Statistical analysis
A pilot observational study in our center showed that the FLACC scores between the oxycodone and tramadol groups in PACU were 3.71 ± 1.71 and 4.49 ± 1.74, respectively. The sample size required was 166 patients (83 patients in each group) after calculation with two-tailed α = 0.05 and β = 0.2 using the SAS software (SAS Institute Inc., USA). Considering the possible dropout cases, we increased the sample size to 240 for initial enrollment.GraphPad Prism 6.0 software (GraphPad Software Inc., USA) was used to perform the statistical analysis. The per-protocol analysis set consists of subjects who were randomly assigned to treatment, and have no major protocol violations such as violations of entry criteria, errors in treatment assignment and use of excluded medications. Gaussian distribution was tested using D’Agostino & Pearson analysis. Data was displayed as the median value (1st -3rd quartiles). An unpaired t test (if the data was normally distributed) or Mann-Whitney u test (if the data was not normally distributed) was used to analyze the numeric variables. FLACC scores, Ramsay sedation scores, and parent satisfaction scores were analyzed using a linear mixed-model to analyze the interaction and main effects of time and group. χ2 test or Fisher exact probability method (if the theoretical frequency was less than 5) was used to analyze the categorical variables were analyzed. A significant difference was defined as a value of P < 0.05.