Thanks to Fenton McCarthy, cardiac surgery fellow, for an incredible talk on extracorporeal membrane oxygenation (ECMO) and to everyone in the audience for creating a robust discussion.
We highlighted big differences between ECMO and cardiopulmonary bypass:
1) Cardiopulmonary bypass is a modality used almost exclusively for short periods of time in the OR
2) While similar, bypass circuits have a blood reservoir whereas ECMO circuits don’t
There are two main flavors of ECMO:
- Veno-arterial (VA) ECMO (see below): used if you have a cardiac problem (cardiac arrest, myocarditis, MI, cardiomyopathy, post-cardiac surgery) to provide circulatory support
VA ECMO: blood drains from a vein, gets oxygenated, and pumped back into an artery. It flows retrograde from the femoral artery up the aorta. Poorly oxygenated blood being pumped by the failing heart can mix with well-oxygenated retrograde blood from the ECMO catheter, creating differential regional hypoxemia, also known as “North South syndrome”
2. Veno-venous (VV) ECMO (see below): used primarily for respiratory failure (refractory hypoxemia, ARDS, etc). Complications are much less common with VV ECMO than VA ECMO.
VV ECMO: blood is drained from the SVC or IVC and returned to the venous system.
With VV ECMO, catheters can either go into the internal jugular vein or femoral vein. There’s also a catheter called an Avalon catheter (google it!) which is a single ‘catheter within a catheter’ that only requires placement of a cannula in the right IJ, and even permits ambulation!
We talked about some contraindications to ECMO (malignancy, unrecoverable neurological injury, age >75 among others, prolonged (>60 min) cardiac arrest, etc), and some tips for medicine residents if your patient is being considered for ECMO:
- Have one point person who knows the patient well be the one to talk to the ECMO fellow
- Get the unit charge RN involved early
- Get extra stuff (laundry carts, trash can, etc) out of the room to create space to work
The question always comes up: should I pre-emptively put in IJ or femoral central lines to make ECMO cannulation easier if things are headed that way?
The answer (as with so many things)is a little nuanced: if all they have is an IJ line, it’s advisable to put one in the other side because they will still need separate central access, and having to do so after they’ve been placed on ECMO comes with the theoretical risk of air embolism.
If groin ECMO access is being considered, you could put in bilateral femoral lines, but it really depends on the experience of the operator: to be helpful, the groin lines really need to be within 1-2cm of the groin crease.
How’s the evidence?
Lastly, we touched on the CESAR trial, which is really the only major/recent randomized trial that looked at whether ECMO has any benefit. The short answer: possibly yes, but it may not be a fair comparison because the ECMO group may have gotten better overall medical care than the ‘conventional therapy’ group
- Peek et al. CESAR: conventional ventilatory support vs ECMO for severe adult respiratory failure. PMC1766357
- Brodie D et al. ECMO for ARDS in adults. PMID 22316467
- Ventetuolo et al. Extracorporeal life support in critically ill adults. PMC4214087
A quick aside on hypothermia (the topic of our question-of-the-day)
Hypothermic patients can have sinus bradycardia, PVCs/PACs, atrial fibrillation and J-waves (also known as Osborne waves, see below). The height of the Osborne wave corresponds with the degree of hypothermia.
It is true that ‘you’re not dead until you’re warm and dead’. As the following NEJM table shows, hypothermia with hemodynamic instability is an indication to consider ECMO or cardiopulmonary bypass in order to speed rewarming:
Brown et al. Accidental hypothermia. NEJM. PMID 23150960.