Patients receiving circulatory support with peripheral veno-arterial extracorporeal membrane oxygenation (VA-ECMO) are at risk of developing differential hypoxia. This phenomenon occurs in patients with concomitant respiratory failure. Poorly oxygenated blood, ejected into the ascending aorta from the left ventricle, competes with retrograde flow from the ECMO circuit, potentially causing myocardial and cerebral ischaemia. In a recent Critical Care article, Hou et al. use an animal model of peripheral VA-ECMO to study the physiology of differential hypoxia. Their findings support a dual circuit hypothesis, and show how different cannulation strategies can disrupt the two circuits. In particular, strategies that increase venous oxygen saturations in the pulmonary artery can have a large effect on oxygenation saturation in the ascending aorta. The authors provide evidence supporting the use of veno-arterial-venous ECMO in patients who require peripheral VA-ECMO but have simultaneous respiratory failure.
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