Veno-arterial extracorporeal membrane oxygenation therapy is a growing treatment modality for acute cardiorespiratory failure. Cardiac output monitoring during veno-arterial extracorporeal membrane oxygenation therapy remains challenging. This study aims to validate a new thermodilution technique during veno-arterial extracorporeal membrane oxygenation therapy using a pig model.
Sixteen healthy pigs were centrally cannulated for veno-arterial extracorporeal membrane oxygenation, and precision flow probes for blood flow assessment were placed on the pulmonary artery. After chest closure, cold boluses of 0.9% saline solution were injected into the extracorporeal membrane oxygenation circuit, right atrium, and right ventricle at different extracorporeal membrane oxygenation flows (4, 3, 2, 1 l/min). Rapid response thermistors in the extracorporeal membrane oxygenation circuit and pulmonary artery recorded the temperature change. After calculating catheter constants, the distributions of injection volumes passing each circuit were assessed and enabled calculation of pulmonary blood flow. Analysis of the exponential temperature decay allowed assessment of right ventricular function.
Calculated blood flow correlated well with measured blood flow (r2 = 0.74, P < 0.001). Bias was −6 ml/min [95% CI ± 48 ml/min] with clinically acceptable limits of agreement (668 ml/min [95% CI ± 166 ml/min]). Percentage error varied with extracorporeal membrane oxygenation blood flow reductions, yielding an overall percentage error of 32.1% and a percentage error of 24.3% at low extracorporeal membrane oxygenation blood flows. Right ventricular ejection fraction was 17 [14 to 20.0]%. Extracorporeal membrane oxygenation flow reductions increased end-diastolic and end-systolic volumes with reductions in pulmonary vascular resistance. Central venous pressure and right ventricular ejection fractions remained unchanged. End-diastolic and end-systolic volumes correlated highly (r2 = 0.98, P < 0.001).
Adapted thermodilution allows reliable assessment of cardiac output and right ventricular behavior. During veno-arterial extracorporeal membrane oxygenation weaning, the right ventricle dilates even with stable function, possibly because of increased venous return.
Veno-arterial extracorporeal membrane oxygenation is an accepted rescue therapy for patients experiencing severe cardiac or pulmonary failure.
Weaning from veno-arterial extracorporeal membrane oxygenation is important for determining next steps in patients’ cardiopulmonary care. Assessment of right ventricular function during veno-arterial extracorporeal membrane oxygenation support and weaning is often done using echocardiography, but echocardiographic guidance provides challenges because right ventricular dimensions change with ventricular loading and may not be related to intrinsic right ventricular function.
In 16 healthy pigs that received veno-arterial extracorporeal membrane oxygenation support via central cannulation, a novel adaptation of thermodilution cardiac output assessment provided reliable estimation of right ventricular cardiac output and right ventricular function.
Future studies appear warranted to determine whether this method of modified thermodilution can be used to accurately assess right ventricular output and function during veno-arterial extracorporeal membrane oxygenation support.