Comment on: “A novel ‘shunt fraction’ method to derive native cardiac output during liberation from central VA ECMO” by Lim, HS

• Published in: ESC Heart Failure Vol. 11; no. 4; pp. 2464 - 2466
• Main Authors: Bachmann, Kaspar F., Haenggi, Matthias, Jakob, Stephan M., Takala, Jukka, Gattinoni, Luciano, Berger, David
• Format: Journal Article
• Language: English
• Published: England John Wiley & Sons, Inc 01.08.2024; John Wiley and Sons Inc; Wiley
• Subjects: Accuracy; Extracorporeal membrane oxygenation; Gas flow; Hypoxia; Letter to the Editor; Lungs; Pulmonary arteries
• ISSN: 2055-5822; 2055-5822
• DOI: 10.1002/ehf2.14804

Monitoring of gas exchange estimates native cardiac output with acceptable precision and accuracy. 6 Based on our work, we conclude the following and would like to highlight certain limitations regarding Lim's method. 1 First, our method does not limit itself to states of no sweep gas flow (i.e. building an artificial right–left shunt). [...]our previous experimental data demonstrate that both venous and arterial differential hypoxia are present during VA ECMO. 6 While differential hypoxia on the arterial side is a known phenomenon (e.g. Harlequin or North–South), venous differential hypoxia is as common and important to managing patients on VA ECMO, albeit less often recognized. 3,7 The method is only accurate if and only if the inlet and outlet conditions of both the ECMO and the native lung are perfectly mixed; that is, there is no venous and arterial differential hypoxia. 5,6 Lim acknowledges the limitations of venous oxygen differences but suggests assuming a pulmonary vein (or left atrial) saturation of 100% to obviate the need for direct blood sampling and advises caution for critically ill patients with his assumption. Alternative approaches to the assessment of native cardiac output during VA ECMO may include modified thermodilution, which would also allow the evaluation of right ventricular performance. 8 We highly welcome further studies within the field of gas exchange and extracorporeal support and commend Lim for his work.