British journal of anaesthesia
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We have used Median Power Frequency (MPF) to study changes in the electroencephalogram during propofol infusions in 52 women about to undergo gynaecological surgery. Patients were allocated to receive propofol by one of nine different manually-controlled infusion schemes designed to achieve and maintain a stable blood propofol concentration between 1.0 and 6.0 micrograms ml-1, covering a range of states between conscious sedation and full anaesthesia. We recorded the changes in MPF and the response to clinical signs of loss of consciousness at these different doses and concentrations of propofol. ⋯ The EC50 for loss of consciousness was a propofol concentration of 2.3 (1.8-2.7) micrograms ml-1 and for 50% suppression of MPF was 3.1 (2.7-3.5) micrograms ml-1. The dose required for 50% suppression of MPF was 7.1 (6.2-8.0) mg kg-1 h-1. After 30 min, at blood propofol concentrations > 4.0 micrograms ml-1, consistent with stable anaesthesia, the mean MPF was 5.6 (4.5-6.3) Hz.
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We have defined the infusion dose requirements of propofol to suppress consciousness and response to a variety of graded non-noxious and noxious stimuli in 52 unpremedicated patients aged 16-40 yr and 32 patients aged 41-65 yr. They were allocated to receive one of five loading dose-infusion schemes designed to establish stable conditions covering the range from wakefulness, through sedation, to loss of consciousness and anaesthesia. ⋯ In both groups the dose-response curves for suppression of proprioception, finger counting and perception of light touch in conscious patients were shifted to the left of the curves for loss of consciousness and eyelash reflex. Dose-response curves for noxious stimuli were shifted to the right of those for loss of consciousness.