Oxygenation Index, Oxygen Saturation Index vs PaO₂/FiO₂ *PEEP: A Secondary Analysis of OXIVA-CARDS Study

The classification of Berlin definition is based on the PaO₂/FiO₂ ratio, which has been found to have a poor association with mortality. Airway pressures reflect lung compliance and the settings of mechanical ventilators. In this study, we aimed to investigate the change in the severity of COVID-19-associated acute respiratory distress syndrome (ARDS) classification using [PaO₂/FiO₂ × PEEP] (P/FP) ratio compared to the traditional P/F ratio, and whether the P/FP ratio improves the predictive validity of in-hospital mortality.

Our study sample included patients from the OXIVA-CARDS study. In this secondary analysis, we examined the oxygenation index and oxygen saturation index in relation to the P/FP ratio, as well as the risk of P/FP in mortality. We used Pearson's correlation to assess the relationships between various parameters. Receiver operating characteristic analysis with Youden's index was used to compare the prognostic value of the oxygenation index (OI), oxygen saturation index (OSI), P/F ratio, P/FP ratio, and SaO₂/FiO₂ ratio for predicting overall mortality. Multiple logistic regression was also performed to determine the impact of mean airway pressure (Pmean), S/F ratio, OI, and P/FP ratio on mortality.

A total of 201 patients (with 1543 measurements) were included in the analysis. Overall, 522 (34%) were reclassified into either more or less severe categories. Patients who were classified as having severe ARDS based on the P/FP ratio had significantly lower P/FP ratio, oxygenation index, and A-a O2 gradient as compared to those classified as having severe ARDS based on the P/F ratio (p < 0.05) at all levels of ARDS severity. On multivariate regression analysis, only the OI significantly impacted mortality (p < 0.05).

We observed that the oxygen index and oxygen saturation index were more sensitive than the PaO_2/FiO₂ ratio and P/FP ratio. Additionally, only the oxygenation index had a significant impact on mortality. By including airway pressures in the calculation of the OI, its predictive ability is enhanced compared to using the S/F ratio, P/F ratio, or P/FP ratio.

The sensitivity of mortality by including Pmean is higher as compared to when only PEEP is taken into consideration. P/FP is a weak predictor of mortality as compared to OI and OSI.

Vadi SMR, Sanwalka N, Suthar D. Oxygenation Index, Oxygen Saturation Index vs PaO₂/FiO₂ *PEEP: A Secondary Analysis of OXIVA-CARDS Study. Indian J Crit Care Med 2024;28(10):917-922.