Sample size and statistical analysis
PONV
SPSS statistics 17.0.1 (SPSS, Inc., Chicago, Illinois) was used for statistical analysis. For data analysis, the normality test in SPSS statistical software was used to determine whether the data conformed to a normal distribution. Continuous variables with a normal distribution are expressed as the mean ± standard deviation and were analysed by Student’s t test. The Mann‒Whitney U test was used for continuous variables with a nonnormal distribution. Haemodynamic parameters were compared with repeated ANOVA measurements. Categorical variables are expressed as frequencies (percentages) and were analysed using the Pearson chi-square test. The Wilcoxon signed-rank test was used to compare continuous variables. A p value < 0.05 was considered statistically significant.Because the incidence of PONV caused by different risk factors varies, we assumed that the incidence rate of PONV would be decreased from 39 to 19% in this study. A sample size of 102 participants in each group was calculated, and the significance level was 0.05 (α = 0.05). Given a 10% attrition rate, the strength was 80% (β = 0.20) [