SummaryWe have designed a new effect-site controlled, patient-maintained sedation system for delivering propofol. In the previous systems we developed, the patients retained the use of the handset throughout the procedure and were able to increase the level of sedation. However, it was found that this could potentially lead to oversedation. In the present system, the patients were able to increase their level of sedation until a level was reached that was judged by the patients as being adequate to allow them to tolerate the injection of dental local anaesthetic. The handset was then taken from the patients and the effect site concentration of propofol was maintained at that level for the remainder of the procedure. To assess its safety and efficacy, the system was used to sedate 40 patients presenting for dental procedures under sedation. The system was used successfully and treatment was completed in 39 patients. The system was found to be safe. Both surgeon and patient approval scores were high. Although this study demonstrates the efficacy of effect-site controlled, patient-maintained propofol sedation in this group of patients, further work is required to confirm its safety. At present, patients receiving conscious sedation in the UK for dental procedures usually receive incremental doses of midazolam administered by an operatorsedationist. The safety of this regimen has been questioned in a variety of clinical situations [1][2][3][4], and an alternative propofol-based sedation system has been developed recently [5][6][7][8]. The majority of targetcontrolled propofol infusion systems in clinical use are plasma level controlled. It is known that the clinical effect of propofol lags behind changes in its plasma concentration, which reflects the time taken for propofol to move from the plasma compartment to its site of action for sedation or hypnosis in the brain. It is assumed that when the clinical effect of propofol has reached a plateau, the plasma and brain concentrations have equilibrated. The effect-site concentration is a mathematically derived term that corresponds with the clinical effect of propofol [9]. Patient-maintained sedation (PMS) involves the patient controlling a target-controlled infusion of propofol by operating a patient-controlled handset, and has been assessed in a number of surgical models [5][6][7][8]. This has recently been changed from controlling the target plasma concentration of propofol, to controlling the effect-site concentration (C e ) [10].Ultimately, it is hoped that the system will be safe for use in the absence of an anaesthetist. However, in the previous pilot studies the patients retained the use of the handset throughout the procedure and were able to

SummaryIncreasing the calculated plasma concentration of propofol has been shown to increase choice reaction time and visual and auditory response times. We studied the relationship of reaction to a vibrating handset as the effect-site targetcontrolled propofol concentration was incrementally increased in 20 patients during sedation, before induction of general anaesthesia. The reaction time increased, initially slowly and then more rapidly, as the calculated effect-site concentration of propofol increased, until the reaction to the vibrating handset was lost at a mean (SD) propofol effect-site concentration of 2.0 (0.6) lg.ml )1 . The loss of response to verbal contact occurred at a propofol effect-site concentration of 2.4 (0.5) lg.ml )1 . Reaction time may be of use clinically to warn of impending loss of verbal contact. Patient-maintained sedation with propofol allows the patient to control a target-controlled infusion of propofol, and hence his ⁄ her level of sedation, using a handheld demand button. We previously found this technique to be safe and effective in patients having oral surgery and it allowed more rapid titration of, and recovery from, sedation when compared with operatoradministered midazolam [1][2][3]. In volunteer studies, however, some subjects were able to reach potentially unsafe levels of sedation (minor arterial oxygen desaturation or loss of verbal contact) when deliberately attempting to over-sedate themselves. This was despite altering the lockout time on a plasma concentrationdriven patient-maintained sedation system [4,5], or delivering propofol using a target effect-site (brain) concentration-driven system [6]. In that study, some volunteers were able to press the drug demand button successfully despite being over-sedated, suggesting that the inability to do so cannot be relied upon to prevent over-sedation.Previous studies have shown that choice reaction time and visual and auditory response times all increase as the calculated plasma concentration of propofol increases [7][8][9][10]. The aim of this study was to examine the effect of incrementally increasing the calculated effect-site concentration of propofol on the patient's reaction time, particularly as the patient approaches loss of verbal contact and hence over-sedation. The primary objective of this study was to characterise the relationship between the predicted effect-site concentration of

This case is presented to illustrate two clinical points. The first point is the diverse manner in which delirium can present, especially in the medically ill population, particularly the ability to present with signs and symptoms of anxiety and depression either as a prodrome or in the ‘body’ of the presentation. The second point relates to the use of ketamine. While its role as an analgesic is yet to be definitively outlined in palliative care, its neuropsychiatric side effects are better described. This report reviews ketamine's potential uses and provides a cautionary tale.