The Pv-aCO₂/Ca-vO₂ ratio as a predictor of mortality in patients with severe acute respiratory distress syndrome related to COVID-19

Objective To evaluate the central venous-to-arterial carbon dioxide difference combined with arterial-to-venous oxygen content difference (Delta Pv- aCO2/Delta Ca- vO2 ratio) as a predictor of mortality in patients with COVID-19-related severe acute respiratory distress syndrome (ARDS). Methods Patients admitted to the intensive care unit with severe ARDS secondary to SARS-CoV-2, and invasive mechanical ventilation were included in this single-center and retrospective cohort study performed between April 18, 2020, and January 18, 2022. The tissue perfusion indexes (lactate, central venous oxygen saturation [ScvO2], and venous-to-arterial carbon dioxide pressure difference [Delta Pv- aCO2]), anaerobic metabolism index (Delta Pv- aCO2/Delta Ca-vO2 ratio), and severity index (Simplified Acute Physiology Score II [SAPSII]) were evaluated to determine its association with the mortality through Cox regression analysis, Kaplan-Meier curve and receiver operating characteristic (ROC) curve. Results One hundred fifteen patients were included in the study and classified into two groups, the survivor group (n = 54) and the non-survivor group (n = 61). The lactate, ScvO(2),Delta Pv-aCO(2), and Delta Pv-aCO(2)/Delta Ca-vO(2) ratio medians were 1.6 mEq/L, 75%, 5 mmHg, and 1.56 mmHg/ mL, respectively. The Delta Pv-aCO(2)/Delta Ca-vO(2) ratio (Hazard Ratio (HR) = 1.17, 95% confidence interval (CI) = 1.06-1.29, p = 0.001) was identified as a mortality biomarker for patients with COVID-19-related severe ARDS. The area under the curve for Delta Pv-aCO(2)/Delta Ca-vO(2) ratio was 0.691 (95% CI 0.598-0.774, p = 0.0001). The best cut-off point for Delta Pv-aCO(2)/Delta Ca-vO(2) ratio was >2.14 mmHg/mL, with a sensitivity of 49.18%, specificity of 85.19%, a positive likelihood of 3.32, and a negative likelihood of 0.6. The Kaplan-Meier curve showed that survival rates were significantly worse in patients with values greater than this cut-off point. Conclusions The Delta Pv-aCO(2)/Delta Ca-vO(2) ratio could be used as a predictor of mortality in patients with severe ARDS secondary to SARS-CoV-2.