Differential hypoxemia and the clinical significance of venous drainage position during extracorporeal membrane oxygenation

Background: Differential hypoxemia (DH) has been recognized as a clinical problem during veno-arterial extracorporeal membrane oxygenation (VA ECMO) although its features and consequences have not been fully elucidated. Purpose: This single center retrospective study aimed to investigate the clinical characteristics of patients manifesting DH as well as the impact of repositioning the drainage point from the inferior vena cava (IVC) to the superior vena cava to alleviate DH. Methods: All patients (>15 years) commenced on VA ECMO at our center between 2009 and 2020 were screened. Of 472 eligible patients seven were identified with severe DH. All patients had the drainage cannula tip in the IVC or at the junction between the IVC and right atrium. Results: The mean peripheral capillary saturation increased from 54 (+/- 6.6) to 86 (+/- 6.6) %, (p = <0.001) after repositioning of the cannula. Pre-oxygenator saturation increased from 62 (+/- 8.9) % prior to adjustment to 74 (+/- 3.7) %, (p = 0.016) after repositioning. Plasma lactate tended to decrease within 24 h after adjustment. Five patients (71%) survived ECMO treatment, to discharge from hospital, and were alive at 1-year follow-up. Conclusion: Although DH has been described in several studies, the condition has not been investigated in a clinical setting comparing the effect on upper body saturation before and after repositioning of the drainage cannula. This study shows that moving the drainage zone into the upper part of the body has a marked positive effect on upper body saturation in patients with DH.