Randomization and blinding
All patients were randomly divided into OFA group (Group OFA) or OA group (Group OA). Randomization was conducted using a computer-generated allocation sequence with a 1:1 allocation by an independent investigator. The randomization sequence was placed in sequentially numbered opaque sealed envelopes and revealed by another investigator after the participants’ enrollment, followed by preparing the study drugs wrapped with opaque paper according to the allocated group and delivered them to the operating room. The result of the group allocation was not released until the time of data analysis. Anesthesia was conducted by an experienced anesthesiologist and the outcome assessments were carried out by another one. Participants, anesthesia implementers and outcome assessors were untold of the group allocation.