Estimating cardiac output based on gas exchange during veno-arterial extracorporeal membrane oxygenation in a simulation study using paediatric oxygenators

Abstract

Veno-arterial extracorporeal membrane oxygenation (VA-ECMO) therapy is a rescue strategy for severe cardiopulmonary failure. The estimation of cardiac output during VA-ECMO is challenging. A lung circuit ({dot{text{Q}}}Lung) and an ECMO circuit ({dot{text{Q}}}ECMO) with oxygenators for CO2 removal (mathop {text{V}}limits^{.}CO2) and O2 uptake (mathop {text{V}}limits^{.}O2) simulated the setting of VA-ECMO with varying ventilation/perfusion (mathop {text{V}}limits^{.}/{dot{text{Q}}}) ratios and shunt. A metabolic chamber with a CO2/N2 blend simulated mathop {text{V}}limits^{.}CO2 and mathop {text{V}}limits^{.}O2. {dot{text{Q}}}Lung was estimated with a modified Fick principle: {dot{text{Q}}}Lung = {dot{text{Q}}}ECMO × (mathop {text{V}}limits^{.} CO2 or mathop {text{V}}limits^{.}O2Lung)/(mathop {text{V}}limits^{.}CO2 or mathop {text{V}}limits^{.}O2ECMO). A normalization procedure corrected mathop {text{V}}limits^{.}CO2 values for a mathop {text{V}}limits^{.}/{dot{text{Q}}} of 1. Method agreement was evaluated by Bland–Altman analysis. Calculated {dot{text{Q}}}Lung using gaseous mathop {text{V}}limits^{.}CO2 and mathop {text{V}}limits^{.}O2 correlated well with measured {dot{text{Q}}}Lung with a bias of 103 ml/min [− 268 to 185] ml/min; Limits of Agreement: − 306 ml/min [− 241 to − 877 ml/min] to 512 ml/min [447 to 610 ml/min], r2 0.85 [0.79–0.88]). Blood measurements of mathop {text{V}}limits^{.}CO2 showed an increased bias (− 260 ml/min [− 1503 to 982] ml/min), clinically not applicable. Shunt and mathop {text{V}}limits^{.}/{dot{text{Q}}} mismatch decreased the agreement of methods significantly. This in-vitro simulation shows that mathop {text{V}}limits^{.}CO2 and mathop {text{V}}limits^{.}O2 in steady-state conditions allow for clinically applicable calculations of {dot{text{Q}}}Lung during VA-ECMO therapy.