Statistical analysis
nausea
The sample size was calculated according to the incidence of nausea within 24 h after surgery in 20 patients before this experiment (the OFA group: 5%; the control group: 40%). The power analysis results of PASS software (90% power and a 5% significant level) suggested that each group should incorporate 31 patients. Considering the twenty percent dropouts, a total of 75 patients were included in the two groups in this study.Categorical variables were reported as number of cases (proportion) and analyzed using the Chi-square test or Fisher's exact test. Continuous variables were expressed as mean ± standard deviation or median (interquartile range). Normally distributed variables were analyzed using the Student's 