Depth of Anaesthesia: Measuring or guessing?

Abstract

Abstract-This paper is a comprehensive literature review on the Depth of Anaesthesia (DoA) monitoring problem. We first investigate the current clinical practice, then briefly introduce the DoA monitors, finally we analyse and discuss the reliability and accuracy of current DoA assessment practice. In this study we find that most of the responses suppressed by anaestheic agents are not of the central nervous system (CNS) but are responses from the peripheral nervous systems (PNS). The responses generated for drug combinations across the therapeutic ranges show considerable variations in drug concentrations that constitute adequate anaesthesia for a particular stimulus. We propose to capture the decision process of anaesthetist using neural networks as neural networks are good at finding patterns in non linear, non stationary signals.

Signal processing and machine learning algorithm to classify anaesthesia depth

“…The present study developed an algorithm that jointly considers changes in ANS and CNS pattern activity, to classify AD. Most devices used to assess anaesthetic effects on cerebral activity rely on EEG-based indices with ambiguity in reduction of intraoperative awareness 14 21 37. Among the most used EEG-based indices, one finds entropy and Bispectral Index 38.…”

“…Assessment of AD through clinical signs such as state of consciousness, limb movement, heart rate, pupil size, blood pressure, arterial blood oxygen and perspiration is used in general anaesthesia because it reflects the activity of the autonomic nervous system (ANS) and central nervous system (CNS) 13. Evoked potentials, entropy which include state entropy (SE) and response entropy (RE), Bispectral Index and Narcotrend indices are objective measurements of the activity of the ANS 14. All these indices are based on different algorithms that analyse and record changes in electroencephalography (EEG) signals and convert them into numerical values that correspond to certain levels of unconsciousness 15–19.…”

“…Burst suppression pattern appears during deep anaesthetic levels, which may be interpreted as an error by the Bispectral Index and entropy indices22 24; causing a false estimation of AD, and decreasing the safety margin between anaesthetic administration and optimal anaesthetic level 22 23 25–27. Another issue is that the previously mentioned indices and devices do not take into consideration ANS variables as part of the EEG indices used in DA level quantification and classification 14 28. Therefore, there is no definitive gold standard for the evaluation of AD levels during surgery or intensive care units 20 29.…”

“… 15–19 Despite quantification of anaesthetic levels by these new technologies, there are issues such as reports of ambiguity in the reduction of intraoperative awareness and burst suppression pattern misinterpretation. 14 20–23 …”

Variability of anesthetic depth in total intravenous anesthesia vs balanced anesthesia using entropy indices: a randomized, crossover, controlled clinical trial

“…5,6 To avoid intraoperative awakening, cortical activity monitoring via electroencephalography (EEG) is used. Systems such as the bispectral index (BIS), 7 entropy recordings (M-Entropy), 8,9 and auditory evoked potentials 10 have guided the knowledge of the patient's degree of unconsciousness.…”