Randomization and blinding
The simple randomization was chosen in our trial which was performed using an online randomization list to ensure that each group contained 22 subjects. The subjects were randomly assigned 1:1 to either the saline group or the s-ketamine group. The randomization envelopes contained grouping information. The nurses who preserved and opened the envelops and prepared the s-ketamine or 0.9% saline were not involved in patient care. S-ketamine was diluted in saline to a total volume of 10 ml. The same volume of saline was used in the control group. Syringes of saline and ketamine were identical. The other investigators and all subjects were blinded to randomization.