 One anaesthetist will look after the air way while the second anesthetist or a research assistant will fill in the data collection sheet and determine point of loss of consciousness and point of loss of response to painful stimuli. The air way anesthetist will know by a sealed envelope whether the patient is on group A or B. For the patients in group A, the remifentanil infusion, using the minto effect site concentration model, will be set at 0ngml. For the patients in group B the remifentanil infusion will be set at 3ngml. After 5 minutes the propofol infusion will commence, using the Marsh effect site concerntration TCI model, at 1mcgml and will be increased by 0.2mcgml every one minute. Heart Rate, blood pressure and BIS number will be recorded every minute. Every 30 seconds the anaesthetist will prompt the patient with the vocal stimuli say your name in a constant tone and volume. Loss of consciousness will be defined as the point at which the patient fails to respond to the vocal stimuli and light tactite stilulation. At this point BIS, heart rate, blood pressure and propofol effect site concentration will be recorded. 