The Use of the Oxygenation Stretch Index to Predict Outcomes in Mechanically Ventilated PatientsWith COVID-19 ARDS

BACKGROUND: In ARDS caused by COVID-19 pneumonia, appropriate adjustment of physiologic parameters based on lung stretch or oxygenation may optimize the ventilatory strategy. This study aims to describe the prognostic performance on 60-d mortality of single and composite respiratory variables in subjects with COVID- 19 ARDS who are on mechanical ventilation with a lung-protective strategy, including the oxygenation stretch index combining oxygenation and driving pressure (Delta P). METHODS: This single-center observational cohort study enrolled 166 subjects on mechanical ventilation and diagnosed with COVID-19 ARDS. We evaluated their clinical and physiologic characteristics. The primary study outcome was 60-d mortality. Prognostic factors were evaluated through receiver operating characteristic analysis, Cox proportional hazards regression model, and Kaplan-Meier survival curves. RESULTS: Mortality at day 60 was 18.1%, and hospital mortality was 22.9%. Oxygenation, DP, and composite variables were tested: oxygenation stretch index (P-aO2 /F-IO2 divided by Delta P) and Delta P 3 4 + breathing frequency (f) (Delta P 3 4 + f). At both day 1 and day 2 after inclusion, the oxygenation stretch index had the best area under the receiver operating characteristic curve (oxygenation stretch index on day 1 0.76 (95% CI 0.67-0.84) and on day 2 0.83 (95% CI 0.76-0.91) to predict 60-d mortality, although without significant difference from other indexes. In multivariable Cox regression, Delta P, PaO2 /FIO2, Delta P 3 4 + f, and oxygenation stretch index were all associated with 60-d mortality. When dichotomizing the variables, Delta P >= 14, P-aO2 / F-IO2 >= 152 mm Hg, Delta P x 4 + f >= 80, and oxygenation stretch index < 7.7 showed lower 60-d survival probability. At day 2, after optimization of ventilatory settings, the subjects who persisted with the worse cutoff values for the oxygenation stretch index showed a lower probability of survival at 60 d compared with day 1; this was not the case for other parameters. CONCLUSIONS: The oxygenation stretch index, which combines P-aO2 /F-IO2 and DP, is associated with mortality and may be useful to predict clinical outcomes in COVID-19 ARDS.