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Br J Anaesth. 2007 Oct;99(4):532-7. Epub 2007 Jul 24.

Can anaesthetists be taught to interpret the effects of general anaesthesia on the electroencephalogram? Comparison of performance with the BIS and spectral entropy.

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  • 1Department of Anaesthesia, Waikato Hospital, Hamilton, New Zealand.



Unlike the other physiological waveforms monitored in anaesthesia, the EEG lacks a regularly repeating pattern, implying that it would be very difficult for an anaesthetist to obtain any useful information from the raw EEG. There are, however, clear changes in the EEG caused by GABA-ergic anaesthetic agents. The anaesthetized EEG still looks like a random waveform, but clearly a different random waveform from that seen when conscious.


The aim of this study was to assess how 40 anaesthetists would perform at interpreting intra-operative EEGs compared with two processed EEG (pEEG) monitors, BIS and entropy, after a short educational presentation. Short segments of EEGs were used from the pre-induction phase, the intra-operative phase with adequate surgical anaesthesia, and the transition phase between these two states.


While anaesthetists' performance varied widely, most could reliably differentiate an anaesthetized from a conscious EEG. Further, both humans (41% wrong) and machines (30% wrong) made mistakes. Unlike the anaesthetists, the pEEG monitors did not make a major error (i.e. producing a number in the conscious range (>85) when analysing an anaesthetized EEG or the converse error).


A brief PowerPoint presentation enables anaesthetists to recognize the effects on the EEG of GABA-ergic anaesthetic agents. In the clinical context, it remains likely that the combination of a pEEG monitor that clearly presents the EEG and a clinician who has a good, basic understanding of, and a willingness to look at, the raw EEG will result in more accurate interpretation of the intra-operative EEG.

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