Assessment of the SpO(2)/FiO(2) ratio as a tool for hypoxemia screening in the emergency department

OBJECTIVE: We assessed the performance of the ratio of peripheral arterial oxygen saturation to the inspired fraction of oxygen (SpO(2)/FiO(2)) to predict the ratio of partial pressure arterial oxygen to the fraction of inspired oxygen (PaO(2)/FiO(2)) among patients admitted to our emergency department (ED) during the SARS-CoV-2 outbreak. METHODS: We retrospectively studied patients admitted to an academic-level ED in France who were undergoing a joint measurement of SpO(2) and arterial blood gas. We compared SpO(2) with SaO(2) and evaluated performance of the SpO(2)/FiO(2) ratio for the prediction of 300 and 400 mmHg PaO(2)/FiO(2) cut-off values in COVID-19 positive and negative subgroups using receiver-operating characteristic (ROC) curves. RESULTS: During the study period from February to April 2020, a total of 430 arterial samples were analyzed and collected from 395 patients. The area under the ROC curves of the SpO(2)/FiO(2) ratio was 0.918 (CI 95% 0.885–0.950) and 0.901 (CI 95% 0.872–0.930) for PaO(2)/FiO(2) thresholds of 300 and 400 mmHg, respectively. The positive predictive value (PPV) of an SpO(2)/FiO(2) threshold of 350 for PaO(2)/FiO(2) inferior to 300 mmHg was 0.88 (CI95% 0.84–0.91), whereas the negative predictive value (NPV) of the SpO(2)/FiO(2) threshold of 470 for PaO(2)/FiO(2) inferior to 400 mmHg was 0.89 (CI95% 0.75–0.96). No significant differences were found between the subgroups. CONCLUSIONS: The SpO(2)/FiO(2) ratio may be a reliable tool for hypoxemia screening among patients admitted to the ED, particularly during the SARS-CoV-2 outbreak.