163 S/F94 as a proxy for COVID-19 severity 7 oxygenation defects, and deteriorate rapidly, have a slightly increased risk of mortality. Sensitivity analyses We carried out a sensitivty analysis not including assigned minimum and maximum values for those who died or were discharged. The logistic regression analysis used to evaluate the association between 28-day mortality and S/F94 on day 5, corrected for S/F94 on day 0, showed an OR of 0.33. For a 1 unit increase in S/F94, the odds of 28-day mortality decrease by 66%. The mean of S/F94 decreased from 2.39 in the main analysis to 2.17 in this sensitivity analysis, which was due to the fact that Linear regression lines SaO2 < 1.00orFIO2 = 0.21 SaO2 < 0.98orFIO2 = 0.21 SaO2 < 0.96orFIO2 = 0.21 SaO2 < 0.94orFIO2 = 0.21 SaO2 < 0.92orFIO2 = 0.21 SaO2 < 0.90orFIO2 = 0.21 0 20 40 60 80 100 PaO2/FIO2 ratio (kPa) 0 1 2 3 4 5 SaO2/FIO2 ratio 0.5 0.6 0.7 0.8 0.9 1.0 SaO2 0 1 2 3 4 5 SaO2/FIO2 ratio 0 20 40 60 80 100 PaO2/FIO2 ratio (kPa) 0.5 0.6 0.7 0.8 0.9 1.0 SaO2 a b c Supplementary Figure 1. (a,b) Scatter plots showing real blood gas results from critically ill patients. S/F is plotted against our reference standard, P/F. Points are coloured according the SaO2 as shown in the colour scale. (a) including all values with no maximum SaO2. Linear regression lines are shown for S/F against P/F in using different maxima for SaO2; patients breathing air (FIO2=21%) were included in all regression analyses regardless of SaO2. (b) shows only values meeting the criteria for S/F94: SpO2 ≤ 0.94 or FIO2 = 21% (c) Optimisation of cut-off value for SaO2 using change in correlation coefficient (Spearman r) as the threshold for inclusion is lowered from SaO2<100% to SaO2<80%.
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