Background Both basic and clinical consciousness research aims to find objective measures that reliably distinguish conscious from unconscious brain states. Electroencephalogram (EEG) measures are widely used, although they may be contaminated by electrical signals from muscles.

Methods To assess this source of error, we investigated the impact of neuromuscular blockade (NMB) on proposed measures of consciousness (spectral slope, Lempel-Ziv complexity (LZc), connectivity, alpha peak frequency, power in canonical EEG frequency bands) computed from spontaneous high-density EEG recorded from six healthy volunteers in three different conditions: (1) awake-unparalysed, (2) awake-paralysed caused by neuromuscular blocking agent (NMBA), and (3) sedated-paralysed (sedated with propofol, paralysed by NMBA, (un)consciousness non-confirmable).

Results The markers we investigated distinguished awake-unparalysed states from sedated-paralysed with close to perfect accuracy. Our analysis revealed a serious failure of all measures, except alpha power, to recognise awake-paralysed, without sedation, as an aware state. Errors ranged from 19% of awake-paralysed time segments predicted as unaware (using spectral slope) to 100% (using LZc). Using alpha power, only 1% of all awake-paralysed segments were misclassified. Critically, the awake-paralysed is the state that is important to detect in sedated-paralysed patients, to prevent the experience of accidental awareness during general anaesthesia (AAGA).

Conclusions This study clearly demonstrates that many EEG-based measures fail to recognise awareness in awake-paralysed subjects, by using a unique high-density EEG data set. Alpha power was determined to be the most robust measure to detect AAGA, but this may not generalise to all types of general anaesthetic agents.

The authors have declared no competing interest.

This analysis was funded by three grants awarded to JFS: ConsciousBrainConcepts project under the Life Science Convergence Projects initiative of the University of Oslo, the European Union Horizon 2020 Framework Programme for Research and Innovation under the Specific Grant Agreements No. 945539 (Human Brain Project SGA3), No. 785907 (Human Brain Project SGA2; JFS, ASN, BEJ), and the Norwegian Research Council (NRC grant 262950/F20 and FRIPRO 335828).

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The study was approved by the Southern Adelaide Clinical Human Research Ethics Committee. Participants gave written, informed consent for the procedures.

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