The Use of the Ratio between the Veno-arterial Carbon Dioxide Difference and the Arterial-venous Oxygen Difference to Guide Resuscitation in Cardiac Surgery Patients with Hyperlactatemia and Normal Central Venous Oxygen Saturation

Analysis of P(v-a)CO2/C(a-v)O2 Ratio and Other Perfusion Markers in a Population of 98 Pediatric Patients Undergoing Cardiac Surgery

BACKGROUND

The so-called Low Cardiac Output Syndrome (LCOS) is one of the most common complications in pediatric patients with congenital heart disease undergoing corrective surgery. LCOS requires high concentrations of inotropes to support cardiac contractility and improve cardiac output, allowing for better systemic perfusion. To date, serum lactate concentrations and central venous oxygen saturation (ScVO2) are the most commonly used perfusion markers, but they are not completely reliable in identifying a state of global tissue hypoxia. The study aims to evaluate whether the venoarterial carbon dioxide difference/arterial-venous oxygen difference ratio [P(v-a)CO2/C(a-v)O2] can be a good index to predict the development of LCOS in the aforementioned patients, so as to treat it promptly.

METHODS

This study followed a population of 98 children undergoing corrective cardiac surgery from June 2018 to October 2020 at the Department of Cardiac Surgery of University Hospital Integrated Trust and their subsequent admission at the Postoperative Cardiothoracic Surgery Intensive Care Unit. During the study, central arterial and venous blood gas analyses were carried out before and after cardiopulmonary bypass (CPB) (pre-CPB and post-CPB), at admission to the intensive care unit, before and after extubation, and at any time of instability or modification of the patient's clinical and therapeutic conditions.

RESULTS

The data analysis shows that 46.9% of the children developed LCOS (in line with the current literature) but that there is no statistically significant association between the P(v-a)CO2/C(a-v)O2 ratio and LCOS onset. Despite the limits of statistical significance, however, a 31% increase in the ratio emerged from the pre-CPB phase to the post-CPB phase when LCOS is present.

CONCLUSIONS

This study confirms a statistically significant association between the most used markers in adult patients (serum lactate concentration, ScVO2, and oxygen extraction ratio-ERO2) measured in the pre-CPB phase and the incidence of LCOS onset, especially in patients with hemodynamic instability before surgery.

Ratio of carbon dioxide veno-arterial difference to oxygen arterial-venous difference is not associated with lactate decrease after fluid bolus in critically ill patients with hyperlactatemia: results from a prospective observational study

BACKGROUND

High ratio of the carbon dioxide veno-arterial difference to the oxygen arterial-venous difference (P_vaCO₂/C_avO₂) is associated with fluid bolus (FB) induced increase in oxygen consumption (VO₂). This study investigated whether P_vaCO₂/C_avO₂ was associated with decreases in blood-lactate levels FB in critically ill patients with hyperlactatemia.

METHODS

This prospective observational study examined adult patients in the intensive care unit (ICU) with lactate levels > 1.5 mmol/L who received FBs. Blood-lactate levels were measured before and after FB under unchanged metabolic, respiratory, and hemodynamic conditions. The primary outcome was blood-lactate levels after FB. Significant decreases in blood-lactate levels were considered as blood-lactate levels < 1.5 mmol/L or a decrease of more than 10% compared to baseline.

RESULTS

The study enrolled 40 critically ill patients, and their median concentration of blood lactate was 2.6 [IQR:1.9 - 3.8] mmol/L. There were 27 (68%) patients with P_vaCO₂/C_avO₂ ≥ 1.4 mmHg/ml, and 10 of them had an increase in oxygen consumption (dVO₂) ≥ 15% after FB, while 13 (32%) patients had P_vaCO₂/C_avO₂ < 1.4 mmHg/ml before FB, and none of them had dVO₂ ≥ 15% after FB. FB increased the cardiac index in patients with high and low preinfusion P_vaCO₂/C_avO₂ (13.4% [IQR: 8.3 - 20.2] vs. 8.8% [IQR: 2.9 - 17.4], p = 0.34). Baseline P_vaCO₂/C_avO₂ was not found to be associated with a decrease in blood lactate after FB (OR: 0.88 [95% CI: 0.39 - 1.98], p = 0.76). A positive correlation was observed between changes in blood lactate and baseline P_vaCO₂/C_avO₂ (r = 0.35, p = 0.02).

CONCLUSIONS

In critically ill patients with hyperlactatemia, P_vaCO₂/C_avO₂ before FB cannot be used to predict decreases in blood-lactate levels after FB. Increased P_vaCO₂/C_avO₂ is associated with less decrease in blood-lactate levels.

P(v-a)CO2/C(a-v)O2 as a red blood cell transfusion trigger and prognostic indicator for sepsis-related anaemia: protocol for a prospective cohort study

INTRODUCTION

Red blood cell (RBC) transfusion primarily aims to improve oxygen transport and tissue oxygenation. The transfusion strategy based on haemoglobin concentration could not accurately reflect cellular metabolism. The ratio of venous-arterial carbon dioxide tension difference to arterial-venous oxygen content difference (P(v-a)CO₂/C(a-v)O₂) is a good indicator of cellular hypoxia. We aim to explore the influence of P(v-a)CO₂/C(a-v)O₂ as an RBC transfusion trigger on outcomes in septic shock patients.

METHODS AND ANALYSIS

The study is a single-centre prospective cohort study. We consecutively enrol adult septic shock patients requiring RBC transfusion at intensive care unit (ICU) admission or during ICU stay. P(v-a)CO₂/C(a-v)O₂ will be recorded before and 1 hour after each transfusion. The primary outcome is ICU mortality. Binary logistic regression analyses will be performed to detect the independent association between P(v-a)CO₂/C(a-v)O₂ and ICU mortality. A cut-off value for P(v-a)CO₂/C(a-v)O₂ will be obtained by maximising the Youden index with the receiver operator characteristic curve. According to this cut-off value, patients included will be divided into two groups: one with the P(v-a)CO₂/C(a-v)O₂ >cut-off and the other with the P(v-a)CO₂/C(a-v)O₂ ≤cut off. Differences in clinical outcomes between the two groups will be assessed after propensity matching.

ETHICS AND DISSEMINATION

The study has been approved by the Institutional Review Board of Affiliated Hospital of Weifang Medical University (wyfy-2021-ky-059). Findings will be disseminated through conference presentations and peer-reviewed journals.

TRIAL REGISTRATION NUMBER

ChiCTR2100051748.

PCO2 gap, its ratio to arteriovenous oxygen content, ScvO2 and lactate in high-risk abdominal surgery patients: An observational study

BACKGROUND

The difference between arterial and central venous carbon dioxide partial pressure (PCO₂ gap), a marker of oxygen delivery (DO₂) and oxygen consumption (VO₂) adequacy, has been evaluated as a promising prognostic tool in intensive care unit (ICU) patients. We therefore sought to study the association between intraoperative PCO₂ gap and postoperative complications (POC) in the perioperative setting of elective major abdominal surgery.

METHODS

We conducted a single-centre prospective observational study. All adult patients who underwent major planned abdominal surgery were eligible. PCO₂ gap was measured every 2 hours during surgery, at ICU admission and repeated 12 hours and 24 hours later. Severe POC within 28 days after surgery were defined as complications graded 3 or more according to Clavien-Dindo classification. Following a univariate analysis, a multivariable analysis using a logistic regression model was performed.

RESULTS

Ninety patients were included and divided into two groups according to the occurrence of POC. No significant difference was found between groups regarding baseline characteristics at inclusion. Thirty-nine (43%) patients developed postoperative complications. The median [IQR] intraoperative PCO₂ gap was significantly higher in patients who had complications (6.5 [5.5-7.3] mmHg) compared to those who did not (5.0 [3.9-5.8] mmHg; p < 0.001). The area under the receiver operating characteristic curve for occurrence of POC was 0.78 for the PCO₂ gap. After multivariable analysis, PCO₂ gap was found independently associated with POC (OR: 14.9, 95% CI [4.68-60.1], p < 0.001) with a threshold value of 6.2 mmHg. The duration of surgery (OR: 1.01, 95% CI [1.00; 1.01], p = 0.04) and the need for vasoactive support during surgery (OR: 5.76, 95% CI [1.72; 24.1], p = 0.006) were also independently associated with POC.

CONCLUSION

Intraoperative PCO₂ gap is a relevant predictive factor of severe postoperative complications in high-risk elective surgery patients.

TRIAL REGISTRATION

ClinicalTrials.gov, NCT03914976.

Performance of Lactate and CO2-Derived Parameters in Predicting Major Postoperative Complications After Cardiac Surgery With Cardiopulmonary Bypass: Protocol of a Diagnostic Accuracy Study

Background: CO₂-derived parameters are increasingly used to identify either low-flow status or anaerobic metabolism in shock resuscitation. However, the performance of CO₂-derived parameters in cardiac surgical patients is poorly understood. This study aims to compare the performance of lactate and CO₂-derived parameters in predicting major postoperative complications after cardiac surgery with cardiopulmonary bypass. Methods: This is a prospective, single-center, diagnostic accuracy study. All patients who receive elective cardiac surgery involving cardiopulmonary bypass will be screened for study eligibility. Blood samples will be taken for the calculation of CO₂-derived parameters, including the venous-arterial difference in CO₂ partial pressure (PCO₂ gap), venous-arterial difference in CO₂ content to arterial-venous O₂ content ratio (Cv-aCO₂/Ca-vO₂), and venous-arterial difference in CO₂ partial pressure to arterial-venous O₂ content ratio (Pv-aCO₂/Ca-vO₂) at ICU admission, and 3, 6, and 12 h later. Baseline, perioperative data will be collected daily for 7 days; patients will be followed up for 28 days to collect outcome data. The primary endpoint is the occurrence of major postoperative complications. Receiver-operating characteristics (ROC) curve analysis will be carried out to assess the predictive performance of lactate and CO₂-derived parameters. The performance of the ROC curves will be compared. Discussion: The performance of lactate and CO₂-derived parameters in predicting major postoperative complications will be investigated in the non-sepsis population, which has not been extensively investigated. Our study will compare the two surrogates of respiratory quotient directly, which is an important strength. Trial Registration: ChiCTR, ChiCTR2000029365. Registered January 26th, 2020, http://www.chictr.org.cn/showproj.aspx?proj=48744.

The Ability of Carbon Dioxide-Derived Indices to Predict Adverse Outcome After Cardiac Surgery

OBJECTIVE

The objective of this study was to assess whether the central venous-to-arterial carbon dioxide partial-pressure difference (ΔPCO₂) and the ratio of the ΔPCO₂ to the arterial-venous difference in oxygen content (ΔPCO₂/Ca-vO₂) predict postoperative complications (PC) after cardiac surgery.

DESIGN

Prospective, observational, noninterventional study.

PARTICIPANTS

The study comprised 60 patients undergoing cardiac surgery with cardiopulmonary bypass.

INTERVENTIONS

The primary endpoint was the occurrence of PC. Data were first analyzed in two groups based on the occurrence of PC. Then, receiver operating characteristic curves of the ΔPCO₂ and the ΔPCO₂/Ca-vO₂ ratio were analyzed for the prediction of PC.

MEASUREMENTS AND MAIN RESULTS

Among the study participants, 22 (36.7%) experienced PC. The death rate was 18.3%. The present study found that the ΔPCO₂ and the ΔPCO₂/Ca-vO₂ ratio predicted the occurrence of PC with areas under the curve of 0.702 and 0.666, respectively. The best thresholds of these markers were 8.3 mmHg for the ΔPCO₂ and 2.16 mmHg/mL for the ΔPCO₂/Ca-vO₂ ratio. A significant difference was found for these indicators between the groups with and without PC. The ΔPCO₂ and the ΔPCO₂/Ca-vO₂ ratio were significantly correlated to EuroSCORE II, duration of aortic clamping, majority of prognostic scores the first two days postoperatively, and the lactate level. The ΔPCO₂/Ca-vO₂ ratio is predictive of hyperlactatemia >2 mmol/L, with an area under the curve of 0.787.

CONCLUSION

The ΔPCO₂ and the ΔPCO₂/Ca-vO₂ ratio predict the occurrence of complications in cardiac surgery.

Role of central venous - Arterial pCO2 difference in determining microcirculatory hypoperfusion in off-pump coronary artery bypass grafting surgery

Background:

Cardiac surgery is frequently associated with macro and microcirculatory hypoperfusion. Patients with normal central venous oxygen saturation (Scvo2) also suffer from hypoperfusion. We hypothesized that monitoring central venous-arterial pco2 difference (dCO₂) could also serve as additional marker in detecting hypoperfusion in cardiac surgery patient.

Methods:

This is a prospective observational study. Patients undergoing off-pump coronary artery bypass grafting included in this study. The dCO2 was measured postoperatively. The patients with a ScvO2 ≥70% were divided in to 2 groups, the high-dCO2 group (≥8 mmHg) and the low-dCO2 group (<8 mmHg).

Results:

The 65 patient had scvO₂ ≥70%. Out of these, 20 patients were assigned to the high dCO₂ group and 45 patients to the low dCO₂ group. Patients with high dco2 had higher lactate levels after ICU admission. They also had significantly prolonged need for mechanical ventilation (14.90 ± 10.33 vs 10 ± 9.65, P = 0.0402), ICU stay (5.05 ± 2.52 d vs 3.75 ± 2.36 d, P = 0.049) and hospital stay (12.25 ± 5.90 d vs 8.57 ± 5.55 d P = 0.018). The overall rate of post-operative complications was similar in both the group.

Conclusion:

The present study demonstrates dCO₂ as an easy to assess and routinely available tool to detect global and microcirculatory hypoperfusion in off-pump CABG patients, with assumed adequate fluid status and ScvO₂ as a hemodynamic goal. We observed that high dCO₂ (>8 mmHg) was associated with decreased DO₂I, increased oxygen extraction ratio, the longer need for mechanical ventilation and longer ICU stay.

Utility of venous-to-arterial carbon dioxide changes to arteriovenous oxygen content ratios in the prognosis of severe sepsis and septic shock: A systematic review and meta-analysis

Background:

Sepsis patients with insufficient tissue perfusion and hypoxia should be identified and resuscitated immediately. Recently, venous-to-arterial carbon dioxide pressure changes and the arteriovenous oxygen content difference ratio (Pcv-aCO2/Ca-vO2) as a predictor of tissue perfusion recovery and poor prognosis.

Objectives:

Pcv-aCO2/Ca-vO2 is a substitute for respiratory entropy, the elevation of which indicates a lack of tissue perfusion. Pcv-aCO2/Ca-vO2 can be used as an indicator to predict the prognosis of patients with sepsis or septic shock, but its prognostic value has not been fully evaluated. Here, we have performed a meta-analysis to assess its predictive value for mortality.

Methods:

Meta-analysis of Observational Studies in Epidemiology group guidelines were followed for this meta-analysis. We searched the comprehensive electronic databases of PubMed, EMBASE, Web of Science, and Cochrane libraries from inception to March 2019, using the terms including “venous-arterial,” “carbon dioxide,” “Shock, Septic,” and related keywords. The Newcastle-Ottawa scale was used for quality evaluation of the literature. A meta-analysis was performed using RevMan 5.3 and Stata 14.0 software to evaluate the effects of Pcv-aCO2/Ca-vO2 on short-term mortality, sequential organ failure assessment, and acute physiology and chronic health evaluation scores in patients with sepsis or septic shock.

Results:

The final analysis included 13 clinical studies involving a total of 940 subjects. The results of the meta-analysis showed that non-surviving patients had higher Pcv-aCO2/Ca-vO2 than survivors after fluid resuscitation (standardized mean difference = 0.68, 95% confidence interval = 0.24–1.12) and blood samples taken 6 h after resuscitation showed a greater risk of mortality (risk ratio = 1.89, 95% confidence interval = 1.48–2.41) and sequential organ failure assessment scores (mean difference = 1.58, 95% confidence interval = 0.88–2.28, P < 0.01) in patients with high Pcv-aCO2/Ca-vO2. These differences were statistically significant.

Conclusion:

This meta-analysis indicates that Pcv-aCO2/Ca-vO2 has predictive value for mortality in patients with sepsis or septic shock. Further studies are now required to determine the optimal threshold for predicting sepsis mortality.

Prospero Registration:

The protocol for this systematic review was registered on PROSPERO (CRD 42019128134).

Increased ratio of P[v-a]CO2 to C[a-v]O2 without global hypoxia: the case of metformin-induced lactic acidosis

The ratio of venoarterial CO₂ tension to arteriovenous O₂ content difference (P[v-a]CO₂/C[a-v]O₂) increases when lactic acidosis is due to inadequate oxygen supply (hypoxia); we aimed to verify whether it also increases when lactic acidosis develops because of mitochondrial dysfunction (dysoxia) with constant oxygen delivery. Twelve anaesthetised, mechanically ventilated pigs were intoxicated with IV metformin (4.0 to 6.4 g over 2.5 to 4.0 h). Saline and norepinephrine were used to preserve oxygen delivery. Lactate and P[v-a]CO₂/C[a-v]O₂ were measured every one or two hours (arterial and mixed venous blood). During metformin intoxication, lactate increased from 0.8 (0.6-0.9) to 8.5 (5.0-10.9) mmol/l (p < 0.001), even if oxygen delivery remained constant (from 352 ± 78 to 343 ± 97 ml/min, p = 0.098). P[v-a]CO₂/C[a-v]O₂ increased from 1.6 (1.2-1.8) to 2.3 (1.9-3.2) mmHg/ml/dl (p = 0.004). The intraclass correlation coefficient between lactate and P[v-a]CO₂/C[a-v]O₂ was 0.72 (p < 0.001). We conclude that P[v-a]CO₂/C[a-v]O₂ increases when lactic acidosis is due to dysoxia. Therefore, a high P[v-a]CO₂/C[a-v]O₂ may not discriminate hypoxia from dysoxia as the cause of lactic acidosis.

Prospective, observational study of carbon dioxide gaps and free energy change and their association with fluid therapy following cardiac surgery

Background Venoarterial carbon dioxide pressure (p_v-a CO₂ ) and content (C_v-a CO₂ ) differences, including the ratio to arteriovenous oxygen content difference (C_a-v O₂ ), and free energy changes (-∆∆G_a-v ) may reflect tissue hypoperfusion. The associations with changes in cardiac output (CO) or oxygen consumption (VO₂ ) following fluid bolus administration were investigated. Methods Single-centre, observational study of 89 adult post-operative cardiac surgical patients admitted to ICU. The p_v-a CO₂ , C_v-a CO₂ and their ratios to C_a-v O₂ as well as the -∆∆G_a-v were determined before and after a 250-500 mL fluid bolus using arterial, central venous and mixed venous blood gas analyses. Responses associated with changes ≥ or <15% in CO or oxygen consumption (VO₂ ) were compared. Results In 234 boluses, the mixed venous to arterial p_v-a CO₂ and its ratio to C_a-v O₂ were independently associated with an increase in CO; odds ratio 1.3 (95% CI 1.1-1.5) and 1.7 (95% CI 1.5-1.9) respectively, P < .001) and VO₂ ; odds ratio 2.1 (95% CI 1.3-3.1), P < .001 for C_a-v O₂ . No measures of p_v-a CO₂ , C_v-a CO₂ or related ratios to the C_a-v O₂ were associated with an increase in CO ≥15% following a single volume bolus. The mixed venous and central venous C_v-a CO₂ to C_a-v O₂ ratios were different for the first bolus episode only; mean differences 0.81 (95% CI 0.13-1.5), P = .02 and 0.44 (95% CI 0.06-0.82), P = .02, respectively, for increased VO₂  ≥ 15%. The -∆∆G_a-v did not change. Conclusion The venoarterial carbon dioxide gradients and related calculations to assess the adequacy of tissue perfusion before a fluid bolus were not associated with subsequent increases in CO of oxygen consumption. Editorial Comment In some shock conditions, regional tissue hypoperfusion can be obvious and arterio-venous differences for CO₂ or O₂ may reflect this. This is not always the case; sometimes there are A-V differences or even a high lactate level without any obvious regional tissue hypoperfusion. Fluid therapy is a cornerstone in shock resuscitation treatment, but determining optimal fluid therapy is challenging, particularly as fluid overload may be detrimental. Fluid challenges are used as an "ex juvantebus" method to dose fluid therapy, but it is not clear if a positive response reflects a state of hypoperfusion or the existence of a cardiac reserve. Still, a better understanding on how to target and guide fluid therapy is welcome, and studies digging into the problem are needed. Here, invasively monitored post-operative cardiac surgery patients are assessed as a model to investigate if carbon dioxide gaps and free energy charge may be useful in detecting possible tissue hypoperfusion.

Venous-to-arterial pCO2 difference in high-risk surgical patients

Alteration of tissue perfusion is a main contributor to organ dysfunction in high-risk surgical patients. The difference between venous carbon dioxide and arterial carbon dioxide pressure (pCO₂ gap) has been described as a parameter reflecting tissue hypoperfusion in critically ill patients who are insufficiently resuscitated. The pCO₂ gap/CavO₂ ratio has also been described as an indicator of the respiratory quotient, thus the relationship between DO₂ and VO₂. Most of the knowledge about the pCO₂ gap and the pCO₂ gap/CavO₂ ratio has come from studies in the literature on animal models or intensive care unit (ICU) patients. To date, publications pertaining to the operative setting are sparse. In the present review, we will first discuss the physiological background of the pCO₂ gap and CO₂-O₂ derived parameters used in the operating room. Few studies have focused on the clinical relevance of the pCO₂ gap in high-risk non-cardiac surgical patients. Prospective observational studies with a small sample size and retrospective studies have shown that the pCO₂ gap may be a useful complementary tool to identify patients who remain insufficiently optimized hemodynamically. In a few studies, a high pCO₂ gap was associated with postoperative complications following non-cardiac high-risk surgery. Results of observational studies conducted in patients undergoing cardiac surgery are contradictory. We focused on the divergence between non-cardiac surgery, cardiac surgery, and septic critically ill patients. When analyzing the literature, we can find some explanations for the discrepancies in the published results between cardiac and non-cardiac surgery. Finally, we will discuss the clinical utility of the pCO₂ gap in high-risk surgical patients.

P(v-a)CO2/C(a-v)O2-directed resuscitation does not improve prognosis compared with SvO2 in severe sepsis and septic shock: A prospective multicenter randomized controlled clinical study

PURPOSES

The present study examined the value of P(v-a)CO2/C(a-v)O2 compared with ScvO2 as a target for clinical resuscitation of severe sepsis/septic shock.

MATERIALS AND METHODS

228 patients were randomly divided into a P(v-a)CO2/C(a-v)O2-targeted and a ScvO2-targeted therapy group. The effects on hemodynamics, interventional intensity, and outcome were recorded and analyzed.

RESULTS

The mean arterial pressure (MAP) of the P(v-a)CO2/C(a-v)O2-targeted therapy group was significantly higher at 3 h, 12 h, 24 h, and 3 days (P < .05). The P(v-a)CO2/C(a-v)O2 of the ScvO2-targeted therapy group was significantly higher at each time point after resuscitation (P < .05). However, the CVP, lactate, urine output, ScvO2, and P(v-a)CO2 were not significantly improved. The P(v-a)CO2/C(a-v)O2-targeted therapy group used a smaller fluid volume and required fewer red blood cell transfusions and vasoactive drugs, but these results were also not significant. There were no differences between 28-day and 60-day mortality, APACHEII and SOFA scores, ICU length of stay, residence length of stay, number of days free of vasoactive drugs, or number of ventilator-free days. Post hoc tests revealed no significant differences between these two groups in 28-day survival.

CONCLUSION

P(v-a)CO2/C(a-v)O2-directed resuscitation did not improve prognosis compared with ScvO2 in severe sepsis and septic shock. ClinicalTrials.gov Identifier NCT01877798.