New noninvasive methodology to measure cardiac output in veno-venous extracorporeal membrane oxygenation patients

Abstract

Introduction: Cardiac output (CO) measurement is vital in veno-venous extracorporeal membrane oxygenation patient population to evaluate oxygen delivery and to early identify right heart failure. Standard clinical methods like pulmonary artery thermodilution and transpulmonary thermodilution are known to be inaccurate in the veno-venous extracorporeal membrane oxygenation setting, especially at high levels of recirculation. Objective: The aim of the study was to develop a simple noninvasive method to measure CO in patients during veno-venous extracorporeal membrane oxygenation. Methods: A mathematical model was developed where CO was analyzed as a combination of two flows: oxygenated blood from extracorporeal membrane oxygenation and less oxygenated mixed venous blood. The system of two mass balance equations for oxygen saturations was introduced to calculate CO. The procedure included measurement of recirculation (ELSA Monitor Transonic Systems Inc. Ithaca, USA) and arterial saturation at two extracorporeal membrane oxygenation flows after temporary pump flow decrease. Mathematic modeling that utilized a crude Monte Carlo method was used to analyze theoretical errors in CO calculations from unknown behavior of venous saturation. The developed concept was retrospectively applied to clinical data archive of 17 adult patients on veno-venous extracorporeal membrane oxygenation that included 52 measurement sessions. Results: Mathematical modeling suggests that proportion of results with error 10% was between 86% and 100% if pre-oxygenated saturation was available and it was between 78% and 86% if pre-oxygenated saturation was not available. Application of two mass balance equation concept to clinical data suggests that as the decrease of the arterial saturation reaches 6% due to flow decrease, then CO calculations becomes highly reliable as 96% (2 standard deviations) of the results has a reproducibility within 6.4%. Conclusion: The mathematical model and clinical retrospective analysis demonstrates that the new methodology has the potential to accurately measure CO in veno-venous extracorporeal membrane oxygenation patients. The next step is validation in animal and clinical settings.