Regional perfusion during venoarterial extracorporeal membrane oxygenation: a case report and educational modules on the concept of dual circulations

Abstract

A challenging aspect of managing patients on venoarterial extracorporeal membrane oxygenation (V-A ECMO) is a thorough understanding of the relationship between oxygenated blood from the ECMO circuit and blood being pumped from the patient's native heart. We present an adult V-A ECMO case report, which illustrates a unique encounter with the concept of "dual circulations." Despite blood gases from the ECMO arterial line showing respiratory acidosis, this patient with cardiogenic shock demonstrated regional respiratory alkalosis when blood was sampled from the right radial arterial line. In response, a sample was obtained from the left radial arterial line, which mimicked the ECMO arterial blood but was dramatically different from the blood sampled from the right radial arterial line. A retrospective analysis of patient data revealed that the mismatch of blood gas values in this patient corresponded to an increased pulse pressure. Having three arterial blood sampling sites and data on the patient's pulse pressure provided a dynamic view of blood mixing and guided proper management, which contributed to a successful patient outcome that otherwise may not have occurred. As a result of this unique encounter, we created and distributed graphics representing the concept of "dual circulations" to facilitate the education of ECMO specialists at our institution.

Keywords: ECMO, education, cardiopulmonary bypass, cannulation.

Figure 1.

Illustration of dual circulations during venoarterial extracorporeal membrane oxygenation (V-A ECMO). (A) Patient in cardiorespiratory failure. (B) V-A ECMO circulation. (C) Patient on V-A ECMO support showing the merging of circulations.

Figure 2.

Illustration of arterial blood mixing with central cannulation during venoarterial extracorporeal membrane oxygenation (V-A ECMO). (A) The absence of arterial blood mixing when the aortic valve remains closed. (B) The location of blood mixing when the left ventricle is ejecting.

Figure 3.

“Mixing cloud” phenomena during venoarterial extracorporeal membrane oxygenation (V-A ECMO) with peripheral cannulation. Shows the effects of left ventricular contractility and ECMO blood flow on the location of the “mixing cloud” within the aorta.

Figure 4.

Illustration of arterial blood mixing with central cannulation during venoarterial extracorporeal membrane oxygenation (V-A ECMO). (A) The absence of arterial blood mixing when the aortic valve remains closed. (B–D) The variable location of blood mixing when the left ventricle is ejecting.

Figure 5.

Hypothesized location of “mixing cloud” of case study patient.