RT Journal Article SR Electronic T1 Response to the letter from Dr Yifeng Ren et al JF Regional Anesthesia & Pain Medicine JO Reg Anesth Pain Med FD BMJ Publishing Group Ltd SP rapm-2019-101021 DO 10.1136/rapm-2019-101021 A1 Zhu, Change A1 Zhang, Saiji YR 2019 UL http://rapm.bmj.com/content/early/2019/12/04/rapm-2019-101021.abstract AB