Lactate and CO2-derived parameters are not predictive factors of major postoperative complications after cardiac surgery with cardiopulmonary bypass: a diagnostic accuracy study

Purpose This study aimed to compare the performance of lactate and CO 2 -derived parameters in predicting major postoperative complications (MPC) after cardiac surgery with cardiopulmonary bypass. Methods Lactate and CO 2 -derived parameters, including the venous-arterial difference in CO 2 partial pressure (Pv-aCO 2 ), the venous-arterial difference in CO 2 partial pressure to arterial-venous O 2 content ratio (Pv-aCO 2 /Ca-vO 2 ), and the venous-arterial difference in CO 2 content to arterial-venous O 2 content ratio (Cv-aCO 2 /Ca-vO 2 ) at ICU admission, 3 h, 6 h, and 12 h later were collected. Receiver-operating characteristics (ROC) curve analysis was carried out to assess the predictive performance. Univariate and multivariate logistic regression analyses were performed to identify independent predictors of MPC. Results MPC occurred in 77 (54.2%) of 142 patients. No significant difference was observed between the MPC and no-MPC groups regarding lactate and CO 2 -derived parameters. The area under the curves (AUCs) were 0.532 (0.446–0.616) for lactate, 0.559 (0.473–0.642) for Pv-aCO 2 , 0.617 (0.532–0.697) for Pv-aCO 2 /Ca-vO 2 , and 0.625 (0.540–0.705) for Cv-aCO 2 /Ca-vO 2 , respectively, and there was no significant difference between the parameters. In the post-hoc analysis, all parameters' AUCs were lower than 0.75 in predicting acute renal failure, and there was no significant difference between these parameters. Cv-aCO 2 /Ca-vO 2 at 12 h yielded the highest AUC of 0.853 (0.784–0.907) in predicting mortality and the highest AUC of 0.808 (0.733–0.869) in predicting delirium. In multivariate analysis, hypertension, surgery duration, and PaO 2 /FiO 2 were identified as independent predictors of MPC, while lactate and CO 2 -derived parameters lost statistical significance after adjustment for covariates. Conclusions Lactate and CO 2 -derived parameters cannot be used as reliable indicators to predict the occurrence of MPC after cardiopulmonary bypass. Instead, traditional clinical factors such as hypertension, extended surgical duration, and impaired oxygenation emerged as the most reliable risk indicators.