Sample size calculation
To calculate the sample size, a pilot study was performed to evaluate the time to adequate analgesia (VAS ≤ 3) in 10 patients, with 5 patients receiving normal saline intranasally (CON) and 5 receiving 0.5 μg/kg dexmedetomidine hydrochloride intranasally (IND) 15 min before the epidural procedure. The median onset time of the CON group was 10.2 min, while that of the IND group was 7.9 min. The standard deviations (SDs) were 2.1 and 2.6, respectively. For a power of 90% and two-sided statistical significance set at 0.05, the minimum sample size was calculated by PASS15.0 software to be 24 patients per group [