An intravenous cannula will be inserted then. The degree of the cannulation pain will be assessed as using NRSpaincannulation. The intravenous cannula is connected to a 50 mL syringe patient-controlled analgesia pump containing 200 mg (20 mL) propofol and 0.5 mg (1 mL) alfentanil, which will be provided as the rescue sedative medications. The drugs are delivered in response to pressure on a hand-held button. Each bolus dose of 0.5 mL delivered contained 4.8 mg propofol and 12 μg alfentanil. No loading dose was used and the lock out time was set at zero. Despite the zero lock out time, a few seconds were required for the pump to deliver the preset bolus. The PCA pump was programmed to deliver a bolus dose of 0.5 ml at 200 ml/h on patient's demand and the pump took 9 s to deliver the bolus, during which time it would not respond to a further demand. Thus, the effective lockout time was 9s. Patients are instructed in the use of the hand-held button before upper endoscopy.