From the Department of Anesthesiology, Sichuan Provincial People's Hospital, University of Electronic Science and Technology of China, Chengdu, China (WC, YL) and Department of Anesthesia, The Sixth Affiliated Hospital, Sun Yat-sen University, Guangzhou, Guangdong, China (ZZ)

Correspondence to Yang Liu, Department of Anesthesiology, Sichuan Provincial People's Hospital, University of Electronic Science and Technology of China, 32# W. Sec 2, 1st Ring Road, Chengdu 610000, China. Tel: +86 028 87393999; e-mail: [email protected]

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