An analysis of electroencephalogram activity across states of arousal in patients undergoing general anesthesia for carotid endarterectomy surgery
Tuesday, Nov 18, 2008, 10:00 AM -11:00 AM
*A. W. WOOD
, E. T. PIERCE
, A. CIMENSER
, P. L. PURDON
, M. V. SIMON
, R. CAMBRIA
, R. C. MERHAR
, J. KWO
, J. L. WALSH
, P. G. HARRELL
, E. N. BROWN
Harvard Med. Sch., Boston, MA;
Dept. of Anesthesia and Critical Care,
Martinos Ctr. for Biomed. Imaging,
Dept. of Neurol.,
Dept. of Vascular Surgery, Massachusetts Gen. Hosp., Boston, MA;
Dept. of Brain and Cognitive Sci.,
Div. of Hlth. Sci. and Technol., MIT, Cambridge, MA
Despite improvements in anesthetic drugs, EEG recording technology, and signal processing algorithms, there has been limited study to date of EEG changes across the stages of general anesthesia using full-montage EEG. The objective of this study is to develop more precise EEG-based neurophysiological correlates of arousal states under general anesthesia.
From the intraoperative monitoring database at Massachusetts General Hospital we identified 7 subjects who underwent carotid endarterectomy (CEA) surgery using a 10-20 system of EEG recordings to monitor for cerebral ischemia. The EEG recordings used were limited to those from subjects without a history of neurological or vascular problems (stroke, previous CEA) and whose CEA procedure was executed without anesthetic or surgical complication.
We used multitaper spectral methods to compute the time-varying power spectral density and coherence continuously throughout the entire operation. Average power spectral density and coherence were then calculated for shorter representative time segments corresponding to the following clinical states: baseline, induction, maintenance and recovery. Values were calculated in the delta (0-3.5Hz), theta (3.5-7.5Hz), alpha (7.5-12.5Hz), beta (12.5-25Hz) and gamma (25-100Hz) frequency bands.
During the baseline state, the EEGs displayed a uniform level of power in the theta through gamma band with a slightly higher level in the delta band. The induction and maintenance stages showed a drop in power across the gamma band and an increase in power in the alpha and beta bands. Upon recovery, the power spectrum returned to the baseline pattern. Inter-hemispheric and anterior-posterior coherence were high in the delta through alpha range and low in the beta through gamma range at baseline. During induction and maintenance, the coherence in the delta through alpha range was lost, but returned on recovery in 3 of 7 patients. Induction and maintenance also demonstrated a rise in beta through gamma coherence that was lost during the recovery state in all patients.
Our results show that, in addition to power spectral density, coherence changes appreciably between arousal states and could thus yield insight into neurophysiological correlates of awareness.
NIH/NCRR Grant M01-RR-01066
NIH/NINDS Grant K25NS057580-01A1
NIH/OD Grant DP1OD003646
NIH Grant R01 EB006385
Doris Duke Foundation Grant 2007081
[Authors]. [Abstract Title]. Program No. XXX.XX. 2008 Neuroscience Meeting Planner. Washington, DC: Society for Neuroscience, 2008. Online.
2008 Copyright by the Society for Neuroscience all rights reserved. Permission to republish any abstract or part of any abstract in any form must be obtained in writing by SfN office prior to publication.
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