• A L Gaskell, D F Hight, J Winders, G Tran, A Defresne, V Bonhomme, A Raz, J W Sleigh, and R D Sanders.
• Department of Anaesthesia, Waikato Hospital, Hamilton, New Zealand.
• Br J Anaesth. 2017 Oct 1; 119 (4): 664-673.

BackgroundThe isolated forearm test (IFT) is the gold standard test of connected consciousness (awareness of the environment) during anaesthesia. The frontal alpha-delta EEG pattern (seen in slow wave sleep) is widely held to indicate anaesthetic-induced unconsciousness. A priori we proposed that one responder with the frontal alpha-delta EEG pattern would falsify this concept.MethodsFrontal EEG was recorded in a subset of patients from three centres participating in an international multicentre study of IFT responsiveness following tracheal intubation. Raw EEG waveforms were analysed for power-frequency spectra, depth-of-anaesthesia indices, permutation entropy, slow wave activity saturation and alpha-delta amplitude-phase coupling.ResultsVolitional responses to verbal command occurred in six out of 90 patients. Three responses occurred immediately following intubation in patients (from Sites 1 and 2) exhibiting an alpha-delta dominant (delta power >20 dB, alpha power >10 dB) EEG pattern. The power-frequency spectra obtained during these responses were similar to those of non-responders (P>0.05) at those sites. A further three responses occurred in (Site 3) patients not exhibiting the classic alpha-delta EEG pattern; these responses occurred later relative to intubation, and in patients had been co-administered ketamine and less volatile anaesthetic compared with Site 1 and 2 patients. None of the derived depth-of-anaesthesia indices could robustly discrimate IFT responders and non-responders.ConclusionsConnected consciousness can occur in the presence of the frontal alpha-delta EEG pattern during anaesthesia. Frontal EEG parameters do not readily discriminate volitional responsiveness (a marker of connected consciousness) and unresponsiveness during anaesthesia.Clinical Trial RegistrationNCT02248623.© The Author 2017. Published by Oxford University Press on behalf of the British Journal of Anaesthesia. All rights reserved. For Permissions, please email: journals.permissions@oup.com

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