Thread by @lindaschulteMD

For student coming onto #cardiacsurgery: here’s a primer on cardiopulmonary bypass I usually give between rounds and incision

You won’t pass perfusion boards from this 🧵but hopefully you’ll feel more oriented at the table.

#cardiotwitter #surged #meded #CTSurgery

When I was a sub-I on cardiac surgery I was totally lost on what all the different tubes did and would see a diagram like this and think I should stick to belly surgery:

But it’s not actually that complicated. Basic idea:
Bypass helps us overcome some unique challenges of operating on the heart:
🫀It’s full of blood
🫀It moves
🫀If it’s not moving, then something else needs to perfuse the body while we interrupt it from doing that

The solutions:
1. The venous cannula empties the heart
2. Cardioplegia (high potassium solution) stops the heart
3. The aortic cannula perfuses the body while we stop the heart

So for most basic cardiac surgery cases these are the components you need

To run blood through tubing then back to the body the patient needs to be fully heparinized: usually a dose that achieves an activate clotting time >450 seconds. Once we are ready to put in cannulas, we ask anesthesia to give “full dose heparin”

First step is placing the aortic cannula. When sticking things into the aorta: check that your blood pressure isn’t too high (over 110 systolic)

Next we add a venous cannula. Unless you’re working on the tricuspid or mitral valve, a single cannula in the right atrium works fine. At this point if the patient were struggling, you have enough to go on bypass.

Next we add a cannula for antegrade cardioplegia delivery: meaning the high potassium solution will flow forward through the coronaries. This goes below the aortic cannula so you can clamp in between.

Once on bypass, the venous cannula empties the heart to the venous reservoir, which then passes through a oxygenator and goes back to the patient through the aortic cannula. This is when anesthesia can turn the lungs off!

If we stop the heart, we need a way to keep the blood flowing to the body from coming back to the heart, and a way to keep the cardioplegia from running off to the body. This is the cross clamp.

The only thing missing now is suckers and vents. “Pump suckers” and “vents” return blood to the same place as the venous cannula: to the reservoir. So “bleeding” on bypass isn’t as concerning because it can be returned to the patient through the circuit.

What’s the difference between ECMO and cardiopulmonary bypass? The reservoir! This allows the perfusionist to control the amount of blood in the heart depending on how much they drain.

Once the cross clamp is on, the heart is stopped with cardioplegia and the real surgery begins.

Clamp time = ischemic time for the heart. The surgeon is usually in “go mode” so not a good time to ask questions 🙃

Once the surgery is done, the clamp comes off and the heart is woken back up until it is ready to “separate from bypass” - a topic for another day.

That’s the basics! Of course there are different permutations that make cardiac surgery a fun puzzle. As one of my mentors likes to say, cannulating and going on bypass is NOT the surgery, it’s the thing you have to do to DO the surgery.