Statistical Analysis
Continuous study data were presented as the mean ± Standard deviation. Categorical variables were pre­sented as the number and percentage. To compare the severity of each symptom between the groups with respect to continuous variables was tested with Student’s t-test or Mann-Whitney U test, with the former being used for normally distributed variables and the latter for non-normally dis­tribute dones. The difference with regard to categorical variables was tested using the chi-squared test. To determine potential risk factors for preoperative mortality, multivariable logistic regression analysis was performed. All statistical analyses were performed using SPSS package for Windows version 21 (SPSS Inc., Chicago, IL, USA). For all statistical analyses, p-value of <0.05 was considered statistically significant.