Veno-arterial CO(2) difference and cardiac index in children after cardiac surgery

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 CO2-derived parameters in predicting major postoperative complications (MPC) after cardiac surgery with cardiopulmonary bypass.

Methods

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.

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 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.

Conclusions

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.

Veno-Arterial Partial Pressure of Carbon Dioxide Difference as a Metric of Systemic Oxygen Delivery: Insights from a Correlative Meta-Analysis

The assessment of cardiac output and adequacy of systemic oxygen delivery in children after cardiac surgery require the use of an aggregate of hemodynamic monitors and blood tests. There are previously published data regarding the utility of the veno-arterial partial pressure of carbon dioxide difference (AVDco2) to help with this. This study pooled data on the correlation of AVDco2 with other metrics of cardiac output and systemic oxygen delivery such as arteriovenous oxygen saturation difference, venous saturation, and serum lactate. A systematic review of the literature was done to identify studies analyzing the correlation of AVDco2 with other hemodynamic and laboratory values. Data were extracted, and correlation coefficients were pooled for each specific comparison to create a point estimate for the overall correlation. A total of four studies with 350 patients and 809 paired blood gases were pooled. Adequate data were available to assess the correlation of AVDco2 with arteriovenous oxygen saturation difference, venous saturation, and serum lactate. There was a significant, moderate correlation with arteriovenous oxygen saturation difference and venous saturation. A significant, weak correlation with serum lactate was found. The AVDco2 has significant, moderate correlations with other metrics of the adequacy of systemic oxygen delivery such as arteriovenous oxygen saturation difference and venous saturation. There was a significant but only weak correlation with serum lactate. AVDco2 may be complementary to assess the adequacy of cardiac output and systemic oxygen delivery.

Use of CO2-Derived Variables in Cardiac Intensive Care Unit: Pathophysiology and Clinical Implications

Shock is a life-threatening condition, and its timely recognition is essential for adequate management. Pediatric patients with congenital heart disease admitted to a cardiac intensive care unit (CICU) after surgical corrections are particularly at risk of low cardiac output syndrome (LCOS) and shock. Blood lactate levels and venous oxygen saturation (ScVO₂) are usually used as shock biomarkers to monitor the efficacy of resuscitation efforts, but they are plagued by some limitations. Carbon dioxide (CO₂)-derived parameters, namely veno-arterial CO₂ difference (ΔCCO₂) and the VCO₂/VO₂ ratio, may represent a potentially valuable addition as sensitive biomarkers to assess tissue perfusion and cellular oxygenation and may represent a valuable addition in shock monitoring. These variables have been mostly studied in the adult population, with a strong association between ΔCCO₂ or VCO₂/VO₂ ratio and mortality. In children, particularly in CICU, few studies looked at these parameters, while they reported promising results on the use of CO₂-derived indices for patients' management after cardiac surgeries. This review focuses on the physiological and pathophysiological determinants of ΔCCO₂ and VCO₂/VO₂ ratio while summarizing the actual state of knowledge on the use of CO₂-derived indices as hemodynamical markers in CICU.

Capnodynamics - noninvasive cardiac output and mixed venous oxygen saturation monitoring in children

Hemodynamic monitoring in children is challenging for many reasons. Technical limitations in combination with insufficient validation against reference methods, makes reliable monitoring systems difficult to establish. Since recent studies have highlighted perioperative cardiovascular stability as an important factor for patient outcome in pediatrics, the need for accurate hemodynamic monitoring methods in children is obvious. The development of mathematical processing of fast response mainstream capnography signals, has allowed for the development of capnodynamic hemodynamic monitoring. By inducing small changes in ventilation in intubated and mechanically ventilated patients, fluctuations in alveolar carbon dioxide are created. The subsequent changes in carbon dioxide elimination can be used to calculate the blood flow participating in gas exchange, i.e., effective pulmonary blood flow which equals the non-shunted pulmonary blood flow. Cardiac output can then be estimated and continuously monitored in a breath-by-breath fashion without the need for additional equipment, training, or calibration. In addition, the method allows for mixed venous oxygen saturation (SvO₂) monitoring, without pulmonary artery catheterization. The current review will discuss the capnodyamic method and its application and limitation as well as future potential development and functions in pediatric patients.