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Abstract / Description of output
Because of the ceiling effect in oxyhaemoglobin saturation, 𝑆/𝐹 ratio ceases to reflect pulmonary oxygenation function at high 𝑆𝑝𝑂2 values. We found that the correlation of 𝑆/𝐹 with the reference standard (𝑃𝑎𝑂2/𝐹𝐼𝑂2 ratio) improves substantially when excluding 𝑆𝑝𝑂2 > 0.94 and refer to this measure as 𝑆/𝐹94.
Using observational data from 39,765 hospitalised COVID-19 patients, we demonstrate that 𝑆/𝐹94 isn predictive of mortality, and compare the sample sizes required for trials using four different outcome measures. We show that a significant difference in outcome could be detected with the smallest sample
size using 𝑆/𝐹94.
We demonstrate that 𝑆/𝐹94 is an effective intermediate outcome measure in COVID-19. It is a noninvasive measurement, representative of disease severity and provides greater statistical power.