SpO2/FiO2 Correlates with PaO2/FiO2 (P/F) and Radiological Biomarkers of Severity: A Retrospective Study on COVID-19 Pneumonia Patients

Background: In patients with COVID-19 pneumonia, the estimation of PaO2 represents the method of choice for monitoring a patient’s oxygenation status and assessing disease severity. The aim of this study is, therefore, to investigate the correlation between SpO2/FiO2 and PaO2/FiO2, as well as radiological and laboratory biomarkers of severity. Methods: In this monocentric observational, analytical, retrospective large cohort study, consecutive patients with a confirmed diagnosis of pneumonia from SARS-CoV-2, hospitalized at the Cotugno Hospital—AORN dei Colli—of Naples, between 1 September 2020 and 28 February 2022 were considered for study inclusion. Patients with missing data were excluded. Results: We included 585 patients (median age 63 [22–95]). Mean PaO2/FiO2 was 203 [66–433], whilst mean SpO2/FiO2 was 240 [81–471]. We found that P/F ratio could be predicted from S/F ratio, as described by the linear regression equation (P/F = 13.273 + 0.790 × S/F). In addition, we found that SpO2/FiO2 ratio significantly correlated with HRCT score and laboratory markers of severity, including IL-6, D-Dimer, and NLR. Conclusions: SpO2/FiO2 ratio represents a highly useful resource as a valid surrogate of P/F ratio in patients with COVID pneumonia, also correlating with other biomarkers of severity, such as HRCT score and key laboratory markers.