Statistical analysis
The sample size calculation was based on the primary outcome of haemodynamic changes in elderly patients during operation and calculated using the PASS 15 software. According to a previous study about the decrease of heart rates after dexmedetomidine infusion in elderly patients with hip replacement under general anaesthesia [Statistical description and analysis of collected data were performed with SPSS version 22.0 (IBM Corp.). All tests were two-tailed, and 