Central venous-to-arterial CO2 difference as a biomarker of outcome in children who underwent surgery for congenital heart disease / Diferencia arteriovenosa de CO2 como biomarcador de desenlace en niños operados de cardiopatías congénitas

Abstract Background: In congenital heart surgery, low cardiac output syndrome (LCOS) is a major cause of morbidity in the immediate post-operative period. A decrease in cardiac output leads to an increase in tissue oxygen consumption. Several biomarkers such as venous oxygen saturation (SvO2), arteriovenous oxygen difference (DavO2), and lactate can assess tissue perfusion in the presence of LCOS. Recently, central venous to arterial CO2 difference (ΔCO2) has been proposed as a biomarker of tissue ischemia that could be used as a predictor of death in neonatal patients. This study aimed to analyze the relationship between ΔCO2 and immediate post-operative outcomes in pediatric patients undergoing congenital heart surgery and its correlation with DavO2, SvO2, and lactate. Methods: We conducted a longitudinal study of patients aged 0-18 years who underwent congenital heart surgery with or without cardiopulmonary bypass at the Instituto Nacional de Pediatría, from March 2019 to March 2021. Results: Eighty-two patients were included; the median age was 17 months. About 59% had a ΔCO2 ≥ 6 mmHg. Patients with ΔCO2 ≥ 6 mmHg had a vasoactive-inotropic score > 5 (p < 0.001), DavO2 > 5 mL/dL (p = 0.048), and lactate > 2 mmol/L (p = 0.027), as well as a longer hospital stay (p = 0.043). Patients with ΔCO2 > 6 mmHg and vasoactive-inotropic score ≥ 10 were 12.6 times more likely to die. Conclusion: ΔCO2 is a good marker of tissue hypoperfusion and outcome in the post-operative period of congenital heart surgery.

Resumen Introducción: En la cirugía cardiaca de malformaciones congénitas, el síndrome de bajo gasto cardiaco (SBGC) es una de las principales causas de morbilidad en el postoperatorio inmediato. La caída del gasto cardiaco aumenta el consumo de oxígeno en los tejidos. Varios biomarcadores, como la saturación venosa de oxígeno (SvO2), la diferencia arteriovenosa de oxígeno (DavO2) y el lactato han sido utilizados como indicadores hipoperfusión tisular en presencia de SBGC. Recientemente, la diferencia arteriovenosa de CO2 (ΔCO2) se ha propuesto como otro biomarcador de isquemia tisular que podría utilizarse como predictor de muerte en pacientes en edad neonatal. El objetivo de este estudio fue analizar la relación entre la ΔCO2 y la evolución postoperatoria de pacientes pediátricos operados de cardiopatías congénitas y correlacionarlo con la DavO2, SvO2 y lactato. Métodos: Se realizó un estudio longitudinal en pacientes de 0 a 18 años operados de corazón con empleo de bomba de circulación extracorpórea en el Instituto Nacional de Pediatría. Resultados: Se incluyeron 82 pacientes; la mediana de edad fue de 17 meses. El 59% presentó un ΔCO2 > 6 mmHg. Los pacientes con un ΔCO2 > 6 mmHg mostraron un puntaje de inotrópicos > 5 (p < 0.001), DavO2 > 5 mL/dL (p = 0.048) y lactato > 2 mmol/L (p = 0.027), así como mayor estancia hospitalaria (p = 0.043). Los pacientes con ΔCO2 > 6 mmHg y un puntaje de inotrópicos ≥ 10 presentaron una probabilidad de muerte 12.6 veces mayor. Conclusiones: El ΔCO2 en el periodo postoperatorio de una cirugía cardiaca congénita es un buen marcador de hipoperfusión tisular y de desenlace.

Acute hyperventilation increases oxygen consumption and decreases peripheral tissue perfusion in critically ill patients.

PURPOSE: This study aimed to evaluate the effects of acute hyperventilation on central venous-to-arterial carbon dioxide tension difference (Pv-aCO2), central venous oxygen saturation (ScvO2), central venous-to-arterial CO2 difference/arterial-central venous O2 difference ratio (CO2GAP-Ratio), and peripheral perfusion index (PI) in hemodynamically stable critically ill patients. METHODS: Fifty-four mechanically ventilated patients were evaluated. The cardiac index, Pv-aCO2, ScvO2, CO2GAP-Ratio, PI, and arterial and venous blood gas parameters were measured in the first set of measurements. Then, alveolar ventilation was increased by raising the respiratory rate (10 breaths/min). After a 30 min hyperventilation period, the second set of measurements was recorded. RESULTS: Acute hyperventilation induces an increase in Pv-aCO2 (from 3.87 ± 1.31 to 8.44 ± 1.81 mmHg, P < 0.001) and a decrease in ScvO2(from 71.78 ± 4.82 to 66.47 ± 5.74%, P < 0.001). The CO2GAP-Ratio was significantly increased(from 0.97 ± 0.40 to 1.74 ± 0.46, P < 0.001), and the PI showed a remarkable decrease caused by acute hyperventilation(from 1.82 ± 1.14 to 1.40 ± 0.99，P = 0.04). Hyperventilation-induced ∆_Pv-aCO2 was negatively correlated with ∆PaCO2(r = -0.572, P<0.001). The change in ∆_PaCO2 was correlated with ∆_ScvO2(r = 0.450, P<0.001). However, the left ventricular outflow tract velocity time integral (LVOT-VTI) remained unchanged during hyperventilation. CONCLUSIONS: Acute hyperventilation induced an increase in oxygen consumption and decreased peripheral tissue perfusion in patients. For critical care patients, it is necessary to pay attention to the influence of hyperventilation on peripheral tissue perfusion indices and oxygen consumption indices.

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.

RéSUMé: OBJECTIF: La différence de pression partielle de dioxyde de carbone veineux versus artériel (gradient de CO2) a été rapportée comme étant un indicateur sensible d'un débit cardiaque adéquat. Nous avons tenté d'évaluer si le gradient de CO2 pouvait prédire les devenirs postopératoires défavorables après une chirurgie cardiaque. MéTHODE: Une étude rétrospective a été réalisée en se basant sur les dossiers de 5151 patients issus de notre base de données départementale ayant subi une chirurgie cardiaque entre le 1er janvier 2008 et le 31 décembre 2018. Les taux de lactate (mmol·L−1), la saturation en oxygène veineux central (ScVO2) (%), et la différence de dioxyde de carbone veineux versus artériel (gradient de CO2) ont été mesurés lors de l'admission en réanimation (ICU) et aux jours 1 et 2 après la chirurgie cardiaque. Les complications postopératoires suivantes ont été colligées : mortalité en réanimation, hémopéricarde ou tamponnade, arrêt cardiaque récupéré, insuffisance rénale aiguë, saignements majeurs, insuffisance hépatique aiguë, ischémie mésentérique et pneumonie. Le critère d'évaluation principal était la présence d'au moins une complication postopératoire. La régression logistique a été utilisée pour évaluer l'association entre ScVO2, taux de lactate et gradient de CO2 et les complications. Leur performance diagnostique a été comparée à l'aide d'une courbe ROC (receiver operating characteristic). RéSULTATS: Des complications sont survenues chez 1933 patients (38 %). Les paramètres de circulation extracorporelle (CEC) étaient semblables entre les groupes. Le gradient de CO2 était légèrement plus élevé dans le groupe « complications ¼ que dans le groupe « pas de complication ¼. Les taux de lactate artériels à l'admission, au jour 1 et au jour 2 étaient également légèrement plus élevés chez les patients ayant subi des complications. La différence de saturation en oxygène veineux central n'était pas significative entre les patients avec ou sans complications. L'aire sous la courbe ROC pour prédire les devenirs après la CEC pour le gradient de CO2 à l'admission, au jour 1 et au jour 2 était de 0,52, 0,55 et 0,53, respectivement. CONCLUSION: Après une chirurgie cardiaque avec CEC, le gradient de CO2 à l'admission en réanimation, au jour 1 et au jour 2 était associé aux complications postopératoires, mais sa performance diagnostique était médiocre.