M H M Chu1, S Tsang2, W K K Wu2, M Chan3. 1. Department of Anaesthesia, Pamela Youde Nethersole Eastern Hospital, Chai Wan, Hong Kong Special Administrative Region, China. 2. Department of Anaesthesia and Intensive Care, The Chinese University of Hong Kong, Prince of Wales Hospital, Shatin, New Territories, Hong Kong Special Administrative Region, China. 3. Department of Anaesthesia and Intensive Care, Prince of Wales Hospital, Shatin, Hong Kong.