Does measuring veno-arterial carbon dioxide difference compare to predicting a hockey game's final score?

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.

Veno-Arterial Partial Pressure of Carbon Dioxide Difference as a Metric of Systemic Oxygen Delivery: Insights from a Correlative Meta-Analysis

The assessment of cardiac output and adequacy of systemic oxygen delivery in children after cardiac surgery require the use of an aggregate of hemodynamic monitors and blood tests. There are previously published data regarding the utility of the veno-arterial partial pressure of carbon dioxide difference (AVDco2) to help with this. This study pooled data on the correlation of AVDco2 with other metrics of cardiac output and systemic oxygen delivery such as arteriovenous oxygen saturation difference, venous saturation, and serum lactate. A systematic review of the literature was done to identify studies analyzing the correlation of AVDco2 with other hemodynamic and laboratory values. Data were extracted, and correlation coefficients were pooled for each specific comparison to create a point estimate for the overall correlation. A total of four studies with 350 patients and 809 paired blood gases were pooled. Adequate data were available to assess the correlation of AVDco2 with arteriovenous oxygen saturation difference, venous saturation, and serum lactate. There was a significant, moderate correlation with arteriovenous oxygen saturation difference and venous saturation. A significant, weak correlation with serum lactate was found. The AVDco2 has significant, moderate correlations with other metrics of the adequacy of systemic oxygen delivery such as arteriovenous oxygen saturation difference and venous saturation. There was a significant but only weak correlation with serum lactate. AVDco2 may be complementary to assess the adequacy of cardiac output and systemic oxygen delivery.

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 .