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 (Q ˙ Lung) and an ECMO circuit (Q ˙ ECMO) with oxygenators for CO2 removal (V. CO2) and O2 uptake (V. O2) simulated the setting of VA-ECMO with varying ventilation/perfusion (V. /Q ˙) ratios and shunt. A metabolic chamber with a CO2/N2 blend simulated V. CO2 and V. O2. Q ˙ Lung was estimated with a modified Fick principle: Q ˙ Lung = Q ˙ ECMO × (V. CO2 or V. O2Lung)/(V. CO2 or V. O2ECMO). A normalization procedure corrected V. CO2 values for a V. /Q ˙ of 1. Method agreement was evaluated by Bland–Altman analysis. Calculated Q ˙ Lung using gaseous V. CO2 and V. O2 correlated well with measured 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 V. CO2 showed an increased bias (− 260 ml/min [− 1503 to 982] ml/min), clinically not applicable. Shunt and V. /Q ˙ mismatch decreased the agreement of methods significantly. This in-vitro simulation shows that V. CO2 and V. O2 in steady-state conditions allow for clinically applicable calculations of Q ˙ Lung during VA-ECMO therapy.