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

## TL;DR

This study found that lactate and CO2-derived parameters are not reliable predictors of major postoperative complications after heart surgery, with traditional factors like hypertension and surgery duration being more useful.

## Contribution

The study demonstrates that lactate and CO2-derived parameters lack predictive value for major postoperative complications after cardiac surgery.

## Key findings

- Lactate and CO2-derived parameters showed no significant predictive power for major postoperative complications.
- Traditional clinical factors like hypertension and surgery duration were identified as independent predictors of complications.
- Cv-aCO2/Ca-vO2 at 12 hours showed the best predictive performance for mortality and delirium.

## Abstract

This study aimed to compare the performance of lactate and CO2-derived parameters in predicting major postoperative complications (MPC) after cardiac surgery with cardiopulmonary bypass.

Lactate and CO2-derived parameters, including the venous-arterial difference in CO2 partial pressure (Pv-aCO2), the venous-arterial difference in CO2 partial pressure to arterial-venous O2 content ratio (Pv-aCO2/Ca-vO2), and the venous-arterial difference in CO2 content to arterial-venous O2 content ratio (Cv-aCO2/Ca-vO2) 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.

MPC occurred in 77 (54.2%) of 142 patients. No significant difference was observed between the MPC and no-MPC groups regarding lactate and CO2-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-aCO2, 0.617 (0.532–0.697) for Pv-aCO2/Ca-vO2, and 0.625 (0.540–0.705) for Cv-aCO2/Ca-vO2, 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-aCO2/Ca-vO2 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 PaO2/FiO2 were identified as independent predictors of MPC, while lactate and CO2-derived parameters lost statistical significance after adjustment for covariates.

Lactate and CO2-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.