Extracorporeal Membrane Oxygenation Watershed
A 55-year-old, previously healthy man was admitted to another hospital with deep-venous thrombosis in both legs and massive pulmonary embolism verified by chest computed tomography (CT). He presented with severe dyspnea and hypotension refractory to inotropes. Fibrinolytic therapy with recombinant tissue plasminogen activator was initiated, but the patient further deteriorated and required cardiopulmonary resuscitation for a period of 30 minutes. After return of spontaneous circulation, he remained in cardiogenic shock despite the use of inotropes and vasopressors, which is why our hospital was contacted.
Our mobile extracorporeal membrane oxygenation (ECMO) team was dispatched and the patient received veno-arterial ECMO support with a 24 French venous cannula inserted via the right femoral vein and advanced into the right atrium and a 17 French arterial cannula inserted into the right femoral artery and advanced into the right iliacal artery. With an ECMO blood flow of 4.5 L/min, hemodynamics stabilized and the patient was transported to Hannover Medical School. Here, the patient was mechanically ventilated with an inspiratory oxygen fraction of 1.0 and the arterial PO2 measured in blood obtained from the right radial artery was >400 mm Hg. The mean systemic blood pressure was 90 mm Hg, but the arterial pressure curves were almost nonpulsatile, and echocardiography showed little contractions of both the right and the left ventricle.
Another CT scan performed approximately 14 hours after fibrinolysis showed persistent subtotal thromboembolic occlusion of the pulmonary vascular bed. In addition, there was an extensive filling defect in the ventral aspects of the ascending aorta (Figure 1). The left atrium, the left ventricle, and the aortic bulb were void of contrast material, whereas the aortic arch and the descending aorta were well contrasted (Figures 2 and 3).
These images demonstrated the so-called ECMO watershed, where well-contrasted blood coming from the ECMO circuit met low-contrasted blood coming from the left ventricle. The patient with his subtotally occluded pulmonary vascular bed and near complete loss of cardiac contractility had almost complete blood supply from the ECMO and very little regular blood flow. The ECMO device took up most of the contrast media, whereas only a small amount passed the pulmonary vascular bed. Hence, the aorta was filled mostly retrograde. Most of the aorta, including all 3 supraaortic vessels, received well-contrasted and well-oxygenated blood from the ECMO whereas the aortic bulb with the coronary arteries received noncontrasted blood coming from the left ventricle (Figures 2 and 3).
In patients receiving veno-arterial ECMO support, the term watershed describes the phenomenon that blood coming from the ECMO flows in the opposite direction than blood coming from the left ventricle.1,2 The level where these 2 blood streams meet (ie, the watershed) depends on the relative pressures and flows in both systems. The oxygen content of the blood coming from the left ventricle is unknown, posing a risk of profound hypoxemia to the heart and the brain when the watershed is located distal from the carotids. Blood gases obtained from the right radial artery reflect those delivered to the brain, but they may not necessarily reflect the oxygen content of the blood delivered to the coronary arteries. Thus, severe cardiac hypoxia may occur in patients receiving veno-arterial ECMO support. This problem was illustrated by the CT scans obtained in our patient, showing that the supraaortic branches were receiving blood from the ECMO circuit whereas the coronary arteries received blood coming from the left ventricle, which may have contributed to the severe cardiac dysfunction seen after the patient received ECMO support.
The patient underwent pulmonary thrombectomy a couple of hours after the CT scan was obtained. The postoperative course was uneventful. The patient was extubated 3 days after surgery and showed no neurological deficits. Cardiac function recovered within 6 days, after which the ECMO was removed.
To the best of our knowledge, this is the first visualization of the ECMO watershed in human, clearly illustrating a well-recognized phenomenon and underscoring the observation that blood gases obtained from radial arteries may not necessarily reflect the oxygen content in the coronary arteries.
Dr Hoeper has received honoraria for lectures and consultations from Actelion, Bayer, GSK, and Pfizer. The other authors report no conflicts.
- © 2014 American Heart Association, Inc.
- Field ML,
- Al-Alao B,
- Mediratta N,
- Sosnowski A
- Stulak JM,
- Dearani JA,
- Burkhart HM,
- Barnes RD,
- Scott PD,
- Schears GJ