Estimated Sp02/Fio2 ratio to predict mortality in patients with suspected COVID-19 in the Emergency Department: a prospective cohort study

Background This study examined whether the presence and severity of Type 1 Respiratory Failure (T1RF), as measured by the ratio of pulse oximetry to estimated fraction of inspired oxygen (SpO2/eFiO2 ratio), is a predictor of in-hospital mortality in patients presenting to the ED with suspected COVID19 infection. Methods We undertook a prospective observational cohort study of patients admitted to hospital with suspected COVID-19 in a single ED in England. We used univariate and multiple logistic regression to examine whether the presence and severity of T1RF in the ED was independently associated with in-hospital mortality. Results 180 patients with suspected COVID19 infection met the inclusion criteria for this study, of which 39 (22%) died. Severity of T1RF was associated with increased mortality with odds ratios (OR) and 95% confidence intervals of 1.58 (0.49 to 5.14), 3.60 (1.23 to 10.6) and 18.5 (5.65 to 60.8) for mild, moderate and severe T1RF, respectively. After adjusting for age, gender, pre-existing cardiovascular disease, neutrophil-lymphocyte ration (NLR) and estimated glomerular filtration rate (eGFR), the association remained, with ORs of 0.63 (0.13 to 3.03), 3.95 (0.94 to 16.6) and 45.8 (7.25 to 290). The results were consistent across a number of sensitivity analyses. Conclusions Severity of T1RF in the ED is an important prognostic factor of mortality in patients admitted with suspected COVID19 infection. Current prediction models frequently do not include this factor and should be applied with caution. Further large scale research on predictors of mortality in COVID19 infection should include SpO2/eFiO2 ratios or a similar measure of respiratory dysfunction.