2.6. Sample size
Previously, we found that the average time to extubation at our institution was 17 ± 5 minutes in 37 patients who were > 75 years old and underwent spinal surgery under propofol-remifentanil anesthesia from April 2019 to March 2020 in Hiroshima University Hospital.The G*power 3.1.0 program (We used a type 1 error of α = 0.05, and a power of 0.80 to calculate sample sizes.Considering a dropout rate of 15 %, 22 patients per group were enrolled in this study.