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The coherent frequency - A measure of cognitive function during sedation
Jeevaratnum, R.D., Andrade, J., Sapsford, D.J., Pickworth, A. & Jones, J.G.
In: B. Bonke, J. Bovill N. Moerman (eds), Memory and Awareness in Anaesthesia
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Describes an experiment to validate the coherent frequency of the auditory evoked response as a measure of depth of anaesthesia. Subjects carried out a within-list recognition test at each of the six stages of the experiment, which were as follows: 1) awake, 2) low dose of the anaesthetic agent propofol, 3) higher dose of propofol, 4) the high dose of propofol plus electrical stimulation of the ulnar nerve, intended to increase arousal and hence to lighten sedation without altering the dose of anaesthetic, 5) the low dose of propofol again, 6) awake (recovery). Coherent frequency was measured at each of these stages. The results showed a highly significant correlation (r = .76, p < .001) between coherent frequency and performance on the within-list recognition task. We suggest that coherent frequency provides an objective measure of cognitive function during sedation, and is potentially useful as a monitor of depth of anaesthesia for both research and anaesthetic practice.