LAUSR

We read with great interest the recent paper by Buchtele et al. who describe a new technique to detect the watershed in peripheral veno-arterial extracorporeal membrane oxygenation (VA-ECMO) [1]. We would like to make some comments. Venous cannulation for VA-ECMO is usually performed through a femoral vein and the tip of the cannula placed in the inferior caval vein or lower part of the right atrium [2]. Blood leaving the ECMO circuit is normally fully saturated with oxygen, but usually only reaches body regions supplied by the descending aorta and the distal aortic arch in peripheral cannulation, as can be shown clinically by comparing pulse oximetry saturations [2]. In a simulation study combined with a case report, changing the venous cannulation site from the inferior to the superior caval vein was shown to increase arterial saturation in the right arm from below 60% to above 80% [2]. The authors of the study concluded that venous drainage from the superior caval vein improves upper body arterial saturation during veno-arterial ECMO as compared with drainage solely from the inferior caval vein in patients with respiratory failure [2]. The main finding of their simulation study was that arterial saturations are highly dependent on the venous cannulation site during VA-ECMO in patients with severe respiratory failure [2]. Venous drainage from the superior caval vein is preferred in VA-ECMO if hypoxic respiratory failure is present [2]. This situation can be achieved easily by inserting a venous cannula through the jugular vein with a high atrial tip position or a long and wide femoral venous cannula without side holes reaching the upper part of the right atrium [2]. Our question is as follows: should we pay more attention to detecting the watershed or should we focus on applying better cannula configurations [3] in order to avoid the Harlequin syndrome as much as possible? We believe that we should apply better cannula configurations.