Facial muscle activity, Response Entropy, and State Entropy indices during noxious stimuli in propofol–nitrous oxide or propofol–nitrous oxide–remifentanil anaesthesia without neuromuscular block

Abstract

BackgroundEntropy™ is an anaesthetic EEG monitoring method, calculating two numerical parameters: State Entropy (SE, range 0–91) and Response Entropy (RE, range 0–100). Low Entropy numbers indicate unconsciousness. SE uses the frequency range 0.8–32 Hz, representing predominantly the EEG activity. RE is calculated at 0.8–47 Hz, consisting of both EEG and facial EMG. RE–SE difference (RE−SE) can indicate EMG, reflecting nociception. We studied RE−SE and EMG in patients anaesthetized without neuromuscular blockers.MethodsThirty-one women were studied in propofol–nitrous oxide (P) or propofol–nitrous oxide–remifentanil (PR) anaesthesia. Target SE value was 40–60. RE−SE was measured before and after endotracheal intubation, and before and after the commencement of surgery. The spectral content of the signal was analysed off-line. Appearance of EMG on EEG was verified visually.ResultsRE, SE, and RE−SE increased during intubation in both groups. Elevated RE was followed by increased SE values in most cases. In these patients, spectral analysis of the signal revealed increased activity starting from low (<20 Hz) frequency area up to the highest measured frequencies. This was associated with appearance of EMG in raw signal. No spectral alterations or EMG were seen in patients with stable Entropy values.ConclusionsIncreased RE is followed by increased SE at nociceptive stimuli in patients not receiving neuromuscular blockers. Owing to their overlapping power spectra, the contribution of EMG and EEG cannot be accurately separated with frequency analysis in the range of 10–40 Hz.

The Potential Application of Multiscale Entropy Analysis of Electroencephalography in Children with Neurological and Neuropsychiatric Disorders

“…Entropy is considered to be a method of detection of the system's randomness and predictability. In studies about the depth of anesthesia, entropy is higher when the patient is awake, while it is lower when the patient is in anesthesia [25]. The number of research works about the entropy of EEG in different neurological diseases has increased greatly in the past few years.…”

Application of Multivariate Empirical Mode Decomposition and Sample Entropy in EEG Signals via Artificial Neural Networks for Interpreting Depth of Anesthesia

“…If the entropy is large, it expressed that the patient status is awake. Response entropy (RE) and state entropy (SE) [9,10] are based on spectral entropy [11]. Spectral entropy uses FFT at first, however FFT is linear method so it might miss out some important imformation.…”

Spectral Entropy Parameters during Rapid Ventricular Pacing for Transcatheter Aortic Valve Implantation

“…Some studies suggest that muscle relaxation may confound EEG-based DoA monitoring. In the study of Aho et al [34] the increase in the RE after nociceptive stimulation was followed by increased SE in patients not receiving neuromuscular blockers. These increases were associated with the appearance of EMG in the EEG raw signal.…”

“…An increase in the EMG is an indicator of patient arousal, for example, in his/her response to nociception stimulation [12]. The RE entropy's shortest sampling window is 1.92 s, which allows the RE to respond quickly during the monitoring to EMG activation (32)(33)(34)(35)(36)(37)(38)(39)(40)(41)(42)(43)(44)(45)(46)(47). EMG is especially active during the awakened state but it may also be activated during surgery.…”