Randomization and blinding
pain
BLIND
The patients were allocated randomly to the OFA group or the control group according to a computer-generated random number table. Allocation to the treatment group was performed using the sealed opaque envelope technique. Sealed envelopes were marked as the OFA group or the control group and were opened only when the patient entered the operating room. The patient, outcome assessor, and nurses in the postanesthetic care unit (PACU) and surgical ward were blinded to the grouping. Due to the significant differences in anesthesia methods, anesthesiologists knew the allocation of patients. Before surgery, patients were instructed to complete pain scoring on the VAS rating scale. 0 points represented no pain, and 10 points represented the most severe pain. All operations were performed with a standardized technique. An investigator who was blind to the grouping was trained to interview patients and fill in the quality of recovery 40 questionnaires (QoR-40) [