Assessment of the SpO2/FiO2 ratio as a tool for hypoxemia screening in the emergency department

Abstract : 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 cutoff 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.