Spectral entropy measurement of patient responsiveness during propofol and remifentanil. A comparison with the bispectral index †

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Abstract
Background. We compared two spectral entropies, state entropy (SE) and response entropy (RE), based on the irregularity of the EEG, to measure loss of response to verbal command (LORverbal) and noxious stimulus (LORnoxious) with the bispectral index (BIS) during propofol infusion with and without remifentanil. Methods. Three groups of 20 patients received an effect-site controlled propofol infusion (CePROP) starting at 1 µg ml−1 and increased in steps of 0.5 µg ml−1 at 4 min intervals. In addition, a remifentanil infusion was maintained at a group-dependent, fixed effect-site target concentration (CeREMI) (0, 2 or 4 ng ml−1). The ability of BIS, SE or RE to predict LORverbal and LORnoxious were compared with the changes in BIS, SE and RE using logistic regression, prediction probability (PK), and sensitivity/specificity. Results. In all groups, BIS, SE and RE decreased with increasing CePROP. However, BIS decreased more smoothly than SE and RE at deeper levels of sedation. At LORverbal, BIS50, SE50 and RE50 increased with increasing CeREMI. BIS, SE and RE all detected LORverbal accurately but BIS performed better at 100% sensitivity. Sensitivity/specificity for detection of LORverbal decreased for all methods with increasing CeREMI. LORnoxious was poorly described by all measures. Conclusion. LORverbal was detected accurately by BIS, SE and RE except for 100% sensitivity, where BIS performed better. Though BIS, SE and RE were influenced by remifentanil during propofol administration, their ability to detect LORverbal remained accurate. None of the measures predicted LORnoxious.