Randomisation and blinding
A total of 236 random numbers were generated by IBM SPSS Statistics 25 (IBM Corp. Released 2017. IBM SPSS Statistics for Windows, Version 25.0. IBM Corp, Armonk, NY, USA), and the software randomly divided the 236 numbers into four groups. Cases were enrolled according to the order of enrolment time corresponding to random numbers from small to large, and a random number corresponded to the admission ID number of the patient. A full-time anaesthesiologist (Investigator A) performed these assignments. The patient entered the operating room, and investigator A induced general anaesthesia according to the conventional method. Tracheal intubation was performed after smearing and/or spraying the tracheal tube according to the enrolment information. After completion of tracheal intubation, another anaesthesiologist (Investigator B) performed anaesthesia management according to conventional methods and collected data until the end of the study. All of the collected data were handed over to Investigator A for sorting into different groups, and Investigator C performed statistical analyses. The patients and Investigators B and C were all blinded to the grouping information.