Oxygenation indices and early prediction of outcome in hypoxemic patients with COVID-19 pneumonia requiring noninvasive respiratory support in pulmonary intermediate care unit

BackgroundEarly prediction of non-invasive respiratory therapy (NIRT) failure is crucial to avoid needless prolongation of respiratory support and delayed endotracheal intubation. Data comparing the predictive value of oxygenation indices (OI) in COVID-19 receiving NIRT are scant.The aim of this monocentric retrospective study of prospectively collected data was to assess the effectiveness of different OI in predicting NIRT outcome at baseline (t0), 12 h (t12) and 24 h (t24) of treatment in hypoxemic patients with COVID-19-related pneumonia, managed in a Pulmonary Intermediate Care Unit (October 2020-June 2021).BackgroundEarly prediction of non-invasive respiratory therapy (NIRT) failure is crucial to avoid needless prolongation of respiratory support and delayed endotracheal intubation. Data comparing the predictive value of oxygenation indices (OI) in COVID-19 receiving NIRT are scant.The aim of this monocentric retrospective study of prospectively collected data was to assess the effectiveness of different OI in predicting NIRT outcome at baseline (t0), 12 h (t12) and 24 h (t24) of treatment in hypoxemic patients with COVID-19-related pneumonia, managed in a Pulmonary Intermediate Care Unit (October 2020-June 2021).MethodsWe assessed the predictive value of SpO2/FiO2, PaO2/FiO2, standardised PaO2/FiO2 ratio (s-PaO2/FiO2), respiratory index (RI), arterial-alveolar oxygen gradient (a-ADO2), age adjusted arterial-alveolar oxygen ratio (adj-a-ADO2D). Receiver operating characteristics (ROC), AUC and best sensitivity-specificity cut-off values were calculated at t0, t12, t24. NIRT failure risk was adjusted for non-oxygenation predictors.ResultsAmong 590 patients with COVID-19 infection, 368 met the eligibility criteria for inclusion in the study [mean (CI95%): PaO2/FiO2 214(206,8-221,9); PaCO2 mean 32,9 mmHg,(32,4-33,4)]. NIRT failure and hospital mortality rate were 23,4% and 19,6%, respectively. Older age, male gender, agitation/confusion, need for sedation, inability to tolerate prone positioning were independent predictors of NIRT failure. SpO2/FiO2, a-ADO2 and adj-aADO2 at t12 and t24, PaO2/FiO2 and RI at t24 were associated with NIRT failure. Prognostic predictivity of OI increased from t0 to t24. Greater ROC-AUC values were obtained with SpO2/FiO2 0,662 (0,60-0,72) (t0), PaO2/FiO2 0,697 (0,63-0,76) (t12) and s-PaO2/FiO2 0,769 (0,71-0,83) (t24). NIRT failure was independently predicted by PaO2/FiO2, s-PaO2/FiO2 and RI at any observation time and by SpO2/FiO2 and O2 gradients respectively at t0 and t24. SaO2/FiO2 <= 300 (t0), PaO2/FiO2 <= 151,7 (t12) and s-PaO2/FiO2 <= 160,4 (t24) turned out to be the best predictors of NIRT outcome.ConclusionsOI showed different effectiveness in predicting NIRT failure within 24 h of treatment in COVID-19 related pneumonia. This may be due to the multi-factorial pathophysiology of hypoxemia. Our study empathises furthermore the role of non-oxygenation-related parameters in contributing to the outcome. These findings may be useful to build a predictive model also in no COVID-19 related hypoxemic pneumonia.