Randomization and masking
The study participants were randomly grouped on a scale of 1:1 using a computer-generated list of random numbers. The distribution results are sealed in an opaque envelope and kept by the study manager. On a surgical day, the study manager handed the envelope to the anesthesia assistant who dispensed the anesthetic fluid. The patients were randomly assigned to two groups: the saline placebo group and the lidocaine group, with 33 patients in each group.Drugs were prepared in 20 ml syringes (for bolus administration) and another 20 ml syringes (for continuous infusion), containing 2% lidocaine solution or an equal amount of 0.9% normal saline. Postoperative patient-controlled intravenous analgesia (PCIA) with sufentanil and with or without lidocaine. The assistant handed a syringe full of liquid medicine or PCIA to the anesthesiologist without knowing which patient was in which group. Thus, group assignments are blinded by patients, healthcare providers, and data collectors.