Alveolar-to-arterial oxygen gradient: role in the management of COVID-19 infection mild population

Abstract COVID-19 infection is frequently associated with radiological diagnosis of interstitial pneumonia and alteration in gases exchange. We decided to test arterial blood gas assay parameters, in particular alveolar-to-arterial oxygen gradient (AaDO2), in predicting the need of hospitalization, the survival rate and in identifying pneumonia in patients with SARS-CoV-2 infection.We conducted an observational prospective study in one of the Emergency Department of our city. We included consecutive patients with symptoms likely related to SARS-CoV-2 infection, confirmed either with positive nasal pharyngeal swabs and/or with suggestive radiological findings. Areas under the curve of the receiver operator characteristic curve were computed to predict need of hospitalization and the presence of pneumonia. Survival curves were analyzed using a Log-rank test. P-value less than 0.05 were considered statistically significant.We enrolled 825 patients; the final population was composed by 530 patients. Most of them were hospitalized due to complications, the mortality was 14% but no death occured in the ED. It results that a threshold for AaDO2 of 27 could predict the need of hospitalization as well as a threshold for AaDO2 of 24 could identify the presence of pneumonia. Survival curves revealed that patients with a value of AaDO2 less than or equal to 40 had a better survival. We suggest the application of ABG parameters, in particular AaDO2, during the first assessment of COVID-19 patients in the ED, because they could be additional tools to help the emergency physician to evaluate the clinical severity of patients.The study was approved by our local ethics committee with the number 551/2020/Oss/AOUBo.