Introduction: Moderate COVID-19 comprises majority of cases reported in terms of severity. Prediction of deterioration among these should be prioritized. To date, there are no definitive recommendations on inclusion of specific oxygenation parameters such as Arterial Alveolar Oxygen Ratio (aAO2), Alveolar-arterial Oxygen Difference (AaDO2) and Arterial Oxygen Tension Fraction Inspired Oxygen ratio (PF ratio) in initial management of these cases. We aimed to evaluate the association of AaDO2, aAO2, and PF ratio with mortality and initiation of oxygen therapy among moderate COVID-19 patients.

Methods: 305 admitted moderate COVID-19 adults were included. Baseline profiles were reviewed. The admission arterial blood gas on room air was recorded and oxygenation parameters were calculated. The occurrence of clinical outcomes was reviewed. ROC curves were generated, followed by the derivation of cutoff values, simple logistic regression analysis, and determination of sensitivity(Sn) and specificity(Sp).

Results: There was a significant association in terms of initiation of oxygen therapy. With high Sn and Sp, those with aAO2, AaDO2, and PF ratio cut-offs of <0.71 (Sn88.82, Sp90.20), >31.86 (Sn90.82, Sp93.46) and <366.67 (Sn85.57, Sp83.01) respectively were likely to be initiated on oxygen therapy. In terms of initiation of high flow oxygen therapy, there was noted association, however with lower Sn and Sp. In terms of mortality, there was no significant association.

Conclusion: AaO2, AaDO2 and PF ratio may be effective tools to predict initiation of oxygen therapy, among adults with moderate COVID-19 infection. Integration in COVID-19 management may be highly considered.