Best practice & research. Clinical anaesthesiology
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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.
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This chapter will focus on the two auditory evoked potentials (AEP) most commonly used to assess the effects of general anesthetics on the brain, the auditory middle latency response (AMLR) and the 40 Hz auditory steady-state response (40 Hz-ASSR). We will review their physiological basis, the recording methodology, the effects of general anesthetics, their ability to track changes in level of consciousness and their clinical applications. Because of space constraints, this review will be limited to human studies.
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Best Pract Res Clin Anaesthesiol · Mar 2006
ReviewMonitoring consciousness in intensive care medicine.
Sedation and analgesia are important components of care for critically ill patients. Avoiding over-as well as undersedation is of utmost importance as both states carry considerable risks and may influence outcome. The management of sedation has changed dramatically over the past two decades from providing a dosage level by which the patient was kept in a deep stage of anaesthesia to a current dosing strategy allowing the administration of drugs in line with individual need, resulting in most cases in a slightly sedated, cooperative patient. ⋯ Accordingly, most results from studies evaluating the performance of processed EEG parameters in critically ill patients have not been satisfactory. At present, monitoring sedation with processed EEG parameters cannot generally be recommended. However, in special situations such as deep sedation and neuromuscular blockade, in which clinical sedation scales are prone to failure, the bispectral index may help to assess the level of sedation.