Correlation of SpO₂/FiO₂ and PaO₂/FiO₂ in patients with symptomatic COVID-19: An observational, retrospective study

Some patients affected by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) experience acute hypoxemic respiratory failure progressing toward atypical acute respiratory distress syndrome (ARDS). The aim of the study is to evaluate whether a correlation between ratio of peripheral saturation of oxygen (SpO₂) and fraction of inspired oxygen (S/F) and ratio of arterial partial pressure of oxygen and fraction of inspired oxygen (P/F) exists in COVID-19-related ARDS as already known in classical ARDS. In this multicenter, retrospective, observational study, consecutive, adult (≥ 18 years) patients with symptomatic coronavirus disease 2019 (COVID-19) admitted to different COVID-19 divisions in Italy between March and December 2020 were included. Patients with SpO₂ > 97% or missing information were excluded. We included 1,028 patients (median age 72 years, prevalence of males [62.2%]). A positive correlation was found between P/F and S/F (r = 0.938, p < 0.0001). A receiver operating characteristic (ROC) curve analysis showed that S/F accurately recognizes the presence of ARDS (P/F ≤ 300 mmHg) in COVID-19 patients, with a cut-off of ≤ 433% showing good sensitivity and specificity. S/F was also tested against P/F values ≤ 200 and ≤ 100 mmHg (suggestive for moderate and severe ARDS, respectively), the latter showing great accuracy for S/F ≤ 178%. S/F was accurate in predicting ARDS for SpO₂ ≥ 92%. In conclusion, our findings support the routine use of S/F as a reliable surrogate of P/F in patients with COVID-19-related ARDS.