Awareness is a rare but in some cases severe complication of general anesthesia. In clinical practice vegetative signs such as sweating, lacrimation, tachycardia and hypertension are used to assess the anesthetic depth. Awareness however may also occur without any of these signs. Different systems based on the electroencephalogram (EEG) have been developed to monitor hypnosis. Some studies have shown that the use of EEG based monitor systems can reduce the incidence of awareness in patients of high risk. A similar reduction of the incidence was reached in studies using protocols based on concentrations of volatile anesthetics. Other systems to monitor anesthetic depth have been developed, but their influence on awareness has not yet been investigated sufficiently. Further studies are needed to clarify their impact concerning the incidence of awareness.
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