Best practice & research. Clinical anaesthesiology
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Best Pract Res Clin Anaesthesiol · Mar 2006
ReviewConcepts of EEG processing: from power spectrum to bispectrum, fractals, entropies and all that.
Over the past two decades, methods of processing the EEG for monitoring anaesthesia have greatly expanded. Whereas power spectral analysis was once the most important tool for extracting EEG monitoring variables, higher-order spectra, wavelet decomposition and especially methods used in the analysis of complex dynamical systems such as non-linear dissipative systems are nowadays attracting much attention. This chapter reviews some of these methods in brief. However, a comparison of some of the newer approaches with the more traditional ones with respect to clinical end-points by association measures and to the signal-to-noise ratio raises some doubt over whether the newer EEG-processing techniques really do better than the more traditional ones.
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Best Pract Res Clin Anaesthesiol · Mar 2006
ReviewSpecial cases: ketamine, nitrous oxide and xenon.
Most general anaesthetic agents produce anaesthesia by increasing the activity of inhibitory gamma-aminobutyric acid type A receptors. The effects of ketamine, xenon and nitrous oxide on these receptors are, however, negligible. These anaesthetic agents potently inhibit excitatory N-methyl-D-aspartate receptors. ⋯ However, xenon decreases the bispectral index in a concentration-dependent manner. Similarly, ketamine and nitrous oxide do not suppress the mid-latency auditory evoked potential whereas xenon does. Thus, anaesthetic depth monitors fail to describe consciousness accurately when ketamine and nitrous oxide are used.
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The concept of entropy, originally derived from thermodynamics, has been successfully applied to EEG analysis. Various entropy algorithms have been used in clinical studies, but until now a commercially available monitor exists only for spectral entropy. ⋯ Entropy guidance may not be used during ketamine or nitrous oxide administration, since there is no reliable correlation to the patient's state of consciousness. The usefulness of RE as a surrogate for increased EMG activity due to painful stimulation has not been proven so far.
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The era of research evaluating clinical outcomes associated with processed electroencephalogram (EEG) monitoring began with the first randomized trial of bispectral index monitoring (BIS) performed as part of the clearance process for approving routine clinical use of the BIS monitor by the United States Food and Drug Administration. Subsequent to this initial investigation, numerous other clinical investigations have demonstrated that the use of processed EEG monitors as an additional method of patient assessment and an aid to anaesthetic dosing can decrease anaesthetic usage and hasten recovery times. Because of the presumed association between anaesthetic effect and EEG changes, it is not surprising that the additional research has focused on the impact of processed EEG monitoring on postoperative outcomes and perioperative safety especially the prevention of intraoperative awareness.
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Best Pract Res Clin Anaesthesiol · Mar 2006
ReviewUse of cerebral monitoring during anaesthesia: effect on recovery profile.
This review article examines the effect of cerebral monitoring using an EEG-based device [i.e. bispectral index (BIS), patient state analyzer (PSA), auditory evoked potential (AEP), cerebral state index (CSI), or entropy] on titration of anaesthetic, analgesic and cardiovascular drugs during surgery. In addition, articles discussing the effects of these cerebral monitoring devices on recovery profiles following general anaesthesia, postoperative side effects, and anaesthetic costs are reviewed.