Auditory recall and response to command during recovery from propofol anaesthesia

Most studies of awareness under general anaesthesia use the ability to respond to a verbal command as the primary measure of consciousness. The aim of this pilot study was to discover whether it was possible for subjects recovering from a propofol general anaesthetic to experience conscious awareness without the capability of responding to verbal command. Ten healthy volunteers received an intravenous propofol infusion (1500 mg/hr) until they were no longer conscious. The infusion was then stopped and they were given verbal commands interspersed with random numbers from a recorded tape until they were able to respond appropriately. Seven of the subjects were able to remember numbers corresponding to times 10 to 40 seconds before they responded to verbal command. In none of these subjects was there recall of the number 30 minutes later. We concluded that there is an ability to have conscious awareness of auditory input without necessarily being able to demonstrate this by responding to verbal command.