A COMPARISON OF THE ELECTROPHYSIOLOGIC CHARACTERISTICS OF EEG BURST-SUPPRESSION AS PRODUCED BY ISOFLURANE, THIOPENTAL, ETOMIDATE, AND PROPOFOL

Electroencephalogram (EEG) burst-suppression can be produced with seve ral anesthetic agents. Discussions of burst-suppression suggest that i t has been viewed by many as a relatively uniform physiologic state in dependent of the agent used to produce it. This view may be an oversim plification. In this study, relatively deep EEG burst-suppression (sup pression to burst time ratio, 4:1) was induced in rats with isoflurane (I), thiopental (T), etomidate (E), and propofol (P). Burst duration, maximum peak-to-peak voltage, area under the curve, and the ratio of power in high versus low frequencies of EEG recorded in both cortex an d subcortex (thalamus) were determined. Analysis of the bursts reveale d significant differences in duration [I, 1.4 +/- 0.4 (SD); T, 0.8 +/- 0.5; E, 0.3 +/- 0.1; P, 0.4 +/- 0.1 seconds], peak-to-peak voltage (I , 488 +/- 146; T, 285 +/- 106; E, 310 +/- 87; P, 249 +/- 50 mu V), and area under the curve (I, 111 +/- 24; T, 35 +/- 31; E, 17 +/- 7; P, 21 +/- 4 mu V-s) for all agent pairs except etomidate and propofol. Supp ression phase analysis revealed considerable residual activity with al l four agents, although peak-to-peak voltage (I, 129 +/- 29; T, 64 +/- 20; E, 62 +/- 11; P, 40 +/- 15 mu V) and area under the curve (I, 73 +/- 17; T, 37 +/- 14; E, 30 +/- 5; P, 22 +/- 10 mu V-S) Were greatest with isoflurane. The cortical versus subcortical comparison revealed, for all agents, greater peak-to-peak voltage and area under the curve in the subcortex. The data indicate that the electrophysiologic charac teristics of burst-suppression vary among the four agents, with the po ssible exception of etomidate and propofol. The data suggest that the neurophysiologic states associated with burst-suppression produced by various anesthetics should not be assumed to be uniform.