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SummaryPatient-maintained sedation is a mode of patient-controlled sedation during which propofol is administered using a target-controlled infusion, with patient demand increasing the target concentration. A system tested previously for safety in our institution resulted in oversedation. Aiming to improve safety, we modi®ed the system by increasing the lockout period to 4 min, reducing the starting concentration to 0.5 lg.ml )1 and the increments on demand to 0.1 lg.ml )1 . As in the previous study, healthy volunteers attempted to render themselves unconscious by frequently pressing the demand button. To assess effects on memory, volunteers were given keywords to remember every 15 min. The maximum target concentration reached varied between 1.0 and 2.5 lg.ml )1 . No volunteers lost consciousness, however, one volunteer had a brief period of apnoea and oxygen desaturation. The Cp50 for loss of memory for words was 1.26 lg.ml )1 . Although this version represents an improvement, we conclude that the system is not yet completely suitable for use without anaesthetic supervision.

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