Clinical Case Scenario

A 62-year-old male with a history of hypertension and dyslipidemia presents to the emergency department with severe retrosternal chest pain, sweating, and shortness of breath. A 12-lead ECG was performed, suggesting ST-segment elevation Myocardial infarction (STEMI). The patient rapidly deteriorated, developing profound hypotension and signs of cardiogenic shock. The patient’s trachea was intubated and inotrope was started, however, the shock did not reverse and worsened. Due to refractory cardiogenic shock, veno-arterial extracorporeal membrane oxygenation (VA-ECMO) is initiated via the femoral artery and vein. Initial VA-ECMO support provides hemodynamic stability, and the patient is transferred to the intensive care unit (ICU).

Over the next few hours, the ICU team observes that the patient's lower extremities remain warm and well-perfused, with good oxygen saturation readings from the pulse oximeter. However, the patient's upper extremities and face exhibit cyanosis. Arterial blood gas analysis reveals a significant discrepancy with blood drawn from the radial artery (representing upper body oxygenation) shows a lower PaO2 whereas blood drawn from the femoral arterial line (representing lower body oxygenation from the ECMO circuit) shows a higher PaO2.

Wrong Answer: A. Differential oxygenation refers to a condition that can occur in peripheral (femoral) V-A ECMO (in the setting of femoral arterial reinfusion) in which the antegrade native cardiac output and ECMO reinfusion flow compete with each other. This results in a mixing point between the two flows. The position of the mixing point is dependent on the relative strengths of native heart pump and ECMO flows. Poor oxygenation of upper body is seen when mixing point is in the descending aorta.

Wrong Answer: B. Arterial blood gas (ABG) monitoring from right upper extremity is best way to determine differential oxygenation. Low oxygen tension on this ABG is suugestive of hypoxia in upper extremity subsequent to differential oxygenation.

Wrong Answer: C. Differential oxygenation is a feature of peripheral V-A ECMO. It is never seen in V-V ECMO.

Right Answer: D. Hybrid configuration with addition of a Y-connector to the arterial re-infusion cannula will help to overcome differential oxygenation. Addition of the Y-connector will help to split the blood flow between arterial reinfusion cannula (in femoral artery) and a venous reinfusion cannula (in right internal jugular vein returning blood to right atrium). This return of oxygenated blood to right atrium will help to improve oxygenation in upper extremity.