Electrical Impedance Tomography Reveals Venoarterial Extracorporeal Membrane Oxygenation Flow-Induced Ventilation-Perfusion Mismatch

Abstract

An obese female patient with ischemic cardiomyopathy was placed on venoarterial extracorporeal membrane oxygenation (VA-ECMO) for cardiogenic shock after in-hospital cardiac arrest. Despite biventricular recovery by day 3, VA-ECMO weaning was deferred due to persistent severe hypoxemia. To investigate cardiopulmonary pathophysiology, electrical impedance tomography (EIT) assessment was performed. Electrical impedance tomography-guided positive end-expiratory pressure (PEEP) titration confirmed that set PEEP minimized lung collapse, reducing the likelihood that intrapulmonary shunt was the primary cause of hypoxemia. With ventilator settings unchanged, EIT-based lung perfusion was assessed at VA-ECMO blood flows of 4.2 and 2.0 L/min. At lower (2.0 L/min) VA-ECMO blood flow, ventilation/perfusion (V/Q) matching significantly improved, primarily due to increased transpulmonary blood flow, which was redistributed from dorsal to ventral regions. Thus, by bypassing pulmonary circulation, higher VA-ECMO blood flow worsened V/Q mismatch and significantly contributed to hypoxemia. With these insights and after a successful weaning trial the next day, VA-ECMO was removed, and extubation followed 10 days later. To our knowledge, this is the first report of EIT enabling bedside assessment of the impact of VA-ECMO on regional lung perfusion, revealing an underrecognized iatrogenic contributor to hypoxemia. These findings underscore the distinctive value of EIT in tailoring cardiorespiratory care for VA-ECMO patients.