Statistical Analysis
Statistical analysis was performed with IBM SPSS 24.0 software. Statistical results are presented as median (Q1-Q3) or mean ± standard deviation. Baseline analysis among groups was performed with chi-square tests or Fisher’s exact tests for categorical data and the 2-tailed t test or the Mann–Whitney test for continuous data. Multivariable analysis was performed for variables that demonstrated statistical significance in the univariable analysis. Logistics regression was used for both univariate and multivariable analysis. Receiver operator characteristic curves (ROC curves) were used for the determination of the best cutoff point in predicting postoperative mortality. This cutoff point was determined by maximizing the Youden index (= sensitivity+specificity-1) of a ROC curve. Survival curves were plotted using the Kaplan-Meier method, and statistical differences were compared using a log-rank test. A P value less than 0.05 was considered statistically significant.