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
ReviewMonitoring consciousness in the pediatric patient: not just a small adult.
Intraoperative awareness, defined as postoperative memory for intraoperative events, is believed to occur about 0.2% of the time in a general adult surgical population. A recent large-scale prospective study from a single institution revealed a strikingly high incidence (0.8%) of intraoperative awareness in children aged 5-12 years although the sequelae of awareness during surgery in children were reported to be relatively minor. ⋯ To date, however, no monitor has been shown to be effective in detecting intraoperative awareness during surgery in pediatric patients. Further research is required to clarify the rates of intraoperative awareness in the pediatric population as well as the need for monitoring this event during the clinical practice of pediatric anesthesiology.