Best practice & research. Clinical anaesthesiology
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The SNAP electroencephalogram (EEG) monitor, described as an interesting, innovative EEG tool that samples raw EEG signals and uses its own unique algorithm, analyses both high- (80-420 Hz) and low- (0-20 Hz) frequency components of the signal. This is termed the SNAP index, and it ranges from 100 (arbitrarily representing the fully awake state) to 0 to provide functional data points for patient management. ⋯ Compared with other EEG devices, there is no evidence that SNAP is superior to others in generating more specific information about 'depth of sedation'. Moreover, the influence of high-frequency electromyographic activity on the SNAP needs to be clarified.
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The patient state index (PSI) is a clinically validated measure of the effect of anaesthesia and sedation. The PSI is calculated via a proprietary algorithm by a high-resolution 4-channel electroencephalograph (EEG) monitor after advanced artifact rejection. ⋯ The EEG monitor, initially called the PSA4000, is also the SEDLine monitor, the newest generation of the device. The SEDLine system provides the clinician the option of storing and downloading patient data for future use as well as monitoring bilateral brain function and symmetry with a density spectral array (DSA) display.
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Best Pract Res Clin Anaesthesiol · Mar 2006
ReviewAltered states of consciousness: processed EEG in mental disease.
Due to increasing life expectancy and a rising elderly population in Europe, the incidence of mild cognitive impairment which may predict diseases like Alzheimer's Disease or Vascular Dementia, is rising. Neurophysiological techniques are simple and inexpensive tools for early diagnosis and provide useful and objective correlates of cognitive activity both in normal subjects and patients suffering from the above conditions. Cognitive impairment due to different mental disease is characterized by decreased power and coherence in the alpha/beta band, which suggests functional disconnection among cortical areas, whereas both power and coherence in the delta and theta bands increase as a sign of cortical deafferentation from subcortical structures. Quantification of power and phase relationship by bispectral analysis suggests the Bispectral Index could be a useful but simple tool for early diagnosis of mental disease.
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This paper reviews a theory on the physiological conditions of consciousness. The theory consists of four hypotheses: (1) The occurrence of states of consciousness depends on the formation of higher-order representations that represent the internal state of the brain itself. (2) Higher-order representations are instantiated by the spatio-temporal activity pattern of large-scale neuronal assemblies. (3) The N-methyl-D-aspartate (NMDA) synapse plays a crucial role in the generation of conscious states by implementing the binding mechanism that the brain uses to produce large-scale assemblies. (4) The activation state of the NMDA receptor determines the rate at which representational structures can be built up. Unconsciousness or altered states of consciousness occur if, and only if, NMDA-dependent binding processes are inhibited.