Peripheral oxygen saturation to inspiratory oxygen fraction ratio-based identification of critically ill coronavirus disease patients for early therapeutic interventions

BACKGROUND: Early identification of critically ill coronavirus disease (COVID-19) patients in clinical settings is crucial in reducing the mortality rate. Therefore, this study aimed to determine whether the saturation of peripheral oxygen (SpO(2)) to fraction of inspiratory oxygen (FiO(2)) ratio (SF ratio) at admission is useful for the early identification of severe COVID-19. METHODS: This single-center, retrospective, observational study conducted at the University Hospital, Kyoto, Japan, included 26 patients diagnosed with COVID-19 between January 24 and May 6, 2020. COVID-19 severity was classified into two groups based on the SF ratio: ≤ 235 (moderate to severe disease: low group) and > 235 (normal to mild disease: high group). The characteristics, laboratory data, and outcomes of the patients were examined retrospectively and compared between the groups. RESULTS: Of the 26 patients [median age 51.5 years, interquartile range 35.8–67.0], 6 were in the low group (23%) and 20 in the high group (77%). The low group had a higher respiratory rate than the high group (p < 0.05). Blood tests immediately after admission showed that the low group had significantly lower albumin (p < 0.01), and higher lactate dehydrogenase (p < 0.01), C-reactive protein (p < 0.01), and D-dimer (p < 0.01) levels than the high group. Moreover, all patients received antiviral agents; four received continuous renal replacement therapy and invasive positive pressure ventilation, one received extracorporeal membrane oxygenation, and two died in the low group. CONCLUSION: SF ratio measurement at admission could assist clinicians in the early identification of severe COVID-19, which in turn can lead to early therapeutic interventions.