Statistical analysis
NRS
To determine the sample size needed for our study, we used PASS V.11.0 (PASS, NCSS, USA). Our primary focus was on measuring the duration of analgesia. In our pre-trial study of twelve patients (three in each group), the mean duration of analgesia in R, R + DXM, R + DEX and R + DXM + DEX group were 663 ± 261 min, 636 ± 373 min, 1120 ± 330 min and 880 ± 302 min, respectively. At a power of 0.80 and an alpha error of 0.05, the required sample size for each group was calculated to be 15. Considering the dropouts and incomplete follow-up, 18 patients per group and a total of 72 patients were suggested for this study.Statistical analysis was performed with SPSS V.19.0 for Windows. The distribution of the data was first evaluated for normality using the Kolmogorov–Smirnov test. Normally distributed continuous variables are expressed as the means ± standard deviation (SD). For duration of analgesia, total postoperative hydromorphone hydrochloride consumption and NRS data, ANOVA followed by the Bonferroni post hoc test was used. Categorical data (the incidence of side effects) were presented as frequencies (%) and analyzed using Fisher’s exact test. 