Authors’ contributions
Study design and supervision: Qianzi Yang and Hailong Dong. Project administration and randomization: Ao Li, Tingting Liu, Xue Yang. Generating the random allocation sequence: Ao Li. Preparing s-ketamine or saline: Huanhuan Zhang. Data collection: Tiantian Liu. Anesthesiologist: Yanling Lei. Data analysis: Tiantian Liu, Xinxin Zhang and Ao Li. Figures 