EEG Entropy Research Articles

Entropy of EEG during anaesthetic induction: a comparative study with propofol or nitrous oxide as sole agent

The search continues for an anaesthetic monitor that can define the level of anaesthesia in an individual patient irrespective of anaesthetic agent(s) used. Studies of available monitors based on bispectral analysis or evoked auditory potentials show the complexity of the problem. We assessed a new monitor, based on the entropy of the EEG, during induction of anaesthesia with either propofol or nitrous oxide. In an open, randomized study (two groups; n=10) of day surgical patients, we induced loss of response with incremental boluses of propofol. The other group was given propofol 30 mg and then increasing concentrations of nitrous oxide until loss of response. We measured entropy with the M-Entropy Module S/5 (Datex-Ohmeda) using forehead electrodes and recorded response entropy (RE; including frontal electromyogram) and state entropy (SE; only the cortical EEG). Values are median (range). Baseline values were RE 98 (96-100), SE 89 (87-91) and RE 98 (96-99), SE 89 (87-91) for the propofol and nitrous oxide patients, respectively. During propofol induction, both entropy indices decreased with increasing sedation, with RE 40 (23-76) and SE 34 (17-70) at loss of response. Neither RE nor SE decreased during nitrous oxide inhalation, and at loss of response using nitrous oxide, RE and SE were unchanged at 98 (96-100) and 88 (85-91) respectively. The entropy monitor of anaesthetic depth shows a successive decrease with propofol but loss of consciousness with nitrous oxide is not associated with change in entropy indices.

Fractal spectrum, bispectrum, complexity, and entropy of EEG during anaesthesia

Fractal spectrum, bispectrum, complexity, and entropy of EEG during anaesthesia

Non-linear analysis of intracranial human EEG in temporal lobe epilepsy

Objective: Intracranial EEG recordings from patients suffering from medically intractable temporal lobe epilepsy were analyzed with the aim of characterizing the dynamics of EEG epochs recorded before and during a seizure and comparing the classification of the EEG epochs on the basis of visual inspection to the results of the numerical analysis.Methods: The stationarity of the selected EEGs was assessed qualitatively. The coarse-grained correlation dimension and coarse-grained correlation entropy were used for the non-linear characterization of the EEG epochs.Results: High-pass filtering was necessary in order to make the majority of the epochs appear stationarity beyond a time scale of about 2 s. It was found that the dimension of the ictal EEGs decreased with respect to the epochs containing ongoing (interictal) activity. The entropy of the ictal recordings however increased. A scaling of the entropy was applied and it was found that the scaled entropy of the ictal EEG decreased, consistent with the increased regularity of the ictal EEG. The coarse-grained quantities discriminated well between EEG epochs recorded prior to and during seizures at locations displaying ictal activity and classification improved by including the linear autocorrelation time in the analysis.Conclusions: It is concluded that ictal and non-ictal EEG can be well distinguished on the basis of non-linear analysis. The results are in good agreement with the visual analysis.