Thermodilution is unreliable in veno-venous extracorporeal membrane oxygenation (VV-ECMO). Systemic oxygenation depends on recirculation fractions and ratios of extracorporeal membrane oxygenation (ECMO) flow to cardiac output. In a prospective in vitro simulation, this study assessed the diagnostic accuracy of a modified thermodilution technique for recirculation and cardiac output. The hypothesis was that this method provided clinically acceptable precision and accuracy for cardiac output and recirculation.
Two ECMO circuits ran in parallel: one representing a VV-ECMO and the second representing native heart, lung, and circulation. Both circuits shared the right atrium. Extra limbs for recirculation and pulmonary shunt were added. This study simulated ECMO flows from 1 to 2.5 l/min and cardiac outputs from 2.5 to 3.5 l/min with recirculation fractions (0 to 80%) and pulmonary shunts. Thermistors in both ECMO limbs and the pulmonary artery measured the temperature changes induced by cold bolus injections into the arterial ECMO limb. Recirculation fractions were calculated from the ratio of the areas under the temperature curve (AUCs) in the ECMO limbs and from partitioning of the bolus volume (flow based). With known partitioning of bolus volumes between ECMO and pulmonary artery, cardiac output was calculated. High-precision ultrasonic flow probes served as reference for Bland–Altman plots and linear mixed-effect models.
Accuracy and precision for both the recirculation fraction based on AUC (bias, −5.4%; limits of agreement, −18.6 to 7.9%) and flow based (bias, −5.9%; limits of agreement, −18.8 to 7.0%) are clinically acceptable. Calculated cardiac output for all recirculation fractions was accurate but imprecise (RecirculationAUC: bias 0.56 l/min; limits of agreement, −2.27 to 3.4 l/min; and RecirculationFLOW: bias 0.48 l/min; limits of agreement, −2.22 to 3.19 l/min). Recirculation fraction increased bias and decreased precision.
Adapted thermodilution for VV-ECMO allows simultaneous measurement of recirculation fraction and cardiac output and may help optimize patient management with severe respiratory failure.
- Veno-venous extracorporeal membrane oxygenation is a commonly performed rescue technique for patients experiencing severe respiratory failure
- While veno-venous extracorporeal membrane oxygenation improves the patient’s oxygenation, some patients remain with poor cardiac or respiratory function because of poor residual lung function, low cardiac index, and increased fraction of blood flow that recirculates within the extracorporeal membrane oxygenation circuit without passing through the lungs
- While thermodilution methods are the gold standard for measuring cardiac output in patients not on extracorporeal membrane oxygenation, these methods are not suitable for extracorporeal membrane oxygenation without adaption
- The authors built an in vitro simulator representing whole-body circulation and a veno-venous extracorporeal membrane oxygenator
- With this bench setup, the authors demonstrated that adapting the classical thermodilution technique with an additional temperature measurement at the extracorporeal membrane oxygenation inlet allows simultaneous cardiac output and recirculation assessment
- Translation to the bedside of this novel approach may help optimize extracorporeal membrane oxygenation and cardiac function during veno-venous extracorporeal membrane oxygenation
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