2.4. Statistical analysis
obese
OBESE, COMPLICATIONS
The sample size was calculate using PASS v15 software. Based on our pilot study in obese patients, the first-attempt success rates with the ultrasound-assisted and landmark-guided were 81% and 53%, respectively. According to the calculation, 50 patients were required for each group at the 0.05 significance level (α = 0.05) and 90% power (β = 0.1). Considering possible dropouts, we increased the sample size to 59 patients per group. All data were performed using SPSS 25.0 or GraphPad Prism 8.0. Categorical variables such as the success rate of first attempt, anesthesia characteristics and complications of CSEA, were described as number and percentage, compared using the χ