## Background

Parallel circulation represents a unique physiologic state in children with functionally univentricular cardiac anatomy characterized by the arterial saturation being a weighted average of the pulmonary venous and systemic venous saturation leaving circulation at increased risk for developing inadequate systemic oxygen delivery. The primary aim of study was to utilize pre-Glenn catheterization data to determine the association of different hemodynamic variables on oxygen extraction ratio. Secondary aims included determining the association of hemodynamic variables on superior vena cava (SVC) saturation and pulmonary to systemic blood flow ratio (Qp:Qs).

## Methods

This was a single-center, retrospective study using data from children with parallel circulation prior to Glenn procedure between 2017–2020. Correlation analyses using spearman correlation were conducted between all the variables of interest to survey potential correlations. A linear regression analysis was conducted to model the oxygen extraction ratio using variables noted to have a statistically significant correlation. Receiver operator curve analyses were conducted for variables with a p-value of less than 0.20 and binary variables were created for the predictors that had an area under the curve of greater than 0.70. Separate regression analyses were conducted for each with either SVC saturation or Qp:Qs as dependent variable. Independent variables were identified based on the factors found to have a statistically significant correlation with the dependent variable from the initial spearman correlation analyses.

## Results

A total of 45 patients were included in the final analyses. Median oxygen extraction ratio was 32.0% and it significantly increases as SVC saturation decreases, systemic blood flow decreases, total cardiac output decreases, Qp:Qs increases and systemic vascular resistance increases. Regression analyses with oxygen extraction ratio as the dependent variable demonstrated that systemic blood flow, SVC saturation, and Qp:Qs were significantly associated with oxygen extraction ratio. Regression analysis with SVC saturation as the dependent variable demonstrated that systemic arterial saturation, systemic blood flow and hemoglobin were significantly associated with SVC saturation:

## Conclusion

Oxygen extraction ratio in parallel circulation is significantly associated with systemic blood flow, SVC saturation, and Qp:Qs. SVC saturation is further associated with systemic arterial saturation and hemoglobin while Qp:Qs is associated with systemic vascular resistance, pulmonary vascular resistance, and pulse pressure. Understanding of these factors can help guide clinical monitoring and management strategies for this high-risk circulation.