Elevated Central Venous to Arterial CO2 Difference Is Not Associated With Poor Clinical Outcomes After Cardiac Surgery With Cardiopulmonary Bypass in Children

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.

Correlation of venous to arterial carbon dioxide partial pressure difference with other cardiac output indices in patients undergoing intracardiac repair for tetralogy of fallot

Background

Clearance of tissue carbon dioxide by circulation is measured by venous to arterial carbon dioxide partial pressure difference (AVCO2) and is correlated with cardiac output (CO) in critically ill adult patients. This study aimed to correlate AVCO2 with other CO indices like arteriovenous oxygen saturation difference (AVO2), central venous oxygen saturation (ScVO2), and serum lactate in pediatric patients undergoing intracardiac repair (ICR) for tetralogy of Fallot (TOF).

Methods

We conducted a prospective observational study in 50 patients, of age 5 months to 5 years, undergoing ICR for TOF and analyzed AVO2, AVCO2, ScVO2, and lactate from arterial and venous blood gas pairs obtained at different time intervals from admission to pediatric intensive care unit (PICU) (T0), at 6 h (T1), 12 h (T2), 24 h (T3), and 48 h (T4) postoperatively. Bivariate correlations were analyzed using Pearson for parametric variables.

Results

Admission AVCO2 was not correlated with AVO2 (R2 = 0.166, P = 0.246), ScVO2 (R2 = -2.2, P = 0.124), and lactate (R2 = -0.07, P = 0.624). At T1, AVCO2 was correlated with AVO2 (R2 = 0.283, P = 0.0464) but not with ScVO2 (R2 = - 0.25, P = 0.079) and lactate (R2 = -0.07, P = 0.623). At T2, T3 and T4, AVCO2 was correlated with AVO2 (R2 = 0.338,0.440 & 0.318, P = 0.0162, 0.0013, and 0.024), ScVO2 (R2 = - 0.344, - 0.488, and -0.366; P = 0.0143, <0.0001, and 0.017), and lactate (R2 = 0.305, 0.467 and 0.607; P = 0.0314, 0.00062 and <0.0001). AVCO2 was negatively correlated with ScVO2. No correlation observed between admission AVCO2 and mechanical ventilation duration. Two nonsurvivors had higher value of admission AVCO2 compared to survivors.

Conclusion

AVCO2 is correlated with other CO surrogates like AVO2, ScVO2, and lactate in pediatric patients undergoing ICR for TOF.

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.

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.

Elevated Arterial-Central Venous Carbon Dioxide Partial Pressure Difference Indicates Poor Prognosis in the Early Postoperative Period of Open Heart Surgery in Infants with Congenital Heart Disease

BACKGROUND

Elevated arterial-central venous carbon dioxide partial pressure difference (AVCO₂) may be an important marker to predict tissue and organ hypoperfusion in adults. We analyzed the hemodynamic data of infants with congenital heart disease who underwent corrective repair with cardiopulmonary bypass (CPB) to identify whether AVCO₂ has clinical significance in early postoperative tissue hypoperfusion, occurrence of complications, and clinical outcomes.

METHODS

Infants with clinical conditions of hypoperfusion, without volume responsiveness and with ineffective initial treatment, within 3 h of cardiac surgery were enrolled in this study. A pulse contour cardiac output catheter was used to monitor the cardiac index (CI). Eight measurements of arterial blood gas and central venous blood gas were taken within 42 h after surgery. Clinical data of all patients were recorded.

RESULTS

A total of 69 children were enrolled in this study. Arteriovenous oxygen difference, AVCO₂, lactic acid level, and vasoactive inotropic score in the hypoperfusion group (oxygen supply/oxygen consumption ratio [DO₂/VO₂] of ≤ 2) were significantly higher than those in the non-hypoperfusion group (DO₂/VO₂ > 2), while the CI in the hypoperfusion group was significantly lower than that in the non-hypoperfusion group. The cutoff value of AVCO₂ to predict DO₂/VO₂ ≤ 2 was 12.3 within 42 h of surgery with area under the curve of 0.84. High AVCO₂ is more likely to be associated with some complications and prolonged mechanical ventilation and length of stay in the intensive care unit.

CONCLUSION

Elevated AVCO₂ within 42 h of CPB in infants is associated with tissue and organ hypoperfusion and incidence of complications. Persistent or repeated increase in AVCO₂ indicates poor prognosis.

Veno-arterial CO2 difference and cardiac index in children after cardiac surgery

Veno-arterial CO2 difference has been considered as a marker of low cardiac output. This study aimed to evaluate the correlation between veno-arterial CO2 difference and cardiac index estimated by MostCareTM in children after cardiac surgery and its association with other indirect perfusion parameters and the complex clinical course (vasoactive inotropic score above 15 or length of stay above 5 days).Data from 40 patients and 127 arterial and venous CO2 measurements for gap calculation taken 0-5 days postoperatively were available. The median (range) veno-arterial CO2 difference value was 9 (1-25 mmHg). The correlation between veno-arterial CO2 difference and cardiac index was not significant (r: -0.16, p = 0.08). However, there was a significant correlation between veno-arterial CO2 difference and vasoactive inotropic score (r: 0.21, p = 0.02), systolic arterial pressure (r: -0.43, p = 0.0001), dP/dtMAX (r: 0.26, p = 0.004), and arterio-venous O2 difference (r: 0.63, p = 0.0001). Systolic arterial pressure (OR 0.95, 95% CI 0.90-0.99), dP/dtMAX (OR 0.00, 95% CI 0.00-0.06), lactates (OR 1.87, 95% CI 1.21-3.31), and veno-arterial CO2 difference (OR 1.13, 95% CI 1.01-1.35) showed a significant univariate association with the complex clinical course. In conclusion, veno-arterial CO2 difference did not correlate with cardiac index estimated by MostCareTM in our cohort of post-cardiosurgical children, but it identified patients with the complex clinical course, especially when combined with other direct and indirect variables of perfusion.

High Central Venous-to-Arterial CO2 Difference is Associated With Poor Outcomes in Patients After Cardiac Surgery: A Propensity Score Analysis

PURPOSE

In contrast to arterial lactate, previous studies have proposed central venous-to-arterial CO2 difference (P (v-a)CO2) as a more useful guide for categorizing patients at risk of developing septic shock. It is worthwhile studying P (v-a)CO2 in determining whether it could serve as a useful predictor for poor postoperative outcomes in patients undergoing cardiac surgery. We investigated the ability of P(v-a)CO2 to predict poor outcomes of patients with postoperative cardiogenic shock.

METHODS

In total, 1,672 patients were enrolled in this study from January 1, 2014 to June 1, 2017. Of these patients, 143 exhibited complicated and poor outcomes. To address any bias, we derived a propensity score predicting the functions of P(v-a)CO2 on poor outcomes and matched 114 cases to 114 controls with a similar risk profile. In this cohort study, poor outcomes were defined as the occurrence of any adverse complications, including sudden death, cardiac arrest, extracorporeal membrane oxygenation, oliguria, and the administration of a large amount of vasoactive-inotropic drugs.

RESULTS

In propensity-matched patients, significant differences in P(v-a)CO2 (6.11 ± 2.94 mm Hg vs. 11.21 ± 5.22 mm Hg, P < 0.001) were noted between the control group and poor outcome group. The area under the receiver operating characteristic curve of P(v-a)CO2 (AUC: 0.837, 95% CI: 0.782-0.892) for the detection of poor outcomes was significantly better compared to that of the central venous oxygen saturation and arterial lactate. Additionally, there was a negative correlation between cardiac index and P(v-a)CO2 (R= -0.68, P < 0.001).

CONCLUSION

We have shown a correlation between P(v-a)CO2 to cardiac output which may be used as an alternative metric to predict the poor outcomes of patients with postoperative cardiogenic shock.

Central venous-to-arterial PCO2 difference, arteriovenous oxygen content and outcome after adult cardiac surgery with cardiopulmonary bypass: A prospective observational study

BACKGROUND

Rapid identification and treatment of tissue hypoxia reaching anaerobiosis (dysoxia) may reduce organ failure and the occurrence of major postoperative complications (MPC) after cardiac surgery. The predictive ability of PCO2-based dysoxia biomarkers, central venous-to-arterial PCO2 difference (ΔPCO2) and ΔPCO2 to arteriovenous oxygen content difference ratio, is poorly studied in this setting.

OBJECTIVES

We evaluated the ability of PCO2-based tissue dysoxia biomarkers, blood lactate concentration and central venous oxygen saturation measured 2 h after admission to the ICU as predictors of MPC.

DESIGN

A prospective, observational cohort study.

SETTING

Single-centre, academic hospital cardiovascular ICU.

PATIENTS

We included adult patients undergoing cardiac surgery with cardiopulmonary bypass and measured dysoxia biomarkers at ICU admission, and after 2, 6 and 24 h.

MAIN OUTCOME MEASURES

The primary endpoint was MPC, a composite of cardiac and noncardiac MPC evaluated in the 48 h following surgery. After univariate analysis of MPC covariates including dysoxia biomarkers measured at 2 h, multivariate logistic regression analyses were performed to identify the association of these biomarkers with MPC for confounders. Areas under the receiver operating characteristic curves were determined for biomarkers which remained independently associated with MPC.

RESULTS

MPC occurred in 56.5% of the 308 patients analysed. ΔPCO2, blood lactate concentration and central venous oxygen saturation measured at 2 h, but not ΔPCO2 to arteriovenous oxygen content difference ratio, were significantly associated with MPC. However, only ΔPCO2 was independently associated with MPC after multivariate analysis. The areas under the receiver operating characteristic curves of ΔPCO2 measured at 2 h for MPC prediction was 0.64 (95% CI 0.57 to 0.70, P < 0.001).

CONCLUSION

After cardiac surgery with cardiopulmonary bypass, ΔPCO2 measured 2 h after ICU admission was the only dysoxia biomarker independently associated with MPC, but with limited performance.

TRIAL REGISTRATION

ClinicalTrials.gov, NCT03107572.

Value of Central Venous to Arterial CO2 Difference after Early Goal-directed Therapy in Septic Shock Patients

Background and aims

Venous to arterial difference of carbon dioxide (Pv–aCO₂) tracks tissue blood flow. We aimed to evaluate if Pv–aCO₂ measured from a superior central vein sample is a prognostic index (ICU length of stay, SOFA score, 28th mortality rate) just after early goal-directed therapy (EGDT)comparing its ICU admission values between patients with normal and abnormal (>6 mm Hg) Pv–aCO₂. As secondary objectives, we evaluated the relationship of Pv–aCO₂ with other variables of perfusion during the 24 hours that followed EGDT.

Materials and methods

Prospective observational study conducted in an academic ICU adult septic shock patients after a 6-hour complete EGTD. Hemodynamic measurements, arterial/central venous blood gases, and arterial lactate were obtained on ICU admission and after 6, 18 and 24 hours.

Results

Sixty patients were included. Admission Pv–aCO₂ values showed no prognostic value. Admission Pv–aCO₂ (ROC curve 0.527 [CI 95% 0.394 to 0.658]) values showed low specificity and sensitivity as predictors of mortality. There was a difference observed in the mean Pv–aCO₂ between nonsurvivors (NS) and survivors (S) after 6 hours. Central venous oxygen saturation (ScvO₂) and Pv–aCO₂ showed significant correlation (R2 = –0.41, P < 0.0001). Patients with normal ScvO₂ (>70%) and abnormal Pv–aCO₂ (>6 mm Hg) showed higher SOFA scores. Normal Pv–aCO₂ group cleared their lactate levels in comparison to the abnormal Pv–aCO₂ group.

Conclusion

In septic shock, admission Pv–aCO₂ after EGDT is not related to worse outcomes. An abnormal Pv–aCO₂ along with a normal ScvO₂ is related to organ dysfunction.

How to cite this article

Araujo DT, Felice VB, Meregalli AF, Friedman G. Value of Central Venous to Arterial CO₂ Difference after Early Goal-directed Therapy in Septic Shock Patients. Indian J Crit Care Med 2019;23(10):449–453.