Safety of patient-maintained propofol sedation using a target-controlled system in healthy volunteers

We investigated the safety of a patient-maintained system that allows indiv iduals to operate a target-controlled infusion of propofol to achieve sedat ion. Ten healthy volunteers were recruited and instructed to try to anaesth etize themselves with the system. A target-controlled infusion of propofol was set to deliver a target propofol concentration of 1 mu g ml(-1), and th e subjects allowed to increase the target in increments of 0.2 mu g ml(-1) by pressing a control button twice in I a. There was a lockout time of 2 mi n and a maximum permitted target concentration of 3 mu g ml(-1). Heart rate and pulse oximetry oxygen saturation (Sp(O2)) were monitored continuously, and non-invasive arterial pressure, ventilatory frequencies and sedation s cores were measured every 5 min. Sedation was continued until the subject s topped pressing the button. A keyword was then read for the individual to r emember and sedation discontinued. There were no instances of significant d ecrease of Sp(O2) or loss of airway control. Maximum target blood concentra tion of propofol recorded ranged from 1.4 to 3 mu g ml(-1). Two subjects be came oversedated, one of whom was unrousable with loss of eyelash reflex. N o subject could recall the keyword, although one recognized it from a list of 10 words. We conclude that the patient-maintained sedation system descri bed could not be guaranteed to produce only conscious sedation in all patie nts, and that close clinical supervision by an anaesthetist would still be required for safe operation.