Randomization and blinding
The investigators used the SAS statistical software package on a computer to generate random numbers in a 1:1 ratio to determine groups S and C. Neither the blinded investigators (the surgeon and the anesthesia resident physician) nor the patients were aware of the study groupings. Before the patients entered the operating room, the attending anesthetist opened the envelope, and the patients were assigned to group S or C according to the randomization entry number. Another anesthetist resident physician did not know the group assignment, and performed the subsequent anesthesia and the postoperative follow-up. A CONSORT diagram shows the participant flow (Flow chart of participants.