Statistical analysis
SD
The sample size was based on a pilot study involving 30 patients who were excluded from the main study. In the pilot study, morphine consumptions (mean ± standard deviation [SD]) in the magnesium sulfate and control groups on postoperative day 1 were 6.7 ± 5.8 mg and 11.6 ± 7.5 mg, respectively. We computed the smallest sample size of 39 patients in both groups with a bilateral alpha level of 0.05 and power of 90%. Considering the risk of dropout, 45 patients were included in each group.The Shapiro–Wilk test was used to evaluate data normality. Continuous and categorical data are expressed as mean ± SD together with percentage or number, respectively. The Student All statistical analyses were performed using SPSS version 25 (IBM Corp, Armonk, NY, USA). Differences were considered significant if 