Isoflurane is a widely used inhalational anesthetic.
- Cerebral neuronal activation patterns in response to stimuli under anesthesia require further elucidation.
Purpose of the Study:
- To investigate the impact of isoflurane anesthesia on cerebral neuronal activation.
- To differentiate responses to noxious and innocuous stimuli during varying levels of isoflurane anesthesia.
Main Methods:
- Functional magnetic resonance imaging (fMRI) was employed in five male volunteers.
- Stimuli included tactile, mild electrical shock, and supramaximal electrical shock applied to the hand.
- fMRI data were acquired during low (0.7%) and moderate (1.3%) isoflurane anesthesia.
Main Results:
- Tactile stimulation activated bilateral SI and SII but showed no significant activation under anesthesia.
- Mild electrical shock activated contralateral SI and bilateral SII; this was abolished at low anesthesia.
- Supramaximal stimulus activated the caudate nucleus and thalamus at low anesthesia, with diminished responses at moderate anesthesia.
Conclusions:
- Isoflurane anesthesia blunts cerebral responses to somatosensory stimuli.
- Absence of cortical activation during supramaximal stimulation suggests noxious-induced movement originates in lower central nervous system (CNS) structures.