Best practice & research. Clinical anaesthesiology
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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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The Narcotrend (MonitorTechnik, Bad Bramstedt, Germany) is an EEG monitor designed to measure the depth of anaesthesia. It has been developed at the University Medical School of Hannover, Germany, has been commercially available for 5 years and has meanwhile received US Food and Drug Administration approval. The Narcotrend algorithm is based on pattern recognition of the raw electroencephalogram (EEG) and classifies the EEG traces into different stages from A (awake) to F (increasing burst suppression down to electrical silence). ⋯ The raw EEG signal can be recorded by standard electrocardiogram electrodes for single- and double-channel registration. The Narcotrend monitor provides a vast amount of information: the actual Narcotrend stage and index, the trend ('cerebrogram'), the raw EEG signal and a power spectrum and several derived EEG parameters. Multiple clinical and validation studies are available for the Narcotrend monitor, including comparisons with the BIS monitor (Aspect Medical Systems, Natick, USA).
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Analgesia (pain relief) amnesia (loss of memory) and immobilisation are the three major components of anaesthesia. The perception of pain, and therefore, the need for analgesia, is individual, and the monitoring of analgesia is indirect and, in essence, of the moment. Under general anaesthesia, analgesia is continually influenced by external stimuli and the administration of analgesic drugs, and cannot be really separated from anaesthesia: the interaction between analgesia and anaesthesia is inescapable. ⋯ For the past few years, automated electroencephalographic analysis has been of great interest in monitoring anaesthesia and could be useful in adapting the peroperative administration of opioids. A range of information collected from the electroencephalogram, haemodynamic readings and pulse plethysmography might be necessary for monitoring the level of nociception during anaesthesia. Information theory, multimodal monitoring, and signal processing and integration are the basis of future monitoring.
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Best Pract Res Clin Anaesthesiol · Mar 2006
ReviewAnaesthesia defined (gentlemen, this is no humbug).
Our charge was to define anaesthesia as produced by inhaled anaesthetics. A definition may be useful to an understanding of the anaesthetic state, and it may guide studies of the mechanisms by which anaesthesia is produced. ⋯ Some conditions are unmeasurable (unconsciousness), not present for all inhaled anaesthetics (relaxation), or are not present at anaesthetizing concentrations (suppression of autonomic reflexes.) One (analgesia) is unmeasurable (the anaesthetized patient cannot tell an investigator that he/she hurts or does not hurt), and surrogate measures (increases in breathing, blood pressure, and heart rate with surgery) suggest that some pain is perceived. These and myriad other changes produced by inhaled anaesthetics are side effects; they do not define anaesthesia; only immobility and amnesia supply such a definition.