Wide inter-individual variability of bispectral index and spectral entropy at loss of consciousness during increasing concentrations of dexmedetomidine, propofol, and sevoflurane.

BACKGROUND The bispectral index (BIS) and the spectral entropy (state entropy, SE, and response entropy, RE) are depth-of-anaesthesia monitors derived from EEG and have been developed to measure the effects of anaesthetics on the cerebral cortex. We studied whether they can differentiate consciousness from unconsciousness during increasing doses of three different anaesthetic agents. METHODS Thirty healthy male volunteers aged 19-30 yr were recruited and divided into three 10-volunteer groups to receive either dexmedetomidine, propofol, or sevoflurane in escalating concentrations at 10 min intervals until loss of consciousness (LOC) was reached. Consciousness was tested at 5 min intervals and after drug discontinuation at 1 min intervals by requesting the subjects to open their eyes. LOC was defined as unresponsiveness to the request and pre-LOC as the last meaningful response. The first meaningful response to the request after drug discontinuation was defined as regaining of consciousness (ROC). For the statistical analysis, pre-LOC and ROC values were pooled to represent the responsive state while LOC values represented the unresponsive state. Prediction probability (P(K)) was estimated with the jack-knife method. RESULTS The lowest mean values for BIS, SE, and RE were recorded at LOC with all three drugs. The P(K) values were low for dexmedetomidine (BIS 0.62, SE 0.58, RE 0.59), propofol (BIS 0.73, SE 0.72, RE 0.72), and sevoflurane (BIS 0.70, SE 0.52, RE 0.62). CONCLUSIONS Because of wide inter-individual variability, BIS and entropy were not able to reliably differentiate consciousness from unconsciousness during and after stepwise increasing concentrations of dexmedetomidine, propofol, and sevoflurane.