Comparison of the venous–arterial CO₂ to arterial–venous O₂ content difference ratio with the venous–arterial CO₂ gradient for the predictability of adverse outcomes after cardiac surgery

This study aimed to compare the prognostic performance of the ratio of mixed and central venous–arterial CO₂ tension difference to arterial–venous O₂ content difference (Pv-aCO₂/Ca-vO₂ and Pcv-aCO₂/Ca-cvO₂, respectively) with that of the mixed and central venous-to-arterial carbon dioxide gradient (Pv-aCO₂ and Pcv-aCO₂, respectively) for adverse events after cardiac surgery. One hundred and ten patients undergoing cardiac surgery with cardiopulmonary bypass were enrolled. After catheter insertion, three blood samples were withdrawn simultaneously through arterial pressure, central venous, and pulmonary artery catheters, before and at the end of the operation, and preoperative and postoperative values were determined. The primary end-point was set as the incidence of postoperative major organ morbidity and mortality (MOMM). Receiver operating characteristic (ROC) curve and multivariate logistic regression analyses were performed to evaluate the prognostic reliability of Pv-aCO₂, Pcv-aCO₂, Pv-aCO₂/Ca-vO₂, and Pcv-aCO₂/Ca-cvO₂ for MOMM. MOMM events occurred in 25 patients (22.7%). ROC curve analysis revealed that both postoperative Pv-aCO₂/Ca-vO₂ and Pcv-aCO₂/Ca-cvO₂ were significant predictors of MOMM. However, postoperative Pv-aCO₂ was the best predictor of MOMM (area under the curve [AUC]: 0.804; 95% confidence interval [CI] 0.688–0.921), at a 5.1-mmHg cut-off, sensitivity was 76.0%, and specificity was 74.1%. Multivariate analysis revealed that postoperative Pv-aCO₂ was an independent predictor of MOMM (odds ratio [OR]: 1.42, 95% CI 1.01–2.00, p = 0.046) and prolonged ICU stay (OR: 1.45, 95% CI 1.05–2.01, p = 0.024). Pv-aCO₂ at the end of cardiac surgery was a better predictor of postoperative complications than Pv-aCO₂/Ca-vO₂ and Pcv-aCO₂/Ca-cvO₂.