Statistical analysis
ASD
Analyses were performed using IBM SPSS Statistics for Windows version 22.0 (IBM Corp, Armonk, NY, USA), GraphPad Prism version 5.0 (GraphPad Software Inc., San Diego, CA, USA), and Microsoft Excel (Microsoft Corporation, Redmond, WA, USA). We assessed the distribution of the continuous variables using graphical displays of the data and the Kolmogorov-Smirnov test. Demographic data characteristics were presented using descriptive statistics. To evaluate baseline imbalance in the randomization of the four infusion doses, the absolute standardized difference (ASD) between each pair among the four infusion doses were calculated for each parameter. The maximum ASD among all pairs was identified. Imbalance was estimated as the maximum ASD being greater than the value calculated by the following equation (based on the recommendation for small sample sizes by Austin [For normally distributed data (including demographic data), the volume of i.v. crystalloid and umbilical arterial pH values were presented as the mean and standard deviation (SD). One-way analysis of variance (ANOVA) was used to assess whether all the means were identical. Then, 