“Paradoxical Arousal” During Isoflurane/Nitrous Oxide Anesthesia: Quantitative Topographical EEG Analysis

Abstract

Electroencephalogram (EEG) recordings have been used for the evaluation of drug effects on brain electrical activity, and numerous studies suggest that EEG measures may be useful for the assessment of depth of anesthesia [16, 22]. It has been shown that increases in depth of anesthesia may be reflected by the appearance of EEG slow-wave activity, and decreases in fast-wave activity [20]. Arousal reactions during emergence from anesthesia have been found to be associated with EEG desynchronization with a shift to higher frequencies. Controversy exists on the EEG response indicating intraoperative arousal phenomena. In anesthetized patients a shift to EEG delta activity concurrent with cardiac and respiratory irregularities has been interpreted as an indicator of insufficient depth of anesthesia. These intraoperative electrophysiological arousal phenomena have been addressed as “reverse” or “paradoxical” arousal phenomena [1]. However, brain electrical activity is modulated not only by drug effects but also by changes in respiratory and hemodynamic parameters, body temperature, and exogenous stimuli. Previous studies have shown that EEG high voltage slow waves may also occur spontaneously or in response to auditory or painful stimulation [6, 25].