As a cardiac anesthesiologist, I see plenty of patients on ECMO (extra-corporeal membrane oxygenation). It’s a rapidly expanding life-saving technology that was almost unheard of when I was in medical school, but now it’s being deployed with greater and greater frequency.
ECMO came into the public eye during the COVID-19 pandemic outbreak in 2020, and has been featured on the “medical drama for people in medicine:” The Pitt.
If you’re a medical student now, there’s a good chance you’ll come across a patient on it. We’re going to review what the technology entails, so you’re prepared for any such encounter.
Here’s what you need to know about ECMO.
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ECMO Basics: Demystified
First, ECMO is a mechanical circulatory support (MCS) device. That means it helps the heart and lungs out when they’re unable to function properly.
All ECMO circuits operate on the same basic premise, but there are some fundamental distinctions among the different platforms we’ll discuss here, so that you can elevate your consciousness on this amazing technology!
To understand what ECMO does, simply break down the nomenclature:
EC or “Extracorporeal” means that ECMO operates outside of the body. This differentiates it from other MCS devices that work inside of the body, like Impellas, LVADs, and RVADs.
The next part is MO for “membrane oxygenation.” That simply means ECMO has a special membrane that provides oxygen to the blood.
It’s all about the pump!
Knowing that ECMO acts as a pump is a huge part of putting the puzzle together and understanding what the technology does and how it works. The pump can match the cardiac output necessary to perfuse a patient’s organs.
By adjusting its speed, a certain flow (think 3-6 liters per minute) can be achieved to suck blood into the ECMO circuit and deliver it back to the patient’s body.
More ECMO Basics: The Two Main Platforms
The two main platforms of ECMO to concern yourself with are VV ECMO (venovenous) and VA ECMO (venoarterial). Let’s take a look at each, so you can get a better understanding of these key elements of the technology.
1. VV ECMO (Venovenous)
VV ECMO sucks blood from a major vein in the patient’s body, delivers it to the membrane oxygenator pump, and sends it back into the patient’s venous system, fully oxygenated.
But that’s only half the story.
VV ECMO has a special function, colloquially known as “sweep,” which allows the system to eliminate carbon dioxide from the blood, helping to restore a sought after pH balance. It’s used when a patient’s lungs aren’t working properly, to oxygenate the blood and remove carbon dioxide from it.
2. VA ECMO (Venoarterial)
VA ECMO still removes venous blood from a patient, but after oxygenation and removal of carbon dioxide, blood is returned to the arterial system, usually via the femoral artery or directly into the aorta. Therefore, it bypasses the lungs and the heart.
This platform is used when a patient’s heart is too weak to circulate blood through their body and perfuse their organs.
ECMO Complications
Naturally, it takes some very large tubes in major veins and arteries to be able to move that much blood out of the body and back into it. Large cannulas make large holes. Ergo, vascular injuries and bleeding are major complications to look out for.
Bleeding is especially common as the circuits themselves can shear platelets, leading to coagulopathy. On top of that, the patient’s blood needs to be anticoagulated to prevent formation of thrombus (clots) in the tubing or oxygenator.
The Clinical Benefits of ECMO
The magic of ECMO is that it can do the work of a patient’s ailing organs (i.e., heart and lungs), in order to keep the rest of their organs (brain, gut, kidneys) happy. With the pressure off, the body’s natural recovery process (as well as pharmacological-induced recovery) can take place.
That’s why ECMO is a temporary solution to big picture problems. While some patients in the literature have spent more than a year on ECMO, it’s a bridge to recovery.
VV ECMO can be used while treatment takes place for severe lung disease (e.g., COVID, pneumonia, ARDS) and VA ECMO can be used to rest the heart when it’s unable to function well, like during a heart attack or immediately after cardiac surgery.
ECMO Basics: A Pearl of Wisdom
Entire textbooks have been written on ECMO and other forms of MCS. If you find it fascinating, there’s a nearly endless fund of knowledge to dive into. But understanding the ECMO basics will help you approach your next ECMO patient in the ICU with confidence and understanding.
I’ll end with a pearl of wisdom that bears repeating: reading about ECMO platforms will only serve part of your purpose. Once you round on an ECMO patient in the cardiac ICU or see an arresting patient get “put on ECMO,” the principles will be much easier to internalize and understand.
Reading is a necessity, but it isn’t a substitute for proper clinical experience!
Here’s a vignette to advance your knowledge on this subject:
A 58-year-old man with a past medical history of type 2 diabetes and mild COPD presents to the ED with refractory tachypnea, increased work of breathing, and hypoxia. Room air SpO2 is 82% and improves to 84% on BiPAP. The decision is made to intubate.
The first arterial blood gas shows a pAO2 of 40mmHg and a pACO2 of 37mmHg. CT chest shows diffuse ground glass opacities bilaterally, interstitial edema, and bilateral pleural effusions. Initial ventilator settings are FiO2 100%, RR 16, TV 500, PEEP 5.
Which of the following measures should be used to treat this patient’s hypoxia?
A) Increase respiratory rate.
B) Increase tidal volume.
C) Initiate extracorporeal membrane oxygenation.
D) Increase PEEP.
E) Initiate prone positioning.
The answer here is D. Increase PEEP.
The patient does not need a change in minute ventilation, as evidenced by their normal pACO2. However, their poor oxygenation will need intervention in order to deliver oxygen to the organs. While at some point they may need to be positioned prone, or even require ECMO if things worsen, easier, less invasive measures should be employed. Increasing PEEP will recruit more alveoli to participate in gas exchange, improving V/Q mismatch, and improving oxygenation.
Further Reading
Want to keep the learning going? Check out these other (free!) posts on the Blueprint blog:
