title: Letter to the editor.
authors.affiliation: Department of Anesthesiology, Affiliated Hospital of Qingdao University Medical College, Qingdao, People's Republic of China, Department of Anesthesiology, Nan Fang Hospital, South Medical University, Guangzhou, People's Republic of China.
authors.forename: Yong X
authors.initials: YX
authors.lastname: Liang
authors.affiliation: Department of Anesthesiology, Nan Fang Hospital, South Medical University, Guangzhou, People's Republic of China.
authors.forename: Miao N
authors.initials: MN
authors.lastname: Gu
authors.affiliation: Department of Anesthesiology, Affiliated Hospital of Qingdao University Medical College, Qingdao, People's Republic of China.
authors.forename: Shi D
authors.initials: SD
authors.lastname: Wang
authors.affiliation: Department of Anesthesiology, Affiliated Hospital of Qingdao University Medical College, Qingdao, People's Republic of China.
authors.forename: Xiang Y
authors.initials: XY
authors.lastname: Ji