Assessment of the SpO2/FiO2 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 (SpO2/FiO2) to predict the ratio of partial pressure arterial oxygen to the fraction of inspired oxygen (PaO2/FiO2) 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 SpO2 and arterial blood gas. We compared SpO2 with SaO2 and evaluated performance of the SpO2/FiO2 ratio for the prediction of 300 and 400 mmHg PaO2/FiO2 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 SpO2/FiO2 ratio was 0.918 (CI 95% 0.885-0.950) and 0.901 (CI 95% 0.872-0.930) for PaO2/FiO2 thresholds of 300 and 400 mmHg, respectively. The positive predictive value (PPV) of an SpO2/FiO2 threshold of 350 for PaO2/FiO2 inferior to 300 mmHg was 0.88 (CI95% 0.84-0.91), whereas the negative predictive value (NPV) of the SpO2/FiO2 threshold of 470 for PaO2/FiO2 inferior to 400 mmHg was 0.89 (CI95% 0.75-0.96). No significant differences were found between the subgroups. CONCLUSIONS: The SpO2/FiO2 ratio may be a reliable tool for hypoxemia screening among patients admitted to the ED, particularly during the SARS-CoV-2 outbreak.

Authors' response: Novel criteria for dyspnea patients

Dear Editor, We would like to thank the authors of the recent letter “Novel Criteria for Dyspnea Patients” for sharing their concerns after reading our manuscript. In this study, we discussed the possibility of improving early patient assessment and identifying the presence of significant hypoxemia by using the SpO2/FiO2 ratio for all patients admitted for respiratory symptoms. Patients characteristics N = 395 Age, median (IQR) 60 (44–78) Gender, male, N (%) 193 (48.9%) Comorbidities Cardiac, N (%) 91 (23.0%) Heart failure, N (%) 71 (18.0%) Atrial fibrillation, N (%) 40 (10.1%) Coronary artery disease, N (%) 30 (7.6%) Other cardiac disease, N (%) 33 (8.4%) Pulmonary, N (%) 118 (29.9%) Asthma, N (%) 48 (12.2%) Chronic obstructive pulmonary disease(COPD), N (%) 51 (12.9%) Lung carcinosis, N (%) 10 (2.53%) Restrictive lung disease, N (%) 16 (4.05%) Other, N (%) 10 (2.53%) Acute kidney failure, N (%) 33 (8.4%) Chronic kidney disease, N (%) 29 (7.34%) COVID-19 status Positive, N (%) 90 (22.8%) Negative, N (%) 305 (77.2%) Diagnosis at discharge Pulmonary disease, N (%) 291 (73.7%) SARS-CoV-2, N (%) 90 (22.8%) COPD exacerbation, N (%) 21 (5.32%) Acute asthma, N (%) 18 (4.56%) Pneumonia, N (%) 49 (12.4%) Cardiogenic pulmonary oedema, N (%) 21 (5.32%) Respiratory acute viral syndrome (undetermined), N (%) 72 (18.3%) Others, N (%) 20 (5.06%) Extra-respiratory disease, N (%) 104 (26.3%) Vital signs Heart rate, median (IQR) 88 (77–101) Systolic blood pressure, median (IQR) 129 (115–144) Diastolic blood pressure, median (IQR) 77 (68–87) SpO2, median (IQR) 97 (95–99) Ventilatory rate, median (IQR) 22 (18–28) Temperature (°C), median (IQR) 37 (36.6–37.5) Blood gas analysis N = 430 Sample from COVID-19 patient, N (%) 94 (21.9%) FiO2 (%), median (IQR) 21 (21–29) PaO2 (mm Hg), median (IQR) 83.3 (71.3–97.5) SaO2 (%), median (IQR) 97.9 (96.4–98.9) PaCO2 (mm Hg), median (IQR) 36.0 (32.3–40.5) pH, median (IQR) 7.44 (7.41–7.47) PaO2/FiO2 (mm Hg), median (IQR) 364.3 (269.5–450) PaO2/FiO2 > 400, N (%) 164 (38.1%) PaO2/FiO2 300–400, N (%) 132 (30.7%) PaO2/FiO2 < 300, N (%) 134 (31.2%) SaO2/FiO2, median (IQR) 461.2 (339.0–470.5) SpO2/FiO2, median (IQR) 452.4 (337.9–466.7) Table 1 Characteristics of study subjects and samples.