2.11.1. 118 cases (59 cases per group).
The sample size was calculated using the total dose unit (1 unit 17.5 mg) of the concomitant analgesic pethidine hydrochloride, which is the primary endpoint of this study. From an exploratory study conducted in advance, the average total dose of pethidine hydrochloride in the NHF-using group and the low flow oxygen group was 2.774 units and 3.933 units, respectively.