Sample size and statistical analysis
Based on our pilot study, whose protocol was the same as the formal study, FT3 in the S group at 1 h after the beginning of the operation was 0.32±0.28 and that in the P group was 0.15±0.14. Thus, the sample size was calculated with a power of 0.9 and alpha error of 0.05. At least 27.2 subjects per group were needed. Assuming a 10% dropout rate and to increase the credibility of this study, 64 patients were recruited (32 subjects for each group).All statistical analyses were performed with IBM SPSS Statistics V.21.0 (IBM Corp. Beijing, China). Continuous numerical variables were expressed as the mean±standard deviation (SD), and non-normal variables were also reported as the median (range) in addition to the mean±SD. The normality of these variables was assessed with the Shapiro-Wilk test and histogram. Homogeneity of variance was evaluated by Levene’s test, and the means of continuous variables were compared via independent 