BIS and spectral entropy monitoring during sedation with midazolam/remifentanil and dexmedetomidine/remifentanil

Anthony R Absalom,David K Menon

doi:10.1186/cc7776

Abstract

Haenggi and colleagues report considerable intra- and inter-individual variability in derived electroencephalogram (EEG) parameters (Bispectral Index (BIS), response entropy and state entropy) recorded in volunteers sedated with midazolam or dexmedetomidine infusions titrated to modified Ramsay scores of 2, 3 and 4, and a remifentanil infusion at a fixed target concentration. Possible explanations for the low, variable and fluctuating EEG parameters are that volunteers were intermittently asleep, and that remifentanil gave rise to a low amplitude, slowed EEG pattern despite maintained consciousness. BIS and entropy values should be interpreted in combination with clinical findings in patients sedated with these agents.

Highlights

Individualised titration of sedation on the intensive care unit has many benefits, but requires a reliable, objective method of assessing sedation level
Can we explain the marked variability in Bispectral Index (BIS) and entropy readings, which in some cases rapidly oscillated between values associated with consciousness and values associated with surgical planes of anaesthesia? BIS and entropy monitors were designed to correlate EEG signals with anaesthetists’ impressions of depth of sedation and anaesthesia across a wide range of clinical states
Design of these monitors includes the assumption that increasing doses of sedative or hypnotic drugs are associated with a continuum of changes in one or more aspects of cerebral electrical activity that correlate with depth of sedation and anaesthesia

Summary

Introduction

Individualised titration of sedation on the intensive care unit has many benefits, but requires a reliable, objective method of assessing sedation level. BIS and entropy monitors were designed to correlate EEG signals with anaesthetists’ impressions of depth of sedation and anaesthesia across a wide range of clinical states. Design of these monitors includes the assumption that increasing doses of sedative or hypnotic drugs are associated with a continuum of changes in one or more aspects of cerebral electrical activity (such as amplitude, spectral content or bicoherence [5,6]) that correlate with depth of sedation and anaesthesia.

Results

Conclusion