Central venous-to-arterial carbon dioxide difference and the effect of venous hyperoxia: A limiting factor, or an additional marker of severity in shock?

MORTALITY OF SEPTIC SHOCK SECONDARY TO PEDIATRIC PRIMARY PERITONITIS PREDICTED BY RESPIRATORY QUOTIENT COMBINED WITH LACTATE: A SURVEY FROM TWO CHILDREN'S HOSPITALS IN NORTHWEST CHINA

ABSTRACT

Background: Pediatric sepsis is a life-threatening condition, with extremely high incidence and mortality among critically ill children worldwide. Patients with septic shock are susceptible to intestinal complications due to altered blood flow distribution, and these complications often correlate directly with a poor prognosis. Early detection of low perfusion and appropriate resuscitation are critical components in the management of patients experiencing shock. Nevertheless, significant debate persists regarding the comparative value of various resuscitation targets. While central venous oxygen saturation (ScvO2) monitoring is frequently advocated, it remains a subject of scrutiny. All pathophysiological mechanisms are intricately linked to cellular hypoxia and energy metabolism, which is why metabolic-related biomarkers, particularly lactate and lactate clearance rate, are highly regarded by critical care experts. Nonetheless, limited research has been conducted on the association between markers of circulatory shock and metabolic disorders in critically ill patients particularly in the field of pediatrics. Physiological indicators, particularly those associated with cell energy metabolism, have shown potentials in predicting sepsis and septic shock. Methods: This was a retrospective study. A total of 63 patients, comprising 30 males and 33 females, who developed septic shock secondary to pediatric primary peritonitis, were admitted to the Intensive Care Department of the Children's Hospital Affiliated to Xi'an Jiaotong University and the Pediatric Intensive Care Unit of Gansu Provincial Maternity and Child-Care Hospital between December 2016 and December 2021. Based on the primary outcome of 28-day all-cause mortality, patients were assigned into the survival group and nonsurvival group. Demographic and clinical data were compared. Risk factors for the prognosis of septic shock secondary to pediatric primary peritonitis were identified by logistic regression, and their potentials in predicting the 28-day survival were assessed by the receiver operating characteristic and Kaplan-Meier survival curves. Results: Among the 63 eligible patients with septic shock secondary to pediatric primary peritonitis, 47 survived. In comparison to the survival group, the nonsurvival group showed significantly higher proportions of mechanical ventilation, surgical intervention, and use of vasoactive drugs, procalcitonin, activated partial thromboplastin time, respiratory quotient (RQ), lactate (Lac), the Pediatric Sequential Organ Failure Assessment score, and the Pediatric Risk of Mortality III score, but lower platelet count, fibrinogen, and mean arterial pressure (all P's < 0.05). RQ (odds ratio [OR], 2.37; 95% confidence interval [CI], 1.41, 3.22; P < 0.05) and Lac (OR, 2.01; 95% CI, 1.15, 3.21; P < 0.05) were independent prognostic factors for septic shock secondary to pediatric primary peritonitis. Their combination (RQ < 1.6 + Lac < 4 mmol/L) achieved a better accuracy in predicting the 28-day cumulative survival. Conclusion: RQ combined with Lac offers an excellent performance in predicting mortality of septic shock secondary to pediatric primary peritonitis.

Evaluating tissue hypoxia and the response to fluid administration in septic shock patients: a metabolic cluster analysis

BACKGROUND

The selection of adequate indicators of tissue hypoxia for guiding the resuscitation process of septic patients is a highly relevant issue. Current guidelines advocate for the use of lactate as sole metabolic marker, which may be markedly limited, and the integration of different variables seems more adequate. In this study, we explored the metabolic profile and its implications in the response to the administration of a fluid challenge in early septic shock patients.

METHODS

Observational study including septic shock patients within 24 h of ICU admission, monitored with a cardiac output estimation system, with ongoing resuscitation. Hemodynamic and metabolic variables were measured before and after a fluid challenge (FC). A two-step cluster analysis was used to define the baseline metabolic profile, including lactate, central venous oxygen saturation (ScvO2), central venous-to-arterial carbon dioxide difference (PcvaCO2), and PcvaCO2 corrected by the difference in arterial-to-venous oxygen content (PcvaCO2/CavO2).

RESULTS

Seventy-seven fluid challenges were analyzed. Cluster analysis revealed two distinct metabolic profiles at baseline. Cluster A exhibited lower ScvO2, higher PcvaCO2, and lower PcvaCO2/CavO2. Increases in cardiac output (CO) were associated with increases in VO2 exclusively in cluster A. Baseline isolated metabolic variables did not correlate with VO2 response, and changes in ScvO2 and PcvaCO2 were associated to VO2 increase only in cluster A.

CONCLUSIONS

In a population of early septic shock patients, two distinct metabolic profiles were identified, suggesting tissue hypoxia or dysoxia. Integrating metabolic variables enhances the ability to detect those patients whose VO2 might increase as results of fluid administration.

Can perioperative pCO2 gaps predict complications in patients undergoing major elective abdominal surgery randomized to goal-directed therapy or standard care? A secondary analysis

The difference between venous and arterial carbon dioxide pressure (pCO2 gap), has been used as a diagnostic and prognostic tool. We aimed to assess whether perioperative pCO2 gaps can predict postoperative complications. This was a secondary analysis of a multicenter RCT comparing goal-directed therapy (GDT) to standard care in which 464 patients undergoing high-risk elective abdominal surgery were included. Arterial and central venous blood samples were simultaneously obtained at four time points: after induction, at the end of surgery, at PACU/ICU admission, and PACU/ICU discharge. Complications within the first 30 days after surgery were recorded. Similar pCO2 gaps were found in patients with and without complications, except for the pCO2 gap at the end of surgery, which was higher in patients with complications (6.0 mmHg [5.0-8.0] vs. 6.0 mmHg [4.1-7.5], p = 0.005). The area under receiver operating characteristics curves for predicting complications from pCO2 gaps at all time points were between 0.5 and 0.6. A weak correlation between ScvO2 and pCO2 gaps was found for all timepoints (ρ was between - 0.40 and - 0.29 for all timepoints, p < 0.001). The pCO2 gap did not differ between GDT and standard care at any of the selected time points. In our study, pCO2 gap was a poor predictor of major postoperative complications at all selected time points. Our research does not support the use of pCO2 gap as a prognostic tool after high-risk abdominal surgery. pCO2 gaps were comparable between GDT and standard care. Clinical trial registration Netherlands Trial Registry NTR3380.

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.

Comparison of central venous minus arterial carbon dioxide pressure to arterial minus central venous oxygen content ratio and lactate levels as predictors of mortality in critically ill patients: a systematic review and meta-analysis

OBJECTIVE

The central venousarterial carbon dioxide pressure to arterial-central venous oxygen content ratio (Pcv-aCO2/Ca-cvO2) is frequently used as a surrogate for tissue oxygenation. We aimed to identify and synthesize literature and quality of evidence supporting Pcv-aCO2/Ca-cvO2 as a predictor of mortality in critically ill patients compared with lactate.

METHODS

We searched several databases for studies measuring Pcv-aCO2/Ca-cvO2 in critically ill patients. Independent investigators performed the article screening and data extraction. A random-effects metaanalysis was performed. Pooled standardized mean differences (SMD) were used to compare the prognostic ability of Pcv-aCO2/Ca-cvO2 and lactate.

RESULTS

We initially retrieved 172 studies; 17 were included for qualitative description, and 10 were included for quantitative synthesis. The mean Pcv-aCO2/Ca-cvO2 was higher in nonsurvivors than in survivors (pooled SMD = 0.75; 95%CI 0.34 - 1.17; I2 = 83%), as was the case with lactate levels (pooled SMD = 0.94; 95%CI 0.34 - 1.54; I2 = 92%). Both tests were statistically significant predictors of mortality, albeit with overlapping 95%CIs between them.

CONCLUSION

Moderate-quality evidence showed little or no difference in the ability of Pcv-aCO2/Ca-cvO2, compared with lactate, to predict mortality. Nevertheless, our conclusions are limited by the considerable heterogeneity among the studies.PROSPERO registration: CRD42019130387.

Correlation of central venous-to-arterial carbon dioxide difference to arterial-central venous oxygen difference ratio to lactate clearance and prognosis in patients with septic shock: A prospective observational cohort study

Background

To assess the relationship between the ratio of difference of venoarterial CO₂ tension (P (v-a) CO₂) and difference of arterio-venous oxygen content (C (a-cv) O₂), i.e., ΔPCO₂/ΔCaO₂ with lactate clearance (LC) at 8 and 24 h, to define a cutoff for the ratio to identify LC >10% and >20% at 8 and 24 h, respectively, and its association with prognosis in septic shock.

Methods

Adult patients with septic shock were included in this prospective, observational cohort study. Blood samples for arterial lactate, arterial, and central venous oxygen and carbon dioxide were drawn simultaneously at time zero (T0), 8 h (T8), and 24 h (T24). At T8, patients were divided into Group 8A (LC ≥10%) and Group 8B (LC <10%). At T24, patients were divided into Group 24A (LC ≥20%) and Group 24B (LC <20%).

Results

Ninty-eight patients were included. The area under the curve of ΔPCO₂/ΔCaO₂ at T8 (0.596) and T24 (0.823) was the highest when compared to P(v-a) CO₂ and C(a-v) O₂. The best cutoff of P(v-a) CO₂/C (a-v) O₂ as predictor of LC >10% was 1.31 (sensitivity 70.6% and specificity 53.3%) and for LC >20% was 1.37 (sensitivity 100% and specificity 50%). At both T8 and T24, P(v-a) CO₂/C (a-v) O₂ showed a significant negative correlation with LC. Groups 8A and 24A showed lower intensive care unit mortality than 8B and 24B, respectively. Values of P(v-a) CO₂/C (a-v) O₂ at T8 were comparable, but at T24, there was a significant difference between the survivors and nonsurvivors (P < 0.001).

Conclusion

ΔPCO₂/ΔCaO₂ predicts lactate clearance, and its 24 h value appears superior to the 8-h value in predicting LC and mortality in septic shock patients.

Changes in central venous-to-arterial carbon dioxide tension induced by fluid bolus in critically ill patients

BACKGROUND

In this prospective observational study, we evaluated the effects of fluid bolus (FB) on venous-to-arterial carbon dioxide tension (PvaCO2) in 42 adult critically ill patients with pre-infusion PvaCO2 > 6 mmHg.

RESULTS

FB caused a decrease in PvaCO2, from 8.7 [7.6-10.9] mmHg to 6.9 [5.8-8.6] mmHg (p < 0.01). PvaCO2 decreased independently of pre-infusion cardiac index and PvaCO2 changes during FB were not correlated with changes in central venous oxygen saturation (ScvO2) whatever pre-infusion CI. Pre-infusion levels of PvaCO2 were inversely correlated with decreases in PvaCO2 during FB and a pre-infusion PvaCO2 value < 7.7 mmHg could exclude a decrease in PvaCO2 during FB (AUC: 0.79, 95%CI 0.64-0.93; Sensitivity, 91%; Specificity, 55%; p < 0.01).

CONCLUSIONS

Fluid bolus decreased abnormal PvaCO2 levels independently of pre-infusion CI. Low baseline PvaCO2 values suggest that a positive response to FB is unlikely.

Pathophysiology and clinical implications of the veno-arterial PCO2 gap

This article is one of ten reviews selected from the Annual Update in Intensive Care and Emergency Medicine 2021. Other selected articles can be found online at https://www.biomedcentral.com/collections/annualupdate2021 . Further information about the Annual Update in Intensive Care and Emergency Medicine is available from https://link.springer.com/bookseries/8901 .

Changes in central venous to arterial carbon dioxide gap (PCO2 gap) in response to acute changes in ventilation

Background

Early diagnosis of shock is a predetermining factor for a good prognosis in intensive care. An elevated central venous to arterial PCO₂ difference (∆PCO₂) over 0.8 kPa (6 mm Hg) is indicative of low blood flow states. Disturbances around the time of blood sampling could result in inaccurate calculations of ∆PCO₂, thereby misrepresenting the patient status. This study aimed to determine the influences of acute changes in ventilation on ∆PCO₂ and understand its clinical implications.

Methods

To investigate the isolated effects of changes in ventilation on ∆PCO₂, eight pigs were studied in a prospective observational cohort. Arterial and central venous catheters were inserted following anaesthetisation. Baseline ventilator settings were titrated to achieve an EtCO₂ of 5±0.5 kPa (V_T = 8 mL/kg, Freq = 14 ± 2/min). Blood was sampled simultaneously from both catheters at baseline and 30, 60, 90, 120, 180 and 240 s after a change in ventilation. Pigs were subjected to both hyperventilation and hypoventilation, wherein the respiratory frequency was doubled or halved from baseline. ∆PCO₂ changes from baseline were analysed using repeated measures ANOVA with post-hoc analysis using Bonferroni’s correction.

Results

∆PCO₂ at baseline for all pigs was 0.76±0.29 kPa (5.7±2.2 mm Hg). Following hyperventilation, there was a rapid increase in the ∆PCO₂, increasing maximally to 1.35±0.29 kPa (10.1±2.2 mm Hg). A corresponding decrease in the ∆PCO₂ was seen following hypoventilation, decreasing maximally to 0.23±0.31 kPa (1.7±2.3 mm Hg). These changes were statistically significant from baseline 30 s after the change in ventilation.

Conclusion

Disturbances around the time of blood sampling can rapidly affect the PCO₂, leading to inaccurate calculations of the ∆PCO₂, resulting in misinterpretation of patient status. Care should be taken when interpreting blood gases, if there is doubt as to the presence of acute and transient changes in ventilation.

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).

Veno-arterial CO2 difference and respiratory quotient after cardiac arrest: An observational cohort study

PURPOSE

To characterize venous-arterial CO₂ difference (ΔpCO₂) and the respiratory quotient (RQ) in post cardiac arrest patients and evaluate the association between these parameters and patient outcome.

MATERIALS AND METHODS

Data were obtained retrospectively from post cardiac arrest patients admitted between 2007 and 2016 to a medical intensive care unit. Comatose, adult patients in whom arterial and venous blood gas analyses were concomitantly performed in the first 24 h were included. Patients were grouped according to the time-point of sampling; 0-6, 6-12 and 12-24 h after admission.

RESULTS

308 patients were included; 174 (56%) died before ICU discharge and 212 (69%) had an unfavorable neurologic outcome. RQ was associated with ICU mortality (OR:1.09 (95%CI: 1.04-1.14; p < 0.01)), although not with neurological outcome. ΔpCO₂ was negatively associated with both ICU mortality (OR: 0.92 (95%CI: 0.86-0.99; p = 0.02)) and poor neurologic outcome (adjusted OR: 0.93 (95%CI: 0.87-0.99; p = 0.02)). ΔpCO₂ predicted an elevated RQ; a ΔpCO₂ above 8.5 mmHg identified a high RQ with reasonable sensitivity and specificity.

CONCLUSIONS

RQ was associated with ICU mortality and ΔpCO₂ identified elevated RQ in the early phase after cardiac arrest. However, ΔpCO₂ were negatively associated with both ICU mortality and neurologic outcome.

Hemodynamic monitoring with two blood gases: “a tool that does not go out of style”

Introduction. Hemodynamic monitoring of a critically ill patient is an indispensable tool both inside and outside intensive care; we currently have invasive, minimally invasive and non-invasive devices; however, no device has been shown to have a positive impact on the patient's evolution; arterial and venous blood gases provide information on the patient's actual microcirculatory and metabolic status and may be a hemodynamic monitoring tool. Objective. To carry out a non-systematic review of the literature of hemodynamic monitoring carried out through the variables obtained in arterial and venous blood gases. Material and methods. A non-systematic review of the literature was performed in the PubMed, OvidSP and ScienceDirect databases with selection of articles from 2000 to 2019. Results. It was found that there are variables obtained in arterial and venous blood gases such as central venous oxygen saturation (SvcO2), venous-to-arterial carbon dioxide pressure (∆pv-aCO2), venous-to-arterial carbon dioxide pressure/arteriovenous oxygen content difference (∆pv-aCO2/∆Ca-vO2) that are related to cellular oxygenation, cardiac output (CO), microcirculatory veno-arterial flow and anaerobic metabolism and allow to assess tissue perfusion status. Conclusion. The variables obtained by arterial and venous blood gases allow for non-invasive, accessible and affordable hemodynamic monitoring that can guide medical decision-making in critically ill patients.

How can CO2-derived indices guide resuscitation in critically ill patients?

Assessing the adequacy of oxygen delivery with oxygen requirements is one of the key-goal of haemodynamic resuscitation. Clinical examination, lactate and central or mixed venous oxygen saturation (S_vO₂ and S_cvO₂, respectively) all have their limitations. Many of them may be overcome by the use of the carbon dioxide (CO₂)-derived variables. The venoarterial difference in CO₂ tension ("ΔPCO₂" or "PCO₂ gap") is not an indicator of anaerobic metabolism since it is influenced by the oxygen consumption. By contrast, it reliably indicates whether blood flow is sufficient to carry CO₂ from the peripheral tissue to the lungs in view of its clearance: it, thus, reflects the adequacy of cardiac output with the metabolic condition. The ratio of the PCO₂ gap with the arteriovenous difference of oxygen content (PCO₂ gap/C_a-vO₂) might be a marker of anaerobiosis. Conversely to S_vO₂ and S_cvO₂, it remains interpretable if the oxygen extraction is impaired as it is in case of sepsis. Compared to lactate, it has the main advantage to change without delay and to provide a real-time monitoring of tissue hypoxia.

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.

Central venous-to-arterial carbon dioxide difference combined with arterial-to-venous oxygen content difference (PcvaCO2/CavO2) reflects microcirculatory oxygenation alterations in early septic shock

PURPOSE

To explore the relationship between central venous-to-arterial carbon dioxide difference (P_cvaCO₂), P_cvaCO₂/arterial-venous oxygen content difference ratio (P_cvaCO₂/C_avO₂) and the microcirculatory status, evaluated by using near-infrared spectroscopy, in septic shock patients.

METHODS

Observational study in a 30-bed mixed ICU. Fifty septic shock patients within the first 24 h of ICU admission were studied. After restoration of mean arterial pressure, hemodynamic, metabolic and microcirculatory parameters were simultaneously evaluated. Local tissue oxygen saturation (StO₂), and local hemoglobin index (THI) were measured on the thenar eminence by means of near-infrared spectroscopy. A transient vascular occlusion test was performed in order to obtain StO₂ deoxygenation rate (DeO₂), local oxygen consumption (nirVO₂), and reoxgenation rate (ReO₂).

RESULTS

At inclusion, increased P_cvaCO₂ values were associated with lower StO₂ and THI, whereas increased P_cvaCO₂/C_avO₂ values were associated with lower DeO₂, nirVO₂, and ReO₂. Multiple regression models confirmed the association between P_cvaCO₂/C_avO₂ and nirVO₂, while P_cvaCO₂ was only related to CI, and not to microcirculatory parameters.

CONCLUSIONS

In a population of early septic shock patients, increases in P_cvaCO₂ and P_cvaCO₂/C_avO₂ reflected different alterations at the microcirculatory level. While P_cvaCO₂ was related to global flow, the P_cvaCO₂/C_avO₂ ratio was associated to impaired local oxygen utilization and diminished microvascular reactivity.

Pcv-aCO2/Ca-cvO2 Combined With Arterial Lactate Clearance Rate as Early Resuscitation Goals in Septic Shock

BACKGROUND

We aimed to investigate the prognostic significance of central venous-arterial carbon dioxide tension to arterial-central venous oxygen content ratio (Pcv-aCO₂/Ca-cvO₂) combined with arterial lactate clearance rate (LCR) as early resuscitation goals in septic shock.

MATERIALS AND METHODS

We enrolled 145 septic shock patients admitted to our department from March 2013 to May 2017 in this study. They all received an initial resuscitation therapy according to the Surviving Sepsis Campaign guideline, and were classified into 4 groups according to Pcv-aCO₂/Ca-cvO₂ and LCR at 6 hours after resuscitation (T6): Group A: Pcv-aCO₂/Ca-cvO₂ > 1.8, LCR < 30%; Group B: Pcv-aCO₂/Ca-cvO₂ > 1.8, LCR ≥ 30%; Group C: Pcv-aCO₂/Ca-cvO₂ ≤ 1.8, LCR < 30% and Group D: Pcv-aCO₂/Ca-cvO₂ ≤ 1.8, LCR ≥ 30%. General demographics, hemodynamic parameters, metabolic parameters, Acute Physiology and Chronic Health Evaluation II scores, Sequential Organ Failure Assessment scores, length of intensive care unit stay and 28-day mortality were compared among groups.

RESULTS

Group D had the lowest Acute Physiology and Chronic Health Evaluation II and Sequential Organ Failure Assessment score at day 3, the shortest intensive care unit stay and the lowest 28-day mortality. Kaplan-Meier survival curves up to day 28 showed group D had the longest median survival time. Pcv-aCO₂/Ca-cvO₂ and LCR at T6 were independent predictors of 28-day mortality. The area under ROC curve for Pcv-aCO₂/Ca-cvO₂ combined with LCR was significantly greater than either Pcv-aCO₂/Ca-cvO₂ or LCR alone (both P < 0.05).

CONCLUSIONS

Combination of Pcv-aCO₂/Ca-cvO₂ ratio and LCR is better than either alone to predict the adverse outcomes in septic shock, and may provide useful information for assessing the adequacy of resuscitation in early-stage septic shock.

Respiratory quotient estimations as additional prognostic tools in early septic shock

Central venous-to-arterial carbon dioxide difference (P_cvaCO₂), and its correction by the arterial-to-venous oxygen content difference (P_cvaCO₂/C_avO₂) have been proposed as additional tools to evaluate tissue hypoxia. Since the relationship between pressure and content of CO₂ (CCO₂) might be affected by several factors, some authors advocate for the use of C_cvaCO₂/C_avO₂. The aim of the present study was to explore the factors that might intervene in the difference between P_cvaCO₂/C_avO₂ and C_cvaCO₂/C_avO₂, and to analyze their association with mortality. Observational study in a 30-bed mixed ICU. Fifty-two septic shock patients within the first 24 h of ICU admission were studied. After restoration of mean arterial pressure, hemodynamic and metabolic parameters were evaluated. A total of 110 sets of measurements were performed. Simultaneous P_cvaCO₂/C_avO₂ and C_cvaCO₂/C_avO₂ values were correlated, but agreement analysis showed a significant proportional bias. The difference between P_cvaCO₂/C_avO₂ and C_cvaCO₂/C_avO₂ was independently associated with pH, S_cvO₂, baseline C_cvaCO₂/C_avO₂ and hemoglobin. A stepwise regression analysis showed that pH was the single best predictor for the magnitude of such difference, with very limited effect of other variables. At inclusion, variables associated with ICU-mortality were lactate, pH, P_cvaCO₂/C_avO₂, and the difference between P_cvaCO₂/C_avO₂ and C_cvaCO₂/C_avO₂. Initial S_cvO₂, P_cvaCO₂, C_cvaCO₂/C_avO₂, and cardiac index were not different in survivors and non-survivors. In a population of early septic shock patients, simultaneous values of P_cvaCO₂/C_avO₂ and C_cvaCO₂/C_avO₂ were not equivalent, and the main determinant of the magnitude of the difference between these two parameters was pH. The P_cvaCO₂/C_avO₂ ratio was associated with ICU mortality, whereas C_cvaCO₂/C_avO₂ was not.