• Irene Prediletto, Letizia D'Antoni, Paolo Carbonara, Federico Daniele, Roberto Dongilli, Roberto Flore, PacilliAngela Maria GraziaAMGIRCCS Azienda Ospedaliero Universitaria di Bologna, University Hospital Sant'Orsola-Malpighi - Respiratory and Critical Care Unit - Bologna, Italy; Alma Mater Studiorum University of Bologna, Department of Clinical, Integrated, Lara Pisani, Corina Tomsa, María Laura Vega, Vito Marco Ranieri, Stefano Nava, and Paolo Palange.
• IRCCS Azienda Ospedaliero Universitaria di Bologna, University Hospital Sant'Orsola-Malpighi - Respiratory and Critical Care Unit - Bologna, Italy; Alma Mater Studiorum University of Bologna, Department of Clinical, Integrated and Experimental Medicine (DIMES), Bologna, Italy.
• Eur. J. Intern. Med. 2021 Oct 1; 92: 48-54.

IntroductionUp to fifteen percent of patients with novel pandemic coronavirus disease (Covid-19) have acute respiratory failure (ARF). Ratio between arterial partial pressure of oxygen (PaO2) and fraction of inspired oxygen (FiO2), P/F, is currently used as a marker of ARF severity in Covid-19. P/F does not reflect the respiratory efforts made by patients to maintain arterial blood oxygenation, such as tachypnea and hyperpnea, leading to hypocapnia. Standard PaO2, the value of PaO2 adjusted for arterial partial pressure of carbon dioxide (PaCO2) of the subject, better reflects the pathophysiology of hypoxemic ARF. We hypothesized that the ratio between standard PaO2 over FiO2 (STP/F) better predicts Covid-19 ARF severity compared to P/F.MethodsAim of this pilot prospectic observational study was to observe differences between STP/F and P/F in predicting outcome failure, defined as need of invasive mechanical ventilation and/or deaths in Covid-19 ARF. Accuracy was calculated using Receiver Operating Characteristics (ROC) analysis and areas under the ROC curve (AUROC) were compared.Results349 consecutive subjects admitted to our respiratory wards due to Covid-19 ARF were enrolled. STP/F was accurate to predict mortality and superior to P/F with, respectively, AUROC 0.710 versus 0.688, p = 0.012.Both STP/F and PF were accurate to predict outcome failure (AUROC respectively of 0.747 and 0.742, p = 0.590).DiscussionThis is the first study assessing the role of STP/F in describing severity of ARF in Covid-19. According to results, STP/F is accurate and superior to P/F in predicting in-hospital mortality.Copyright © 2021. Published by Elsevier B.V.

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