Best practice & research. Clinical anaesthesiology
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Best Pract Res Clin Anaesthesiol · Sep 2007
Monitoring consciousness: the current status of EEG-based depth of anaesthesia monitors.
Direct and indirect inhibitory effects of anaesthetic agents on cortical activity are reflected in the electroencephalogram (EEG) as: (i) a shift from low-amplitude, high-frequency EEG, to high-amplitude, low-frequency activity (indicative of cortical depowering) and; (ii) the appearance of spindles and K-complexes (indicative of thalamocortical hyperpolarisation and sensory blockade). Existing EEG monitors use cortical activity as a proxy measure for consciousness. ⋯ Also the literature reveals many instances where the EEG pattern is dissociated from conscious state (e.g. an awake-looking EEG, but an unresponsive patient; or a slow-wave EEG in an awake patient). Fortunately, a slow-wave EEG (even in the presence of a responsive patient) usually indicates profound amnesia for explicit memory.
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Episodic memory is the most 'human' of all memory systems, is integrally related to the hippocampus, and not only permits memories of the past in rich detail, but also allows projection of thoughts into the future. However, episodic memory is very sensitive to anaesthetic drugs and cannot be formed during adequate general anaesthesia. ⋯ A more detailed understanding of episodic memory in relation to other memory systems, as well as the relationship of the hippocampus to episodic memory function is provided. A synthesis of diverse knowledge is undertaken to identify potential mechanisms of amnesic drug effect, which will, of course, require further research to delineate.
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Best Pract Res Clin Anaesthesiol · Sep 2007
Psychological consequences of awareness and their treatment.
Intraoperative awareness with subsequent recall is a rare but serious complication with an incidence of 0.1-0.2%. In approximately one third of the patients who have experienced awareness, late severe psychiatric sequelae may develop. The psychiatric symptoms in these patients fulfil the diagnostic criteria for post traumatic stress disorder. ⋯ The problem must be acknowledged. Professional psychiatric assessment and follow up should constitute standard practice. The treatments of choice are Eye Movement Desensitisation Reprocessing and Cognitive Behaviour Therapy.
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Dreaming during anaesthesia is defined as any recalled experience (excluding awareness) that occurred between induction of anaesthesia and the first moment of consciousness upon emergence. Dreaming is a commonly-reported side-effect of anaesthesia. The incidence is higher in patients who are interviewed immediately after anaesthesia (approximately 22%) than in those who are interviewed later (approximately 6%). ⋯ Most dreaming however, occurs in younger, fitter patients, who have high home dream recall, who receive propofol-based anaesthesia and who emerge rapidly from anaesthesia. Their dreams are usually short and pleasant, are related to work, family and recreation, are not related to inadequate anaesthesia and probably occur during recovery. Dreaming is a common, fascinating, usually pleasant and harmless phenomenon.