Farhad Nezami, PhD
Hamed Moradi, Elazer R. Edelman, Steve P. Keller, Farhad R. Nezami*
Farhad R. Nezami
There exists a growing gap between the rising number of end-stage lung failure patients in urgent need of transplantation and availability of donated organs. The high mortality rate for this group of patients (almost 50%) mandates effective and safe strategies as a bridge to transplantation. Extracorporeal membrane oxygenation (ECMO) is increasingly being deployed as a life-saving means providing timely support for lung/heart failure patients. Despite the significant interest and use for ECMO, little is known about its interactions with the failing lung/heart and performance in perfusing vital organs. The optimal approach to particularly help patients with end-stage lung disease complicated by pulmonary hypertension or RV failure is not known. Recently, upper body venoarterial (VA) ECMO is being suggested through which, by shunting blood around the cardiopulmonary circulation, clinicians attempt to offload and improve the function of RV. Yet, in vivo studies of preclinical models have raised concerns about preferential perfusion of coronary arteries with native stream of low-oxygenated blood during ECMO therapy. We, for the first time, have developed a patient-specific computational tool to study upper body VA ECMO and titration of support on end-organ oxygen delivery. With varying ECMO-derived perfusion (2, 3, and 4 LPM), we modeled several scenarios with different partial pressure of oxygen for the compromised heart (30 and 60 mmHg) applying variable levels of oxygenation for ECMO supply (150, 300, and 500 mmHg). Results revealed that while a linear relation exists between organ oxygenation and the ECMO support oxygen content, increasing the ECMO flow had a non-linear effect on oxygenation. We conclude that the interplay between native and support streams and hemodynamic patterns majorly determine the efficacy of ECMO in helping patients and this is even more pronounced in lung failure patients wherein there is significant disparity in oxygen content of native heart and ECMO supply.
Based on computational simulations clinical remedies taken to overcome the ischemic risk in terms of increase in the partial pressure of oxygen from the support system would only be effective at higher flow rates of ECMO, wherein the retrograde support jet of highly oxygenated blood would overpower the antegrade native heart flow and reach the coronaries. Use of upper body VA ECMO should thus be limited to RV failure patients with sufficient lung function to be maintained with standard therapies for oxygen delivery (like HFNC). Close monitoring is required to ensure there is no progression to coronary ischemia, and further research is entailed to determine optimal support strategies for this population.