2.2. Sample size calculation
The minimal sample size was calculated according to our unpublished preliminary study with 30 patients, which showed that the mean of mean arterial blood pressure (MAP) taken right before intubation was 79.2 (±10.1) in the esketamine group and 72.9 in the control group. We set α = 0.05, 1-β = 0.95, and used the “Sample Size Calculator” to calculate the sample size online