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

Abstract

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.

Keywords: COVID-19; HRCT; SARS-CoV-2; SF ratio; SpO2/FiO2; laboratory biomarkers.

Figure 1

Correlation between S/F ratio and P/F ratio.

Figure 2

Receiver operator characteristic (ROC) curve analyses: (A) the predictive role of P/F ratio towards the HRCT score; (B) the predictive role of S/F ratio towards the HRCT score.

Figure 3

Box plots of mean serum concentrations of D-Dimer (A,D), IL-6 (B,E), and NLR value (C,F) based on SF (A–C) and PF (D–F) ratio, respectively. p < 0.001.