Invariant reversible QEEG effects of anesthetics

Continuous recordings of brain electrical activity were obtained from a gro up of 176 patients throughout surgical procedures using general anesthesia. Artifact-free data from the 19 electrodes of the International 10/20 Syste m were subjected to quantitative analysis of the electroencephalogram (QEEG ). Induction was variously accomplished with etomidate, propofol or thiopen tal. Anesthesia was maintained throughout the procedures by isoflurane, des flurane or sevoflurane: (N = 68), total intravenous anesthesia using propof ol (N = 49), or nitrous oxide plus narcotics (N = 59). A set of QEEG measur es were found which reversibly displayed high heterogeneity of variance bet ween four states as follows: (1) during induction; (2) just alter loss of c onsciousness (LOC); (3) just before return of consciousness (ROC); (4) just alter ROC. Homogeneity of variance across all agents within states was fou nd. Topographic statistical probability images were compared between states . At LOC, power increased in all frequency bands in the power spectrum with the exception of a decrease in gamma activity, and there was a marked ante riorization of power. Additionally, a significant change occurred in hemisp heric relationships, with prefrontal and frontal regions of each hemisphere becoming more closely coupled, and anterior and posterior regions on each hemisphere, as well as homologous regions between the two hemispheres, unco upling. All of these changes reversed upon ROC. Variable resolution electro magnetic tomography (VARETA) was performed to localize salient features of power anteriorization in three dimensions. A common set of neuroanatomical regions appeared to be the locus of the most probable generators of the obs erved EEG changes, (C) 2001 Academic Press.