1 Department of Anesthesiology, West China Hospital of Sichuan University, Chengdu, Sichuan, China.
2 Department of Anesthesiology, West China Hospital of Sichuan University, Chengdu, Sichuan, China; Department of Anesthesiology, West China Tianfu Hospital of Sichuan University, Chengdu, Sichuan, China. Electronic address: wr.zhou@hotmail.com.