1.5 Statistical analysis
Statistical analysis was performed using SPSS22 for windows. Quantitative variables are presented as mean ± standard deviation when normally distributed, or as median (interquartile range, IQR) if non-normally distributed. Independent t-test and chi-square test were used to compare baseline characteristics between groups. We used univariate analysis and multivariable logistic regression to evaluate the risk factors with non-survivors. P < 0.05 were considered statistically significant.