Statistical Analysis

Continuous data were expressed as mean ± standard deviation or median with interquartile range. Categorical data were presented as percent (count). CCI was transformed into binary variable, and the median of CCI (4) was set as the cutoff. Baseline characteristics between the PNB and SA groups were summarized and compared using bivariate tests (Mann–Whitney U, χ², and Fisher’s exact tests). Patient demographics and baseline clinical data that could possibly affect postoperative morbidity and mortality were included, and a PSM analysis was performed with a ratio of 1:1. The rationale and methods of PSM to evaluate cause-and-effect relationships in retrospective studies have been well described.¹⁹ Briefly, the propensity score was calculated by logistic regression analysis using patient demographics and baseline clinical data to examine the association of anesthesia type with 30-day, 90-day, and one-year mortality. The tolerance error of PSM was 0.02. One-year survival analysis was performed using Kaplan-Meier analysis with Log rank test. Two-tailed tests were used, and differences were considered significant if p<0.05. SPSS 20.0 statistical software (Chicago, IL, USA) was used for the analysis.