Special ECMO Configurations:
LV Venting
This configuration usually arises when:
- A patient is on peripheral or central V-A ECMO but the left ventricle cannot eject adequately into the aorta, resulting in overdistention and pulmonary edema.
This can be corrected by decompressing the left ventricle, and there are several ways to achieve this:
- A second drainage cannula can be placed into the right atrium and across the interatrial septum, draining the left atrium of blood and joining the other return cannula in a "Y" configuration.
- A septostomy can be performed, creating a hole in the interatrial septum and allowing the LA to drain across into the right atrium, serving as a "pop-off valve".
- A second drainage cannula can be placed directly into the apex of left ventricle, joining the other return cannula in a "Y" configuration.
V-AV ECMO
This configuration usually arises when:
- A patient is on peripheral V-A ECMO for hemodynamic support and respiratory failure ensues causing hypoxemia.
- A patient on V-V ECMO for respiratory failure develops myocardial dysfunction and requires hemodynamic support (this is a less common reason at TGH).
The cannula are configured such that:
- There is one drainage cannula from a venous site.
- The return cannula is divided into a "Y" configuration, with one arm returning to the venous side and the other arm returning to the aorta.
VV-A ECMO
This configuration usually arises when:
- The high flows required through a single venous cannula cause significant hemolysis.
- Insufficient flows are obtained from a single cannula to provide the necessary hemodynamic support.
- Too much blood is entering the left ventricle causing distention and thrombosis (this is the most common reason at TGH).
The cannula are configured such that:
- There are two drainage cannulas connected via a "Y" configuration that connects to the oxygenator.
- Often the second drainage cannula is placed in the left atrium (sometimes called a left atrial "vent").
- A single return cannula delivers the blood into the aorta.
V-AV and VV-A configurations result in differential flow through the arms of the “Y” connector. These flows can be adjusted by altering the relative resistance between the two. This is usually accomplished by a mechanical clamp on one of the two arms.
Next page: ECMO Indications and Contraindications