The Mode of ECMO is defined by where ECMO circuit blood is drained from the patient, where it is returned to, and the resulting physiological effects. The selection of the mode of support is based on the physiological needs of the patient.
Any mode of ECMO may be applied to a patient in different ways (different cannula types, different cannula tip positions and different insertion sites) but all share common physiological effects. See configurations and nomenclature sections.
Three Modes of ECMO are currently practiced at The Alfred:
- Veno-venous ECMO (VV ECMO): Blood is accessed from the venous side of the circulation (typically from great veins) and returned to the venous side of the circulation (typically to the right atrium). This mode provides support for respiratory failure by providing non-pulmonary gas exchange. Native cardiac function provides cardiac output and pulmonary blood flow.
- Veno-arterial ECMO (VA ECMO): blood is accessed from the venous side of the circulation (typically the right atrium), bypasses the pulmonary circulation and is returned to the arterial side of the circulation (aorta). This mode provides arterial circulation and organ perfusion despite native cardiac failure. This mode unloads right ventricular failure but does NOT unload left ventricular failure.
- Veno-pulmonary artery ECMO (VPA ECMO): blood is accessed from the venous side of the circulation (typically the right atrium) and returned to the pulmonary artery. This mode provides support for right ventricular failure and non-pulmonary oxygenation. Blood bypasses the right ventricle. Typically it is used to support transient right ventricular failure following insertion of a durable left ventricular assist device (LVAD).
Some patients require a transition from one mode of ECMO support to another over the duration of their illness. Under exceptional, complex circumstances, some physiological states may receive two ECMO modes configured in series or in parallel.
- Veno-venoarterial ECMO (V-VA ECMO or V-AV ECMO*): blood is accessed from the great veins and returned to BOTH the right atrium and aorta from a single pump and membrane oxygenator.(* See nomenclature)
- VV ECMO with VA ECMO (VV ECMO + VA ECMO): blood is accessed from the great veins, pumped by separate pumps (to separate membranes) and returned to BOTH the right atrium and aorta.
Veno-Arterial (VA ECMO)
VA support is the application of extracorporeal circulation primarily for cardiac or circulatory support, in which the extracorporeal circuit drains blood from the venous system and returns into the systemic arterial system.
VA support involves returning blood to the systemic arterial circulation, operating in parallel with the native circulation and provides partial or complete bypass of the heart and lungs. Although used primarily for cardiac support in selected circumstances, VA support can also be used for respiratory or combined cardiac and respiratory support.
Veno-Venous (VV ECMO)
Venous blood is accessed from the large central veins, pumped through the oxygenator and returned to the venous system near the right atrium. It provides support for severe respiratory failure where the circulation is entirely reliant on native cardiac function. It operates in series and does not provide bypass of the heart or lung. There are 4 main configurations of VV ECMO used at The Alfred.
- Femoro-Femoral (Fem/Fem)
- High-Flow (dual access)
- Femoro-Jugular (Fem/Jug)
- Dual lumen/Two stage single cannula (Avalon ELITEᵀᴹ Bi-Caval Dual Lumen Catheter)
In all cases, ECMO blood flow travels from the vena cavae to the atria (Cavo-Atrial Flow) to minimise recirculation. Significant recirculation manifests as a high venous saturation in the access limb AND low patient arterial blood saturations.
Combined ECMO modes
Combined modes refer to the delivery of two modes in parallel. For example Veno-venoarterial (V-VA) is a configuration of VV and VA extracorporeal support in which the extracorporeal circuit drains blood from the venous system and reinfuses into both the venous and systemic arterial systems. V-VA ECMO provides both pulmonary (VV component) and cardiac support (VA component) in patients with combined cardiopulmonary failure. This may occur in a patient supported with VA (1) with additional catastrophic pulmonary pathology (e.g. extensive chest haemorrhage in a transplant patient) or (2) where there is either recovery of heart function in the setting of pulmonary pathology that may require ‘transition’ to VV ECMO support.
Overall, this is a rare mode that should be carefully considered and presents additional physiological challenges.
Temporary RVAD or Veno-Pulmonary Artery (VPA) ECMO
Venous blood is accessed from a large central vein, pumped through the oxygenator and returned to the pulmonary arterial system. It provides short-term right ventricular and respiratory support typically following permanent LVAD insertion. The oxygenator does not necessarily need to be included in the circuit when the respiratory function is adequate; in which case the extracorporeal circuit is a temporary RVAD. The addition of the oxygenator (VPA ECMO or oxyRVAD) adds resistance to the circuit and may limit the desired flow rate. Decannulation can occur without the need for re-sternotomy.
Temporary BiVAD
In addition to a temporary RVAD, a BiVAD configuration consists of an additional circuit with a separate access from an apical LV cannula positioned in the mid-left ventricular cavity and a return to the proximal aorta. This may be used following conversion from an LV decompression cannulation or transition from VA ECMO to a longer VA ECMO support run.
Displayed is temporary BIVAD support in a patient with biventricular failure. The flows are roughly the same however vary with differing intrinsic function of each ventricle, valvular leakage, and measurement errors. Note how with almost the same RPM the RVAD pumps more blood returning into a low-pressure system.