For the primary outcome measure, mortality, we did
power calculations assuming a 12% absolute difference
in mortality between treatment arms, based on the
study by Denniston et al.16 We calculated that a total
of 200 participants (100 in each of two equal sized
groups) would provide 83% power to detect a 70%
reduction in mortality, from 14% in the high flow oxygen treatment arm to 2% in the titrated oxygen treatment arm. This sample size would also provide 94%
power to detect a difference in arterial carbon dioxide
pressure of 10 mm Hg (common SD 20 mm Hg)
between the two groups. We allowed for a 25% dropout rate and thus needed a minimum of 135 participants in each arm