Central venous-arterial carbon dioxide difference as an indicator of cardiac index

Relationship between the mixed venous-to-arterial carbon dioxide gradient and the cardiac index in acute pulmonary embolism

AIMS

Among patients with acute pulmonary embolism (PE) undergoing mechanical thrombectomy, the cardiac index (CI) is frequently reduced even among those without a clinically apparent shock. The purpose of this study is to describe the mixed venous-to-arterial carbon dioxide gradient (CO2 gap), a surrogate of perfusion adequacy, among patients with acute PE undergoing mechanical thrombectomy.

METHODS AND RESULTS

This was a single-centre retrospective study of consecutive patients with PE undergoing mechanical thrombectomy and simultaneous pulmonary artery catheterization over a 3-year period. Of 107 patients, 97 had simultaneous mixed venous and arterial blood gas measurements available. The CO2 gap was elevated (>6 mmHg) in 51% of the cohort and in 49% of patients with intermediate-risk PE. A reduced CI (≤2.2 L/min/m2) was associated with an increased odds [odds ratio = 7.9; 95% confidence interval (CI) 3.49-18.1, P < 0.001] for an elevated CO2 gap. There was an inverse relationship between the CI and the CO2 gap. For every 1 L/min/m2 decrease in the CI, the CO2 gap increased by 1.3 mmHg (P = 0.001). Among patients with an elevated baseline CO2 gap >6 mmHg, thrombectomy improved the CO2 gap, CI, and mixed venous oxygen saturation. When the CO2 gap was dichotomized above and below 6, there was no difference in the in-hospital mortality rate (9 vs. 0%; P = 0.10; hazard ratio: 1.24; 95% CI 0.97-1.60; P = 0.085).

CONCLUSION

Among patients with acute PE undergoing mechanical thrombectomy, the CO2 gap is abnormal in nearly 50% of patients and inversely related to the CI. Further studies should examine the relationship between markers of perfusion and outcomes in this population to refine risk stratification.

Venous-to-arterial carbon-dioxide tension difference as a useful predictor of patient prognosis after major surgery

PURPOSE

Change in venous-to-arterial carbon dioxide partial pressure difference[P(v-a)CO2] could be a useful marker to assess tissue perfusion status. Herein, we assessed the predictive values of postoperative P(v-a)CO2 measurements for mortality in critically ill patients after major surgery. The correlation between P(v-a)CO2 values and other conventional parameters of patient prognosis was also evaluated.

METHODS

Patients admitted to the intensive care unit(ICU) after abdominal surgery were enrolled. Arterial and venous blood gas analyses were performed within 1 h(T0) and after 24 h(T1) of admission to the ICU, respectively. The relationship between P(v-a)CO2 levels at T1 and other conventional parameters were assessed using a Bland-Altman plot. Logistic regression analysis was performed to examine the predisposing factors of mortality after surgery.

RESULTS

A total of 231 patients were finally analyzed. We divided the participants into the high PvaCO2 group[P(v-a)CO2 ≥ 8.6] and the low PvaCO2 group[P(v-a)CO2 < 8.6]. Seven-day-, 28-day, and in-hospital mortality were significantly higher in the high PvaCO2 group than in the low PvaCO2 group. There was significant agreement between P(v-a)CO2 values at T1 and APACHE II scores, lactate levels at T1 and total SOFA scores at T1. In multivariate logistic analysis, an increased P(v-a)CO2 value at T1 was the only significant risk factor of 7-day mortality after surgery. [odds ratio:1.341, 95%confidence interval: 1.050-1.714, p=0.019].

CONCLUSION

P(v-a)CO2 measurements could be not only a significant predictor of postoperative prognosis, but also a useful surveillance parameter to maintain tissue perfusion after abdominal surgery in patients with a potential risk of fatal complication-related tissue hypoperfusion.

The Evolution of Central Venous-to-arterial Carbon Dioxide Difference (PCO2 Gap) during Resuscitation Affects ICU Outcomes: A Prospective Observational Study

Introduction

The usual methods of perfusion assessment in patients with shock, such as capillary refill time, skin mottling, and serial serum lactate measurements have many limitations. Veno-arterial difference in the partial pressure of carbon dioxide (PCO2 gap) is advocated being more reliable. We evaluated serial change in PCO2 gap during resuscitation in circulatory shock and its effect on ICU outcomes.

Materials and methods

This prospective observational study included 110 adults with circulatory shock. Patients were resuscitated as per current standards of care. We recorded invasive arterial pressure, urine output, cardiac index (CI), PCO2 gap at ICU admission at 6, 12, and 24 hours, and various patient outcomes.

Results

Significant decrease in PCO2 gap was observed at 6 h and was accompanied by improvement in serum lactate, mean arterial pressure, CI and urine output in (n = 61). We compared these patients with those in whom this decrease did not occur (n = 49). Mortality and ICU LOS was significantly lower in patients with low PCO2 gap, while more patients with high PCO2 gap required RRT.

Conclusion

We found that a persistently high PCO2 gap at 6 and 12 h following resuscitation in patients with shock of various etiologies, was associated with increased mortality, need for RRT and increased ICU LOS. High PCO2 gap had a moderate discriminative ability to predict mortality.

How to cite this article

Zirpe KG, Tiwari AM, Kulkarni AP, Vaidya HS, Gurav SK, Deshmukh AM, et al. The Evolution of Central Venous-to-arterial Carbon Dioxide Difference (PCO2 Gap) during Resuscitation Affects ICU Outcomes: A Prospective Observational Study. Indian J Crit Care Med 2024;28(4):349-354.

EXPLORING THE ROLE OF CENTRAL VENOUS OXYGEN SATURATION IN THE EVALUATION AND MANAGEMENT OF SEVERE HYPOXEMIA IN MECHANICALLY VENTILATED PATIENTS

ABSTRACT

Background: Although central venous oxygen saturation (ScvO 2 ) has been used as an endpoint for the treatment of circulatory shock, its role in guiding the evaluation and treatment of patients with severe hypoxemia remains to be assessed. The aim of this study was to assess the incidence of low ScvO 2 in a cohort of hypoxemic patients and the association of this finding with differences in clinical management and patient outcomes. Methods: Retrospective review of data from adult intensive care unit patients with hypoxemia who required invasive mechanical ventilation for over 24 h and had at least one ScvO 2 measured within 6 h of a PaO 2 /FiO 2 ratio <200. Results: Of 442 mechanically ventilated patients with severe hypoxemia, 249 (56%) had an ScvO 2 <70%. When compared with patients with ScvO 2 ≥70%, those with low ScvO 2 had worse systemic oxygenation and hemodynamic parameters and were more likely to receive red blood cell transfusions (31.7% vs. 18.1%, P = 0.001), epinephrine (27.3% vs. 16.6%, P = 0.007), and inodilators. Outcomes such as median intensive care unit length of stay (7.5 vs. 8.3 days, P = 0.337) and hospital mortality (39.8% vs. 35.7%, P = 0.389) were not different between groups. When stratified by the central venous-to-arterial CO 2 difference (∆PCO 2 ), patients with a low ScvO 2 and normal ∆PCO 2 had lower median PaO 2 and hemoglobin levels and received more red blood cell transfusions, whereas those with an increased ∆PCO 2 had a lower pulse pressure and cardiac index and were more likely to receive epinephrine and milrinone. Conclusion: Low ScvO 2 is frequently observed in mechanically ventilated patients with severe hypoxemia, and these patients receive different interventions. Clinicians often use therapies targeting systemic oxygen delivery to correct low ScvO 2 . Prospective research is needed to identify patients with severe hypoxemia that might benefit from interventions targeting systemic oxygen delivery.

Subclinical cardiac dysfunction may impact on fluid and vasopressor administration during early resuscitation of septic shock

BACKGROUND

According to the Surviving Sepsis Campaign (SSC) fluids and vasopressors are the mainstays of early resuscitation of septic shock while inotropes are indicated in case of tissue hypoperfusion refractory to fluids and vasopressors, suggesting severe cardiac dysfunction. However, septic cardiac disfunction encompasses a large spectrum of severities and may remain "subclinical" during early resuscitation. We hypothesized that "subclinical" cardiac dysfunction may nevertheless influence fluid and vasopressor administration during early resuscitation. We retrospectively reviewed prospectically collected data on fluids and vasoconstrictors administered outside the ICU in patients with septic shock resuscitated according to the SSC guidelines that had reached hemodynamic stability without the use of inotropes. All the patients were submitted to transpulmonary thermodilution (TPTD) hemodynamic monitoring at ICU entry. Subclinical cardiac dysfunction was defined as a TPTD-derived cardiac function index (CFI) ≤ 4.5 min-1.

RESULTS

At ICU admission, subclinical cardiac dysfunction was present in 17/40 patients (42%; CFI 3.6 ± 0.7 min-1 vs 6.6 ± 1.9 min-1; p < 0.01). Compared with patients with normal CFI, these patients had been resuscitate with more fluids (crystalloids 57 ± 10 vs 47 ± 9 ml/kg PBW; p < 0.01) and vasopressors (norepinephrine 0.65 ± 0.25 vs 0.43 ± 0.29 mcg/kg/min; p < 0.05). At ICU admission these patients had lower cardiac index (2.2 ± 0.6 vs 3.6 ± 0.9 L/min/m2, p < 0.01) and higher systemic vascular resistances (2721 ± 860 vs 1532 ± 480 dyn*s*cm-5/m2, p < 0.01).

CONCLUSIONS

In patients with septic shock resuscitated according to the SSC, we found that subclinical cardiac dysfunction may influence the approach to fluids and vasopressor administration during early resuscitation. Our data support the implementation of early, bedside assessment of cardiac function during early resuscitation of septic shock.

Venous Minus Arterial Carbon Dioxide Gradients in the Monitoring of Tissue Perfusion and Oxygenation: A Narrative Review

According to Fick's principle, the total uptake of (or release of) a substance by tissues is the product of blood flow and the difference between the arterial and the venous concentration of the substance. Therefore, the mixed or central venous minus arterial CO₂ content difference depends on cardiac output (CO). Assuming a linear relationship between CO₂ content and partial pressure, central or mixed venous minus arterial PCO₂ differences (P_cv-aCO₂ and P_mv-aCO₂) are directly related to CO. Nevertheless, this relationship is affected by alterations in the CO₂Hb dissociation curve induced by metabolic acidosis, hemodilution, the Haldane effect, and changes in CO₂ production (VCO₂). In addition, P_cv-aCO₂ and P_mv-aCO₂ are not interchangeable. Despite these confounders, CO is a main determinant of P_cv-aCO₂. Since in a study performed in septic shock patients, P_mv-aCO₂ was correlated with changes in sublingual microcirculation but not with those in CO, it has been proposed as a monitor for microcirculation. The respiratory quotient (RQ)-RQ = VCO₂/O₂ consumption-sharply increases in anaerobic situations induced by exercise or critical reductions in O₂ transport. This results from anaerobic VCO₂ secondary to bicarbonate buffering of anaerobically generated protons. The measurement of RQ requires expired gas analysis by a metabolic cart, which is not usually available. Thus, some studies have suggested that the ratio of P_cv-aCO₂ to arterial minus central venous O₂ content (P_cv-aCO₂/C_a-cvO₂) might be a surrogate for RQ and tissue oxygenation. In this review, we analyze the physiologic determinants of P_cv-aCO₂ and P_cv-aCO₂/C_a-cvO₂ and their potential usefulness and limitations for the monitoring of critically ill patients. We discuss compelling evidence showing that they are misleading surrogates for tissue perfusion and oxygenation, mainly because they are systemic variables that fail to track regional changes. In addition, they are strongly dependent on changes in the CO₂Hb dissociation curve, regardless of changes in systemic and microvascular perfusion and oxygenation.

Femoral blood gas analysis, another tool to assess hemorrhage severity following trauma: an exploratory prospective study

BACKGROUND

Veno-arterial carbon dioxide tension difference (ΔPCO2) and mixed venous oxygen saturation (SvO2) have been shown to be markers of the adequacy between cardiac output and metabolic needs in critical care patients. However, they have hardly been assessed in trauma patients. We hypothesized that femoral ΔPCO2 (ΔPCO2 fem) and SvO2 (SvO2 fem) could predict the need for red blood cell (RBC) transfusion following severe trauma.

METHODS

We conducted a prospective and observational study in a French level I trauma center. Patients admitted to the trauma room following severe trauma with an Injury Severity Score (ISS) > 15, who had arterial and venous femoral catheters inserted were included. ΔPCO2 fem, SvO2 fem and arterial blood lactate were measured over the first 24 h of admission. Their abilities to predict the transfusion of at least one pack of RBC (pRBCH6) or hemostatic procedure during the first six hours of admission were assessed using receiver operating characteristics curve.

RESULTS

59 trauma patients were included in the study. Median ISS was 26 (22-32). 28 patients (47%) received at least one pRBCH6 and 21 patients (35,6%) had a hemostatic procedure performed during the first six hours of admission. At admission, ΔPCO2 fem was 9.1 ± 6.0 mmHg, SvO2 fem 61.5 ± 21.6% and blood lactate was 2.7 ± 1.9 mmol/l. ΔPCO2 fem was significantly higher (11.6 ± 7.1 mmHg vs. 6.8 ± 3.7 mmHg, P = 0.003) and SvO2 fem was significantly lower (50 ± 23 mmHg vs. 71.8 ± 14.1 mmHg, P < 0.001) in patients who were transfused than in those who were not transfused. Best thresholds to predict pRBCH6 were 8.1 mmHg for ΔPCO2 fem and 63% for SvO2 fem. Best thresholds to predict the need for a hemostatic procedure were 5.9 mmHg for ΔPCO2 fem and 63% for SvO2 fem. Blood lactate was not predictive of pRBCH6 or the need for a hemostatic procedure.

CONCLUSION

In severe trauma patients, ΔPCO2 fem and SvO2 fem at admission were predictive for the need of RBC transfusion and hemostatic procedures during the first six hours of management while admission lactate was not. ΔPCO2 fem and SvO2 fem appear thus to be more sensitive to blood loss than blood lactate in trauma patients, which might be of importance to early assess the adequation of tissue blood flow with metabolic needs.

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.

Veno-arterial CO2 difference and lactate for prediction of early mortality after cardiac arrest

Patients admitted to intensive care after cardiac arrest are at risk of circulatory shock and early mortality due to cardiovascular failure. The aim of this study was to evaluate the ability of the veno-arterial pCO₂ difference (∆pCO₂ ; central venous CO₂ - arterial CO₂ ) and lactate to predict early mortality in postcardiac arrest patients. This was a pre-planned prospective observational sub-study of the target temperature management 2 trial. The sub-study patients were included at five Swedish sites. Repeated measurements of ∆pCO₂ and lactate were conducted at 4, 8, 12, 16, 24, 48, and 72 h after randomization. We assessed the association between each marker and 96-h mortality and their prognostic value for 96-h mortality. One hundred sixty-three patients were included in the analysis. Mortality at 96 h was 17%. During the initial 24 h, there was no difference in ∆pCO₂ levels between 96-h survivors and non-survivors. ∆pCO₂ measured at 4 h was associated with an increased risk of death within 96 h (adjusted odds ratio: 1.15; 95% confidence interval [CI]: 1.02-1.29; p = .018). Lactate levels were associated with poor outcome over multiple measurements. The area under the receiving operating curve to predict death within 96 h was 0.59 (95% CI: 0.48-0.74) and 0.82 (95% CI: 0.72-0.92) for ∆pCO₂ and lactate, respectively. Our results do not support the use of ∆pCO₂ to identify patients with early mortality in the postresuscitation phase. In contrast, non-survivors demonstrated higher lactate levels in the initial phase and lactate identified patients with early mortality with moderate accuracy.

Does veno-arterial carbon dioxide gradient provide an adequate estimation of cardiac index in pulmonary hypertension?

AIMS

Pulmonary hypertension (PH) management is dependent on cardiac output (CO) assessment. The gold standard Fick method for CO and cardiac index (CI) measurement is not widely available. An accessible and reliable method for CO/CI estimation is needed not only in catheterization labs but also in other environments such as the intensive care unit, where pulmonary artery catheters are less likely to be used. We hypothesized that veno-arterial carbon dioxide gradient (PvaCO2) is a reliable surrogate for Fick CI in patients with PH.

METHODS AND RESULTS

A single-centre retrospective analysis of patients with PH who underwent direct Fick CI (DFCI) measurement during right heart catheterization. The primary outcome was correlation between PvaCO2 and DFCI. To assess the agreement between central and mixed venous CO2 values, a separate prospective cohort of patients was analysed. Data from 186 patients with all haemodynamic types of PH were analysed. PvaCO2 moderately correlated with Fick CI, R = -0.51 [95% confidence interval (CI): -0.61, -0.39]. A higher PvaCO2 was associated with an increased risk of CI < 2.5 L/min/m2 (odds ratio: 1.88, 95% CI: 1.55, 2.35). Low thermodilution CI with normal veno-arterial carbon dioxide gradient values was associated with a thermodilution underestimation of Fick CI. In the prospective analysis of 32 patients, central venous CO2 overestimated mixed venous values (mean difference 3.3, 95% CI: 2.5, 4.0) and there was poor agreement overall (limits of agreement -1.10, 7.59).

CONCLUSION

Veno-arterial carbon dioxide gradient moderately correlates with Fick CI and may be useful to identify patients with low CI. Central and mixed venous CO2 values should not be used interchangeably in PH.

Pathophysiology of fluid administration in critically ill patients

Fluid administration is a cornerstone of treatment of critically ill patients. The aim of this review is to reappraise the pathophysiology of fluid therapy, considering the mechanisms related to the interplay of flow and pressure variables, the systemic response to the shock syndrome, the effects of different types of fluids administered and the concept of preload dependency responsiveness. In this context, the relationship between preload, stroke volume (SV) and fluid administration is that the volume infused has to be large enough to increase the driving pressure for venous return, and that the resulting increase in end-diastolic volume produces an increase in SV only if both ventricles are operating on the steep part of the curve. As a consequence, fluids should be given as drugs and, accordingly, the dose and the rate of administration impact on the final outcome. Titrating fluid therapy in terms of overall volume infused but also considering the type of fluid used is a key component of fluid resuscitation. A single, reliable, and feasible physiological or biochemical parameter to define the balance between the changes in SV and oxygen delivery (i.e., coupling "macro" and "micro" circulation) is still not available, making the diagnosis of acute circulatory dysfunction primarily clinical.

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.

Central Venous-to-Arterial CO2 Difference-Assisted Goal-Directed Hemodynamic Management During Major Surgery-A Randomized Controlled Trial

BACKGROUND

Different goals have guided goal-directed therapy (GDT). Protocols aiming for central venous-to-arterial carbon dioxide gap (DCO2) <6 mm Hg have improved organ function in septic shock. Evidence for use of DCO2 in the perioperative period is scarce. We aimed to determine if a GDT protocol using central venous saturation of oxygen (SCvo2) and DCO2 reduced organ dysfunction and intensive care unit (ICU) stay in American Society of Anesthesiologist (ASA) I and II patients undergoing major surgeries compared to pragmatic goal-directed care.

METHODS

One hundred patients were randomized. Arterial and venous blood-gas values were recorded every 2 hours perioperatively for all patients. Intervention group (GrI) with access to both values was managed per protocol based on DCO2 and SCvo2. Dobutamine infusion 3 to 5 µg/kg/min started if DCO2 >6 mm Hg after correcting all macrocirculatory end points. Control group (GrC) had access only to arterial-gas values and managed per "conventional" goals without DCO2 or SCvo2. Patients were followed for 48 hours after surgery. Organ dysfunction, sequential organ failure assessment (SOFA) scores-primary outcome, length of stay in ICU, and duration of postoperative mechanical ventilation and hospital stay were recorded. The patient, surgeons, ICU team, and analyzer were blinded to group allocation.

RESULTS

The groups (44 each) did not significantly differ with respect to baseline characteristics. Perioperative fluids, blood products, and vasopressors used did not significantly differ. The GrI had less organ dysfunction although not significant (79% vs 66%; P = .2). Length of ICU stay in the GrI was significantly less (1.52; standard deviation [SD], 0.82 vs 2.18; SD, 1.08 days; P = .002). Mechanical ventilation duration (0.9 days in intervention versus 0.6 days in control; P = .06) and length of hospital stay did not significantly differ between the groups. Perioperative DCO2 (5.8 vs 8.4 mm Hg; P < .001) and SCvo2 (73.5 vs 68.4 mm Hg; P < .001) were significantly better in the GrI.

CONCLUSIONS

GDT guided by DCO2 did not improve organ function in our cohort. It resulted in greater use of dobutamine, improved tissue oxygen parameters, and decreased length of ICU stay. More evidence is needed for the routine use of DCO2 in sicker patients. In the absence of cardiac output monitors, it may be a readily available, less-expensive, and underutilized parameter for major surgical procedures.

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.

Central venous-to-arterial PCO2 difference as a marker to identify fluid responsiveness in septic shock

Defining the hemodynamic response to volume therapy is integral to managing critically ill patients with acute circulatory failure, especially in the absence of cardiac index (CI) measurement. This study aimed at investigating whether changes in central venous-to-arterial CO₂ difference (Δ-ΔPCO₂) and central venous oxygen saturation (ΔScvO₂) induced by volume expansion (VE) are reliable parameters to define fluid responsiveness in sedated and mechanically ventilated septic patients. We prospectively studied 49 critically ill septic patients in whom VE was indicated because of circulatory failure and clinical indices. CI, ΔPCO₂, ScvO₂, and oxygen consumption (VO₂) were measured before and after VE. Responders were defined as patients with a > 10% increase in CI (transpulmonary thermodilution) after VE. We calculated areas under the receiver operating characteristic curves (AUCs) for Δ-ΔPCO₂, ΔScvO₂, and changes in CI (ΔCI) after VE in the whole population and in the subgroup of patients with an increase in VO₂ (ΔVO₂) ≤ 10% after VE (oxygen-supply independency). Twenty-five patients were fluid responders. In the whole population, Δ-ΔPCO₂ and ΔScvO₂ were significantly correlated with ΔCI after VE (r =  − 0.30, p = 0.03 and r = 0.42, p = 0.003, respectively). The AUCs for Δ-ΔPCO₂ and ΔScvO₂ to define fluid responsiveness (increase in CI > 10% after VE) were 0.76 (p < 0.001) and 0.68 (p = 0.02), respectively. In patients with ΔVO₂ ≤ 10% (n = 36) after VE, the correlation between ΔScvO₂ and ΔCI was 0.62 (p < 0.001), and between Δ-ΔPCO₂ and ΔCI was − 0.47 (p = 0.004). The AUCs for Δ-ΔPCO₂ and ΔScvO₂ were 0.83 (p < 0.001) and 0.73 (p = 0.006), respectively. In these patients, Δ-ΔPCO₂ ≤ -37.5% after VE allowed the categorization between responders and non-responders with a positive predictive value of 100% and a negative predictive value of 60%. In sedated and mechanically ventilated septic patients with no signs of tissue hypoxia (oxygen-supply independency), Δ-ΔPCO₂ is a reliable parameter to define fluid responsiveness.

The Use of Central Venous to Arterial Carbon Dioxide Tension Gap for Outcome Prediction in Critically Ill Patients: A Systematic Review and Meta-Analysis

OBJECTIVES

In this systematic review and meta-analysis, we assessed whether a high CO2 gap predicts mortality in adult critically ill patients with circulatory shock.

DATA SOURCES

A systematic search of MEDLINE and EMBASE electronic databases from inception to October 2019.

STUDY SELECTION

Studies from adult (age ≥ 18 yr) ICU patients with shock reporting CO2 gap and outcomes of interest. Case reports and conference abstracts were excluded.

DATA EXTRACTION

Data extraction and study quality assessment were performed independently in duplicate.

DATA SYNTHESIS

We used the Newcastle-Ottawa Scale to assess methodological study quality. Effect sizes were pooled using a random-effects model. The primary outcome was mortality (28 d and hospital). Secondary outcomes were ICU length of stay, hospital length of stay, duration of mechanical ventilation, use of renal replacement therapy, use of vasopressors and inotropes, and association with cardiac index, lactate, and central venous oxygen saturation.

CONCLUSIONS

We included 21 studies (n = 2,155 patients) from medical (n = 925), cardiovascular (n = 685), surgical (n = 483), and mixed (n = 62) ICUs. A high CO2 gap was associated with increased mortality (odds ratio, 2.22; 95% CI, 1.30-3.82; p = 0.004) in patients with shock, but only those from medical and surgical ICUs. A high CO2 gap was associated with higher lactate levels (mean difference 0.44 mmol/L; 95% CI, 0.20-0.68 mmol/L; p = 0.0004), lower cardiac index (mean difference, -0.76 L/min/m; 95% CI, -1.04 to -0.49 L/min/m; p = 0.00001), and central venous oxygen saturation (mean difference, -5.07; 95% CI, -7.78 to -2.37; p = 0.0002). A high CO2 gap was not associated with longer ICU or hospital length of stays, requirement for renal replacement therapy, longer duration of mechanical ventilation, or higher vasopressors and inotropes use. Future studies should evaluate whether resuscitation aimed at closing the CO2 gap improves mortality in shock.

Central Venous-to-Arterial PCO2 Difference and Central Venous Oxygen Saturation in the Detection of Extubation Failure in Critically Ill Patients

OBJECTIVES

To evaluate the ability of central venous-to-arterial carbon dioxide pressure difference, central venous oxygen saturation, and the combination of these two parameters to detect extubation failure in critically ill patients.

DESIGN

Multicentric, prospective, observational study.

SETTING

Three ICUs.

PATIENTS

All patients who received mechanical ventilation for more than 48 hours and tolerated spontaneous breathing trials with a T-piece for 60 minutes.

INTERVENTIONS

Extubation after successful spontaneous breathing trials. Extubation failure was defined as the need for mechanical ventilation within 48 hours.

MEASUREMENTS AND MAIN RESULTS

The oxygen delivery index, oxygen consumption index, central venous oxygen saturation, central venous-to-arterial carbon dioxide pressure difference, and oxygen extraction were measured immediately before spontaneous breathing trials and at 60 minutes after spontaneous breathing trials initiation. Seventy-five patients were enrolled, and extubation failure was noted in 18 (24%) patients. Oxygen consumption index increased significantly during spontaneous breathing trials in the failure group. Oxygen delivery index increased in both success and failure groups. Oxygen extraction increased in the failure group (p = 0.005) and decreased in the success group (p = 0.001). Central venous oxygen saturation decreased in the failure group and increased in the success group (p = 0.014). ΔPCO2 value increased in the extubation failure group and decreased in the success group (p = 0.002). Changes in ΔPCO2 (Δ - ΔPCO2) and central venous oxygen saturation (ΔScvO2) during spontaneous breathing trials were independently associated with extubation failure (odds ratio, 1.02; 95% CI, 1.01-1.05; p = 0.006, and odds ratio, 0.84; 95% CI, 0.70-0.95; p = 0.02, respectively). Δ - ΔPCO2 and central venous oxygen saturation could predict extubation failure with areas under the curve of 0.865 and 0.856, respectively; however, their combined areas under the curve was better at 0.940.

CONCLUSIONS

We found that Δ - ΔPCO2 and central venous oxygen saturation, during spontaneous breathing trials, were independent predictors of weaning outcomes. Combination analysis of both parameters enhanced their diagnostic performance and provided excellent predictability in extubation failure detection in critically ill patients.

Changes in perfusion can detect changes in the cardiac index in patients with septic shock

Objective

The perfusion index (PI) is usually used to assess peripheral perfusion, which can be influenced by the cardiac index (CI). CI monitoring is often needed during the treatment of patients with shock. We investigated the relationship between changes in the PI (ΔPI) and changes in the CI (ΔCI) in patients with septic shock.

Methods

This retrospective study included patients with septic shock who underwent pulse-induced continuous cardiac output monitoring. We measured the CI and PI before and after fluid loading during the first 6 hours of intensive care unit admission. Fluid responsiveness was defined as a ≥10% ΔCI after fluid loading. Other hemodynamic and oxygen-derived parameters were also collected at the exact time of each CI measurement.

Results

Fifty-five patients were included in the study (29 fluid responders, 26 fluid non-responders). In the univariate analysis, ΔPI was positively correlated with ΔCI. In the multivariable analysis, ΔPI was independently associated with ΔCI. The receiver operating characteristic curve showed that ΔPI was an appropriate marker with which to discriminate a CI increase with an area under the curve of 0.776.

Conclusion

This study showed a positive correlation between ΔPI and ΔCI during the early treatment phase of septic shock.

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.

Central venous-to-arterial CO2 difference is a poor tool to predict adverse outcomes after cardiac surgery: a retrospective study

PURPOSE

The venous-to-arterial carbon dioxide partial pressure difference (CO₂ gap) has been reported to be a sensitive indicator of cardiac output adequacy. We aimed to assess whether the CO₂ gap can predict postoperative adverse outcomes after cardiac surgery.

METHODS

A retrospective study was conducted of 5,151 patients from our departmental database who underwent cardiac surgery from 1 January 2008 to 31 December 2018. Lactate level (mmol·L^-1), central venous oxygen saturation (ScVO₂) (%), and the venous-to-arterial carbon dioxide difference (CO₂ gap) were measured at intensive care unit (ICU) admission and on days 1 and 2 after cardiac surgery. The following postoperative adverse outcomes were collected: ICU mortality, hemopericardium or tamponade, resuscitated cardiac arrest, acute kidney injury, major bleeding, acute hepatic failure, mesenteric ischemia, and pneumonia. The primary outcome was the presence of at least one postoperative adverse outcome. Logistic regression was used to assess the association between ScVO₂, lactate, and the CO₂ gap with adverse outcomes. Their diagnostic performance was compared using a receiver operating characteristic (ROC) curve.

RESULTS

There were 1,933 patients (38%) with an adverse outcome. Cardiopulmonary bypass (CPB) parameters were similar between groups. The CO₂ gap was slightly higher for the "adverse outcomes" group than for the "no adverse outcomes" group. Arterial lactate at admission, day 1, and day 2 was also slightly higher in patients with adverse outcomes. Central venous oxygen saturation was not significantly different between patients with and without adverse outcomes. The area under the ROC curve to predict outcomes after CPB for the CO₂ gap at admission, day 1, and day 2 were 0.52, 0.55, and 0.53, respectively.

CONCLUSION

After cardiac surgery with CPB, the CO₂ gap at ICU admission, day 1, and day 2 was associated with postoperative adverse outcomes but showed poor diagnostic performance.

Biochemical markers for clinical monitoring of tissue perfusion

The assessment and monitoring of the tissue perfusion is extremely important in critical conditions involving circulatory shock. There is a wide range of established methods for the assessment of cardiac output as a surrogate of oxygen delivery to the peripheral tissues. However, the evaluation of whether particular oxygen delivery is sufficient to ensure cellular metabolic demands is more challenging. In recent years, specific biochemical parameters have been described to indicate the status between tissue oxygen demands and supply. In this review, the authors summarize the application of some of these biochemical markers, including mixed venous oxygen saturation (S_vO₂), lactate, central venous–arterial carbon dioxide difference (PCO₂ gap), and PCO₂ gap/central arterial-to-venous oxygen difference (C_a–vO₂) for hemodynamic assessment of tissue perfusion. The thorough monitoring of the adequacy of tissue perfusion and oxygen supply in critical conditions is essential for the selection of the most appropriate therapeutic strategy and it is associated with improved clinical outcomes.

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.

The relationship between inotropic support therapy and central partial pressure of venous-arterial carbon dioxide after cardiopulmonary bypass

Background

This study aims to investigate the effects of partial pressure of venous-arterial carbon dioxide changes in the early period after cardiopulmonary bypass in patients who did or did not receive inotropic support therapy and the effect of these changes on tissue perfusion.

Methods

A total of 100 consecutive patients (70 males, 30 females; mean age 61.8±2.3 years; range, 20 to 75 years) who underwent open heart surgery were divided into two groups as those who did not receive any inotropic agent (group 1, n=50) and those who received at least one inotropic agent (group 2, n=50) during the early postoperative period. Heart rate, blood oxygen saturation level, mean arterial pressure, central venous pressure and urine volume, lactate and base excess levels were recorded during the postoperative first 24 hours. At the same timeframe, partial pressure of venous-arterial carbon dioxide level was calculated from central venous and peripheral blood samples.

Results

In both groups, partial pressure of venous-arterial carbon dioxide were significantly higher in the postoperative fourth hour compared with basal values. This significant difference continued for the postoperative first 24 hours. Partial pressure of venous-arterial carbon dioxide in group 2 was significantly higher at the 12^th-hour measurement (p=0.002). Lactate levels at zeroth and eighth hours were significantly higher in group 2 (p=0.012 and p=0.017, respectively). Fourthhour urine excretion volumes were significantly lower in group 1 (p=0.010). Mean arterial pressure at zeroth, 12th and 20th hours was significantly higher in group 2 (p=0.001, p=0.016, and p=0.027, respectively). At the eighth-hour measurement, a positive weak relationship was detected between partial pressure of venousarterial carbon dioxide and lactate levels (r=0.253 and p=0.033).

Conclusion

This study demonstrated that partial pressure of venous-arterial carbon dioxide increased in the first few hours and remained to be high for 24 hours after cardiopulmonary bypass independently of the use of inotropic support. However, in the postoperative period, even after lactate and base excess levels return to baseline values, partial pressure of venous-arterial carbon dioxide may continue to remain at high values, which may indicate impaired perfusion in some tissues.

The Forgotten Hemodynamic (PCO2 Gap) in Severe Sepsis

Background

Central venous-arterial carbon dioxide difference (PCO2 gap) can be a marker of cardiac output adequacy in global metabolic conditions that are less affected by the impairment of oxygen extraction capacity. We investigated the relation between the PCO2 gap, serum lactate, and cardiac index (CI) and prognostic value on admission in relation to fluid administration in the early phases of resuscitation in sepsis. We also investigated the chest ultrasound pattern A or B.

Method

We performed a prospective observational study and recruited 28 patients with severe sepsis and septic shock in a mixed ICU. We determined central venous PO2, PCO2, PCO2 gap, lactate, and CI at 0 and 6 hours after critical care unit (CCU) admission. The population was divided into two groups based on the PCO2 gap (cutoff value 0.8 kPa).

Results

The CI was significantly lower in the high PCO2 gap group (P=0.001). The high PCO2 gap group, on admission, required more administered fluid and vasopressors (P=0.01 and P=0.009, respectively). There was also a significant difference between the two groups for low mean pressure (P=0.01), central venous O2 (P=0.01), and lactate level (P=0.003). The mean arterial pressure was lower in the high PCO2 gap group, and the lactate level was higher, indicating global hypoperfusion. The hospital mortality rate for all patients was 24.5% (7/28). The in-hospital mortality rate was 20% (2/12) for the low gap group and 30% (5/16) for the high gap group; the odds ratio was 1.6 (95% CI 0.5–5.5; P=0.53). Patients with a persistent or rising PCO2 gap larger than 0.8 kPa at T = 6 and 12 hours had a higher mortality change (n = 6; in-hospital mortality was 21.4%) than patients with a PCO2 gap of less than 0.8 kPa at T = 6 (n = 1; in-hospital mortality was 3%); this odds ratio was 5.3 (95% CI 0.9–30.7; P=0.08). The PCO2 gap had no relation with the chest ultrasound pattern.

Conclusion

The PCO2 gap is an important hemodynamic variable in the management of sepsis-induced circulatory failure. The PCO2 gap can be a marker of the adequacy of the cardiac output status in severe sepsis. A high PCO2 gap value (>0.8 kPa) can identify situations in which increasing CO can be attempted with fluid resuscitation in severe sepsis. The PCO2 gap carries an important prognostic value in severe sepsis.

Using pCO2 Gap in the Differential Diagnosis of Hyperlactatemia Outside the Context of Sepsis: A Physiological Review and Case Series

INTRODUCTION

There is an inverse relationship between cardiac output and the central venous-arterial difference of partial pressures of carbon dioxide (pCO2 gap), and pCO2 gap has been used to guide early resuscitation of septic shock. It can be hypothesized that pCO2 gap can be used outside the context of sepsis to distinguish type A and type B lactic acidosis and thereby avoid unnecessary fluid resuscitation in patients with high lactate, but without organ hypoperfusion.

METHODS

We performed a structured review of the literature enlightening the physiological background. Next, we retrospectively selected a series of case reports of nonseptic critically ill patients with elevated lactate, in whom both arterial and central venous blood gases were simultaneously measured and the diagnosis of either type A or type B hyperlactataemia was conclusively known. In these cases, we calculated venous-arterial CO2 and O2 content differences and pCO2 gap.

RESULTS

Based on available physiological data, pCO2 can be considered as an acceptable surrogate of venous-arterial CO2 content difference, and it should better reflect cardiac output than central venous saturation or indices based on venous-arterial O2 content difference. In our case report of nonseptic patients, we observed that if global hypoperfusion was present (i.e., in type A lactic acidosis), pCO2 gap was elevated (>1 kPa), whilst in the absence of it (i.e., in type B lactic acidosis), pCO2 gap was low (<0.5 kPa).

CONCLUSION

Physiological rationale and a small case series are consistent with the hypothesis that low pCO2 gap in nonseptic critically ill is suggestive of the absence of tissue hypoperfusion, mandating the search for the cause of type B lactic acidosis rather than administration of fluids or other drugs aimed at increasing cardiac output.

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.

Mystery of PCO2 Gap in Sepsis

How to cite this article: Patil VP. Mystery of PCO2 Gap in Sepsis. Indian J Crit Care Med 2019;23(10):443-444.

Improving the prognostic value of ∆PCO2 following cardiac surgery: a prospective pilot study

Conflicting results have been published on prognostic significance of central venous to arterial PCO₂ difference (∆PCO₂) after cardiac surgery. We compared the prognostic value of ∆PCO₂ on intensive care unit (ICU) admission to an original algorithm combining ∆PCO₂, ERO₂ and lactate to identify different risk profiles. Additionally, we described the evolution of ∆PCO₂ and its correlations with ERO₂ and lactate during the first postoperative day (POD1). In this monocentre, prospective, and pilot study, 25 patients undergoing conventional cardiac surgery were included. Central venous and arterial blood gases were collected on ICU admission and at 6, 12 and 24 h postoperatively. High ∆PCO₂ (≥ 6 mmHg) on ICU admission was found to be very frequent (64% of patients). Correlations between ∆PCO₂ and ERO₂ or lactate for POD1 values and variations were weak or non-existent. On ICU admission, a high ∆PCO₂ did not predict a prolonged ICU length of stay (LOS). Conversely, a significant increase in both ICU and hospital LOS was observed in high-risk patients identified by the algorithm: 3.5 (3.0–6.3) days versus 7.0 (6.0–8.0) days (p = 0.01) and 12.0 (8.0–15.0) versus 8.0 (8.0–9.0) days (p < 0.01), respectively. An algorithm incorporating ICU admission values of ∆PCO₂, ERO₂ and lactate defined a high-risk profile that predicted prolonged ICU and hospital stays better than ∆PCO₂ alone.

Interpretation of venous-to-arterial carbon dioxide difference in the resuscitation of septic shock patients

The venous-to-arterial carbon dioxide difference [P(v-a)CO₂] was calculated from the difference of venous CO₂ and arterial CO₂, which has been used to reflect the global flow in the circulatory shock. Moreover, recent clinical studies found the P(v-a)CO₂ was related to the sublingual microcirculation perfusion in the sepsis. However, it is still controversial that whether P(v-a)CO₂ could be used to assess the microcirculatory flow in septic patients. Moreover, the related influent factors should be taken into account when interpreting P(v-a)CO₂ in clinical practice. This paper reviews the relevant experimental and clinical scenarios of P(v-a)CO₂ with the aim to help intensivists to use this parameter in the resuscitation of septic shock patients. Furthermore, we propose a conceptual framework to manage a high P(v-a)CO₂ value in the resuscitation of septic shock. The triggers of correcting an elevated P(v-a)CO₂ should take into consideration the other tissue perfusion parameters. Additionally, more evidence is required to validate that a decreasing in P(v-a)CO₂ by increasing cardiac output would result in improvement of microcirculation. Further investigations are necessary to clarify the relationship between P(v-a)CO₂ and microcirculation.

The validity of central venous to arterial carbon dioxide difference to predict adequate fluid management during living donor liver transplantation. A prospective observational study

BACKGROUND

To assess the validity of central and pulmonary veno-arterial CO₂ gradients to predict fluid responsiveness and to guide fluid management during liver transplantation.

METHODS

In adult recipients (ASA III to IV) scheduled for liver transplantation, intraoperative fluid management was guided by pulse pressure variations (PPV). PPV of ≥15% (Fluid Responding Status-FRS) indicated fluid resuscitation with 250 ml albumin 5% boluses repeated as required to restore PPV to < 15% (Fluid non-Responding Status-FnRS). Simultaneous blood samples from central venous and pulmonary artery catheters (PAC) were sent to calculate central venous to arterial CO₂ gap [C(v-a) CO2 gap] and pulmonary venous to arterial CO₂ gap [Pulm(p-a) CO2 gap]. CO and lactate were also measured.

RESULTS

Sixty seven data points were recorded (20 FRS and 47 FnRS). The discriminative ability of central and pulmonary CO₂ gaps between the two states (FRS and FnRS) was poor with AUC of ROC of 0.698 and 0.570 respectively. Central CO₂ gap was significantly higher in FRS than FnRS (P = 0.016), with no difference in the pulmonary CO₂ gap between both states. The central and Pulmonary CO₂ gaps are weakly correlated to PPV [r = 0.291, (P = 0.017) and r = 0.367, (P = 0.002) respectively]. There was no correlation between both CO₂ gaps and both CO and lactate.

CONCLUSION

Central and the Pulmonary CO₂ gaps cannot be used as valid tools to predict fluid responsiveness or to guide fluid management during liver transplantation. CO₂ gaps also do not correlate well with the changes in PPV or CO.

TRIAL REGISTRATION

Clinicaltrials.gov Identifier: NCT03123172 . Registered on 31-march-2017.

Relationship Analysis of Central Venous-to-arterial Carbon Dioxide Difference and Cardiac Index for Septic Shock

To analyze the relationship of the central venous-to-arterial carbon dioxide difference (p(cv-a)CO₂) and cardiac index (CI) in patients with septic shock, an observational study was conducted in intensive care unit (ICU). 66 consecutive patients with septic shock and central venous oxygen saturation (ScvO₂) ≥ 70% were included after early fluid resuscitation. Measurements were taken at a 6 h interval (T0, T6, T12, T18, T24) during first 24 h after their admission into ICU, including heart rate (HR), mean arterial pressure (MAP), central venous pressure (CVP), p(cv-a)CO₂, cardiac index(CI, L/(min•m²)) and ScvO₂. Patients were divided into low p(cv-a)CO₂ group (n = 35) and high p(cv-a)CO₂ group (n = 31) according to a threshold of 6 mmHg for p(cv-a)CO₂ at T0. As a result, at T0, T6, T12, T18 and T24, there were respectively significant differences between low and high p(cv-a)CO₂ groups for CI (4.1 ± 1.4 vs 2.4 ± 0.6, 4.4 ± 0.9 vs 2.8 ± 0.7, 4.1 ± 1.3 vs 2.9 ± 0.6, 4.0 ± 1.3 vs 2.7 ± 0.8, 4.2 ± 1.4 vs 2.9 ± 0.8, p < 0.001 at each time point), 28-day mortality rate was 38.7%(12/31) for high p(cv-a)CO₂ group and 22.8% (8/35) for low p(cv-a)CO₂ group (p > 0.05), there were significant differences for p(cv-a)CO₂ (p < 0.05) between low and high p(cv-a)CO₂ groups, no differences for HR, MAP, CVP, ScvO₂ (p > 0.05). CI was inversely correlated with p(cv-a)CO₂ value (r = −0.804, p < 0.001), but not for ScvO₂(r = 0.08, p > 0.05). Receiver operating characteristic curve analysis confirmed the correlation of p(cv-a)CO₂ with CI (AUC: 0.782;p < 0.001; 95% confidence interval: 0.710–0.853). The cut-off value for the best predictive value of CI ≥ 2.2 L/(min·m²) was p(cv-a)CO₂ of 5.55 mmHg or lower with a sensitivity of 85.7% and specificity of 66.8%. Hence CI measured with USCOM is inversely correlated with p(cv-a)CO₂ values in guiding the resuscitation of patients with septic shock.

Increased admission central venous-arterial CO2 difference predicts ICU-mortality in adult cardiac surgery patients

BACKGROUND

Invasive procedures such as cardiac surgery are associated with perioperative dysfunction of macrocirculation and/or microcirculation and organ failures. Maintenance or resuscitation of an adequate macrocirculation and/or microcirculation is thus crucial in patients after cardiac surgery. We investigated the prognostic power of early central venous-arterial carbon dioxide pressure difference (delta-pCO2) after cardiac surgery.

METHODS

Retrospective analysis of data from 1,019 cardiac surgery patients treated in the ICU of a tertiary medical care academic center. Clinical outcomes and laboratory measures including metabolic indices and calculated delta-pCO₂ were assessed. Receiver operating characteristic (ROC) curves were generated and sensitivity / specificity analysis was performed. Univariate and multivariate regression models were analyzed.

RESULTS

The area under the ROC curve for delta-pCO₂ to predict ICU mortality was 0.72 (sensitivity 65% / specificity 76%) with an optimal delta-pCO₂ cut-off value of 8.6 mmHg. In multivariate regression, delta-pCO₂ was associated with increased ICU mortality (HR 3.72, 95%-CI 1.3-10.66, p = 0.02). After adjustment for typical confounders, delta-pCO₂ remained as independent predictor of ICU mortality after cardiac surgery.

CONCLUSIONS

In a retrospective data analysis in a large sample of adult post cardiac surgery patients treated in the ICU, we observed that admission central venous-arterial delta-pCO₂ independently predicts ICU mortality. Delta-pCO₂ might thus contribute risk stratification in ICU patients after cardiac surgery.

Changes in tissue oxygen tension, venous saturation, and Fick-based assessments of cardiac output during hyperoxia

BACKGROUND

Hyperoxemia (arterial oxygen tension >100 mm Hg) may occur in critically ill patients and have effects on mixed venous saturation (SvO₂ ) and on Fick-based estimates of cardiac output (CO). We investigated the effect of hyperoxemia on SvO₂ and on assessments of CO using the Fick equation.

METHODS

Yorkshire swine (n = 14) were anesthetized, intubated, and paralyzed for instrumentation. SvO₂ (co-oximetry) and tissue oxygen tension (tPO₂ , implantable electrodes) in brain and myocardium were measured during systematic manipulation of arterial oxygen tension (PaO₂ ) using graded hyperoxia (fraction of inspired oxygen 0.21 → 0.8). Secondarily, oxygen- and carbon dioxide-based estimates of CO (Fick_O2 and Fick_{CO 2} , respectively) were compared with measurements from a flow probe placed on the aortic root.

RESULTS

Independent of changes in measured oxygen delivery, cerebral and myocardial tPO₂ increased in proportion to PaO₂ , as did SvO₂ (P < 0.001 for all). Based on mixed model analysis, each 100 mm Hg increase in PaO₂ resulted in a 4.8 ± 0.9% increase in SvO₂ under the conditions tested. Because neither measured oxygen consumption, arterial oxyhemoglobin saturation or cardiac output varied significantly during hyperoxia, changes in SvO₂ resulted in successively increasing errors in Fick_O2 during hyperoxia (34% during normoxia, 72% during FiO₂ 0.8). Fick_{CO 2} lacked the progressively worsening errors present in Fick_O2 , but correlated poorly with CO.

CONCLUSION

SvO₂ acutely changes following changes in PaO₂ even absent changes in measured DO₂ . This may lead to errors in Fick_O2 estimates of CI. Further work is necessary to understand the impact of this phenomenon in disease states.

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.

Risk indicators for acute kidney injury in cardiogenic shock

PURPOSE

In critical illness, the relation between the macrocirculation, microcirculation and organ dysfunction, such as acute kidney injury (AKI), is complex. This study aimed at identifying predictors for AKI in patients with cardiogenic shock.

MATERIALS AND METHODS

Thirty-nine adult cardiogenic shock patients, with an admission creatinine <200 μmol l^-1, and whose microcirculation was measured within 48 h were enrolled. Patient data were analyzed if AKI stage ≥1 developed according to the Kidney Disease/Improving Outcomes classification within 48 h after admission. Variables with a p < .05 in the univariate analysis were considered for analysis with logistic regression.

RESULTS

Twenty-four patients (61.5%) developed AKI within 48 h. The group that developed AKI had higher central venous pressures (CVP), lower diastolic arterial blood pressures and mean perfusion pressures, higher maximum ventilator pressures as well as positive end expiratory pressures and were treated with higher dosages of dobutamine. There was no difference of the microcirculation. In the multivariate logistic regression analysis, CVP was the only independent predictor for AKI (OR 1.241; 95% CI 1.030-1.495; p = .023).

CONCLUSIONS

In this population of patients with cardiogenic shock, CVP was associated with the development of AKI.

Mean arterial pressure targeted fluid resuscitation may lead to fluid overload: A bleeding-resuscitation animal experiment

Introduction

Fluid resuscitation is the cornerstone of treatment in hemorrhagic shock. Despite increasing doubts, several guidelines recommend to maintain mean arterial pressure (MAP) >65 mmHg as the most frequent indication of fluid therapy. Our aim was to investigate the effects of a MAP-guided management in a bleeding-resuscitation animal experiment.

Materials and methods

After anesthesia and instrumentation (t_bsl) animals were bled till the initial stroke volume index dropped by 50% (t₀). Fluid replacement was performed in 4 equivalent steps (t_1-4) with balanced crystalloid solution to reach the baseline values of MAP. Invasive hemodynamic measurements and blood gas analyses were performed after each step.

Results

Mean arterial pressure dropped from t_bsl to t₀ (114±11 vs 76.9±16.9 mmHg, p<0.001) and returned to baseline by t₄ (101.4±14.4 mmHg). From t_bsl-t₀ stroke volume index (SVI), cardiac index (CI) decreased (SVI: 40±8.6 vs 19.3±3.6 ml/m², p<0.001; CI: 3.4±0.3 vs 1.9±0.3 l/min/m², p<0.001), pulse pressure variation (PPV) increased (13.2±4.3 vs 22.1±4.3%, p<0.001). There was a decrease in oxygen delivery (464±45 vs 246±26.9 ml/min, p<0.001), central venous oxygen saturation (82.8±5.4 vs 53.6±12.1%, p<0.001) and increase in lactate levels (1.6±0.4 vs 3.5±1.6 mmol/l, p<0.005). SVI, CI and PPV returned to their initial values by t₂. To normalize MAP fluid therapy had to be continued till t₄, with the total infused volume of 4.5±0.8 l.

Conclusion

In the current experiment bleeding led to hemorrhagic shock, while MAP remained higher than 65 mmHg. Furthermore, MAP was unable to indicate the normalization of SVI, CI and PPV that resulted in unnecessary fluid administration. Our data give further evidence that MAP may be an inappropriate parameter to follow during fluid resuscitation.

Protocolized care for early shock resuscitation

PURPOSE OF REVIEW

Protocolized care for early shock resuscitation (PCESR) has been intensely examined over the last decade. The purpose is to review the pathophysiologic basis, historical origin, clinical applications, components and outcome implications of PCESR.

RECENT FINDINGS

PCESR is a multifaceted systems-based approach that includes early detection of high-risk patients and interventions to rapidly reverse hemodynamic perturbations that result in global or regional tissue hypoxia. It has been applied to perioperative surgery, trauma, cardiology (heart failure and acute myocardial infarction), pulmonary embolus, cardiac arrest, undifferentiated shock, postoperative cardiac surgery and pediatric septic shock. When this approach is used for adult septic shock, in particular, it is associated with a mortality reduction from 46.5 to less than 30% over the last 2 decades. Challenges to these findings are seen when repeated trials contain enrollment, diagnostic and therapeutic methodological differences.

SUMMARY

PCESR is more than a hemodynamic optimization procedure. It also provides an educational framework for the less experienced and objective recognition of clinical improvement or deterioration. It further minimizes practices' variation and provides objective measures that can be audited, evaluated and amendable to continuous quality improvement. As a result, morbidity and mortality are improved.

Estimating Arterial Partial Pressure of Carbon Dioxide in Ventilated Patients: How Valid Are Surrogate Measures?

The arterial partial pressure of carbon dioxide (Pa_CO2) is an important parameter in critically ill, mechanically ventilated patients. To limit invasive procedures or for more continuous monitoring of Pa_CO2, clinicians often rely on venous blood gases, capnography, or transcutaneous monitoring. Each of these has advantages and limitations. Central venous Pco₂ allows accurate estimation of Pa_CO2, differing from it by an amount described by the Fick principle. As long as cardiac output is relatively normal, central venous Pco₂ exceeds the arterial value by approximately 4 mm Hg. In contrast, peripheral venous Pco₂ is a poor predictor of Pa_CO2, and we do not recommend using peripheral venous Pco₂ in this manner. Capnography offers measurement of the end-tidal Pco₂ (Pet_CO2), a value that is close to Pa_CO2 when the lung is healthy. It has the advantage of being noninvasive and continuously available. In mechanically ventilated patients with lung disease, however, Pet_CO2 often differs from Pa_CO2, sometimes by a large degree, often seriously underestimating the arterial value. Dependence of Pet_CO2 on alveolar dead space and ventilator expiratory time limits its value to predict Pa_CO2. When lung function or ventilator settings change, Pet_CO2 and Pa_CO2 can vary in different directions, producing further uncertainty. Transcutaneous Pco₂ measurement has become practical and reliable. It is promising for judging steady state values for Pa_CO2 unless there is overt vasoconstriction of the skin. Moreover, it can be useful in conditions where capnography fails (high-frequency ventilation) or where arterial blood gas analysis is burdensome (clinic or home management of mechanical ventilation).

Assessing Acid–Base Status in Circulatory Failure: Relationship Between Arterial and Peripheral Venous Blood Gas Measurements in Hypovolemic Shock

Background and Objectives:

In severe circulatory failure agreement between arterial and mixed venous or central venous values is poor; venous values are more reflective of tissue acid–base imbalance. No prior study has examined the relationship between peripheral venous blood gas (VBG) values and arterial blood gas (ABG) values in hemodynamic compromise. The objective of this study was to examine the correlation between hemodynamic parameters, specifically systolic blood pressure (SBP) and the arterial–peripheral venous (A-PV) difference for all commonly used acid–base parameters (pH, Pco 2, and bicarbonate).

Design, Setting, Participants, and Measurements:

Data were obtained prospectively from adult patients with trauma. When an ABG was obtained for clinical purposes, a VBG was drawn as soon as possible. Patients were excluded if the ABG and VBG were drawn >10 minutes apart.

Results:

The correlations between A-PV pH, A-PV Pco 2, and A-PV bicarbonate and SBP were not statistically significant ( P = .55, .17, and .09, respectively). Although patients with hypotension had a lower mean arterial and peripheral venous pH and bicarbonate compared to hemodynamically stable patients, mean A-PV differences for pH and Pco 2 were not statistically different ( P = .24 and .16, respectively) between hypotensive and normotensive groups.

Conclusions:

In hypovolemic shock, the peripheral VBG does not demonstrate a higher CO2 concentration and lower pH compared to arterial blood. Therefore, the peripheral VBG is not a surrogate for the tissue acid–base status in hypovolemic shock, likely due to peripheral vasoconstriction and central shunting of blood to essential organs. This contrasts with the selective venous respiratory acidosis previously demonstrated in central venous and mixed venous measurements in circulatory failure, which is more reflective of acid–base imbalance at the tissue level than arterial blood. Further work needs to be done to better define the relationship between ABG and both central and peripheral VBG values in various types of shock.

Monitoring of Tissue Oxygenation: an Everyday Clinical Challenge

Purpose of review

The aim of this article is to study the overview of pathophysiology and clinical application of central venous oxygen saturation monitoring in critically ill patients and during the perioperative period.

Recent findings

There are several clinical studies and animal experiments evaluating the effects of goal-directed hemodynamic stabilization on critically ill patients. Recent systematic reviews and meta-analyses found that advanced hemodynamic endpoints-targeted management has a positive effect on outcome in high-risk surgical patients. As all interventions aim to improve tissue oxygenation, it is of utmost importance to monitor the balance between oxygen delivery and consumption. For this purpose, central venous blood gas analysis provides an easily available tool in the everyday clinical practice. The adequate interpretation of central venous oxygen saturation renders the need of careful evaluation of several physiological and pathophysiological circumstances. When appropriately evaluated, central venous oxygen saturation can be a valuable component of a multimodal individualized approach, in which components of oxygen delivery are put in the context of the patients' individual oxygen consumption. In addition to guide therapy, central venous oxygen saturation may also serve as an early warning sign of inadequate oxygen delivery, which would otherwise remain hidden from the attending physician.

Summary

With the incorporation of central venous oxygen saturation in the everyday clinical routine, treatment could be better tailored for the patients' actual needs; hence, it may also improve outcome.