The ED ECMO crew left the www.edecmo.org World Headquarters in May 2014 to meet with Dr. Jim Manning at the University of North Carolina Chapel Hill to do some animal experiments incorporating ECMO. Dr. Manning is an Emergency Department attending physician at UNC-Chapel Hill and has a distinct interest in endovascular resusscitation. Specifically, Jim is working with a new catheter called the “Selective Aortic Arch Perfusion” (or SAAP) catheter in non-compressible abdominal and pelvic trauma. The SAAP catheter functions much like REBOA (resuscitative endovascular balloon occlusion of the Aorta) and we will compare and contrast those two technologies in the near future.
Dr. Manning's expertise in animal models of resuscitation drew us to North Carolina. The experience was far beyond anything we could have expected and much much more will be posted over the coming months!
“PRIME TIME!” ~Nuances of priming the ECMO circuit with Greg Griffin, the Chief Perfusionist at UNC-Chapel Hill
The folks at UNC-Chapel Hill have a very active inpatient ECMO program. While they aren't yet doing ECPR in the ED (and we hope to help change that!), they do a lot of ECMO. Greg Griffin has been the Chief Perfusionist at UNC-Chapel Hill for the past 3 years and has been a perfusionist at their facility for over 20 years. While in Dr. Manning's lab, Zack had the opportunity to sit down with Greg and talk in depth about ECMO, the Maquet Cardiohelp ECMO machine, and some pearls and pitfalls of “priming the pump!”
- The ECMO circuit consists of:
- The machine: which is basically a centrifugal pump (a machine that generates forward blood flow via centrifugal force), an oxygen supply, and a water bath to control the temperature. Simple.
- The circuit: the circuit is a.) the tubing that the blood flows through, b.) a membrane oxygenator (a small plastic box that contains a membrane…blood flows across that membrane while oxygen is added to the blood and CO2 is removed), and c.) the pump head (a plastic chamber that transfers the centrifugal forces from the pump to generate forward blood flow).
- The combination of the tubing, oxygenator and pump head are also referred to as the “disposables,” because they come into contact with the patient's blood, and are later disposed of.
- The cart: which is the support structure that holds all the equipment.
- Priming the circuit = filling the entire circuit with fluid. Priming is done by hanging the fluid higher than the circuit and letting gravity fill the entire circuit. At the present time, we prime with a crystalloid solution.
- De-Airing: removing all air bubbles from the circuit. The nuances of this are discussed in this episode.
The Formula One Racetrack Analogy
- When the circuit is set up and the pump is flowing, a maze of tubes seems to spread haphazardly about the machine. What appears complicated and confusing is really quite simple: The circuit is nothing more than a big oval tube with blood flowing around the oval, not unlike an oval auto racetrack. When priming the pump you run the “cars” through the oval until you are ready to initiate bypass and add your patient to the circuit. Priming involves filling the circuit with fluid and de-airing the entire system.
- When it comes time to put your patient on bypass, you divert the “cars” from the “racetrack” and have them take a detour into the “pit,” which is your patient. Oxygenated blood that has just left the oxygenator exits the oval “racetrack” via detour-tubing, enters the arterial cannula, and enters the patient's arterial system. Deoxygenated venous blood that is returning to the heart is captured by the venous cannula (who's tip is at the right atrial inlet) and directed back onto the “racetrack”. The circuit once again passes the blood through the centrifugal pump (generating forward blood flow) and then, again, through the oxygenator.
- At any time you can elect to run your “race cars” through the circuit only (staying on the track), or through your patient. One or the other…but not both at the same time.
In keeping with the “North Carolina” theme, here is the Charlotte Motor Speedway in Charlotte, North Carolina:
Now, lets take another look at a diagram of the whole circuit: