Extracorporeal membrane oxygenation (ECMO) provides temporary life-saving support for patients with severe cardiac failure, but is associated with significant morbidity and mortality. While ECMO enables oxygen delivery (DO₂), little is known about oxygen consumption (VO₂), largely due to technical difficulties. We aimed to introduce the adaptation of respiratory mass spectrometry to measure VO₂ in patients during ECMO and to use this unique model to determine the pathological dependency of VO₂ on DO₂ in humans.

Respiratory mass spectrometry remains the ‘state-of-the-art’ method, allowing the highly sensitive and rapid measurement of VO₂ in critically ill patients. The principle and design of the respiratory mass spectrometer are described, together with the setting up of this machine with the ECMO oxygenator and the native lungs of the patients. In two patients with severe dilated cardiomyopathy and little cardiac contraction, the decrease in pump flow and, hence, DO₂ by 20% was associated with a decrease in VO₂ by 5% and 8%, respectively, whereas the increase in pump flow was not associated with any significant change in VO₂.

The direct measurement of VO₂ by respiratory mass spectrometry in ECMO patients provides a unique technique for clinical research on the metabolism and VO₂-DO₂ relationship in this special group of critically ill patients. Our pilot study is the first to demonstrate a pathological dependency of VO₂ on DO₂ in humans. Further studies are warranted with this technique to examine the changes and the factors affecting systemic oxygen transport in patients during ECMO.