Standardizing PaO2 for PaCO2 in P/F ratio predicts in-hospital mortality in acute respiratory failure due to Covid-19: A pilot prospective study

Abstract

Up to fifteen percent of patients with novel pandemic coronavirus disease 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. Methods: Aim 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. Results: 349 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).

Single-Breath Counting Test Predicts Non-Invasive Respiratory Support Requirements in Patients with COVID-19 Pneumonia

“…Our data confirms preceding studies which showed that in patients with COVID-19 pneumonia low P/F, low SpO 2 /FiO 2 ratio, low PCO 2 and the presence of dyspnea at rest predict the need of NIRS [ 12 , 13 , 14 , 34 , 35 ]. Of note, there is a slight discrepancy between PaO 2 /FiO 2 and SpO 2 /FiO 2 cut off, which predicts NIRS requirement (respectively 280 and 438).…”

Early Variation of Respiratory Indexes to Predict Death or ICU Admission in Severe Acute Respiratory Syndrome Coronavirus-2-Related Respiratory Failure

“…A correction of PaO2 by arterial carbon dioxide tension (PaCO2) − namely, standardized PaO 2 − was suggested to overcome this latter limit [ 10 ]. The role of standard P/F ( ST P/F) ratio was recently found to be accurate and superior to P/F in predicting in-hospital mortality in coronavirus disease 2019 (COVID-19) [ 11 ].…”

Patient self-induced lung injury risk in severe COVID-19

“…Unfortunately, we did not record PaCO 2 values during our two studies [2] , [4] ; however, previous literature showed that patients with severe COVID-19 have lower inspiratory effort in comparison to matched non-COVID-19 cohort with respiratory failure, suggesting lower risk of P-SILI in patients with COVID-19 [4] . Furthermore, data from COVID-19 patients showed that PaCO 2 was not significantly lower in patients who later needed mechanical ventilation, and that PaCO 2 showed low accuracy in predicting the need for mechanical ventilation and/or death with area under receiver operating characteristic (95% confidence interval) of 0.57 (0.51 to 0.68) [5] . Thus, we suggest that the level of PaCO 2 on hospital admission is unlikely a predictor of severity of the disease.…”