Progressive changes in pulmonary gas exchange during invasive respiratory support for COVID‐19 associated acute respiratory failure: A retrospective study of the association with 90‐day mortality

Background Ratio of arterial pressure of oxygen and fraction of inspired oxygen (P/F ratio) together with the fractional dead space (Vd/Vt) provides a global assessment of pulmonary gas exchange. The aim of this study was to assess the potential value of these variables to prognosticate 90‐day survival in patients with COVID‐19 associated ARDS admitted to the Intensive Care Unit (ICU) for invasive ventilatory support. Methods In this single‐center observational, retrospective study, P/F ratios and Vd/Vt were assessed up to 4 weeks after ICU‐admission. Measurements from the first 2 weeks were used to evaluate the predictive value of P/F ratio and Vd/Vt for 90‐day mortality and reported by the adjusted hazard ratio (HR) and 95% confidence intervals [95%CI] by Cox proportional hazard regression. Results Almost 20,000 blood gases in 130 patients were analyzed. The overall 90‐day mortality was 30% and using the data from the first ICU week, the HR was 0.85 [0.77–0.94] for every 10 mmHg increase in P/F ratio and 1.61 [1.20–2.16] for every 0.1 increase in Vd/Vt. In the second week, the HR for 90‐day mortality was 0.82 [0.75–0.89] for every 10 mmHg increase in P/F ratio and 1.97 [1.42–2.73] for every 0.1 increase in Vd/Vt. Conclusion The progressive changes in P/F ratio and Vd/Vt in the first 2 weeks of invasive ventilatory support for COVID‐19 ARDS were significant predictors for 90‐day mortality.