Choosing optimal outcome measures maximizes statistical power, accelerates discovery and improves reliability in early-phase trials. We devised and evaluated a modification to a pragmatic measure of oxygenation function, the 𝑆/𝐹 ratio.
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 (π‘ƒπ‘Žπ‘‚2/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.


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Cite as

Swets, M., Kerr, S., Scott-Brown, J., Brown, A., Gupta, R., Millar, J., Spata, E., McCurrach, F., Bretherick, A., Docherty, A., Harrison, D., Rowan, K., Young, N., Groeneveld, G., Dunning, J., Nguyen-Van-Tam, J., Openshaw, P., Horby, P., Harrison, E., Staplin, N., Semple, M., Lone, N. & Baillie, J. 2023, 'Evaluation of pragmatic oxygenation measurement as a proxy for Covid-19 severity', Nature Communications, 14, article no: 7374. https://doi.org/10.1038/s41467-023-42205-6

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Last updated: 01 December 2023
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