I would have thought that an air bubble gets popped and we move on. That the gas eventually dissolves and gets passed somehow.
So, what’s going on? Why does the heart stop so violently? It acts like there was an implosion on the inside…
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Perfusionist here! Rule number one of my job is NO BUBBLES. The true ELI5 here is that your brain has small vessels, bubbles can get stuck in these vessels, blocking blood. No blood to the brain = bad. Your heart also has some small vessels. No blood to the heart = bad.
Some more important detail, but not ELI5, “air” is mostly nitrogen which does not dissolve into blood as easily as CO2 or O2. Looking at solubility coefficients, nitrogen dissolves about half as well as oxygen, and CO2 about 20x better than oxygen. Bubble size also greatly impacts dissolution times since surface area and volume are not linearly related. In water, it takes 1-6 seconds for a 10 micrometer diameter bubble to dissolve. At 100 micrometers that time jumps to 100-600 seconds. The time increases even more considering a lodged bubble is more of an oblong shape than a perfect sphere. This is very patient dependent, but <15 micron diameter bubbles typically make their way through microvasculature without much issue. The boundary between gray and white matter in your brain is perfused with a lot of vessels in the 20-50 micron range, which is unfortunately right in that range of long dissolution times.
During cardiac surgery (the field I’m most familiar with) we know bubbles get into the brain, typically in the low double digit micrometer range. If a noticeable air emboli were to be pumped up into your cerebral arteries, the turbulence in the blood can break it up into many many devastating emboli, leading to permanent tissue damage. Not something you want in your thinking blob.
This is all just brain stuff. As someone mentioned before, venous air emboli can cause lung perfusion issues (although lungs are excellent at removing gas from the venous system). A very big bolus of air could “air-lock” the heart, causing a drastic decrease in cardiac output. Air down the coronary arteries can block perfusion to the myocardium effectively causing a heart attack. This last one happens pretty often in cardiac surgery, but we’re typically still supported on cardiopulmonary bypass, it’s easily noticeable on the EKG, and the surgeon can massage air out by hand right there.
I love talking about bubbles in medicine, so thank you for asking this question.
EDIT: It’s important to note the pulmonary and systemic circulation do not tolerate bubbles equally. If a bubble leaves the left side of your heart (beginning of systemic), the first vessels that blood flow perfuses are the coronary arteries and the head vessels. Very bad. Stoke, death, etc. as explained above.
Small bubbles in your venous system are *unlikely* to cause any issues, but if you ask me, it’s not great practice. A venous bubble will travel back to the right chambers of your heart and get pushed into your pulmonary system. Usually they’ll dissolve away there without a problem. “50cc” seems to be the accepted limit, but not a chance in hell I would let 50ccs into my circulation (several feet worth of IV tubing). Not sure where that number comes from…
It’s not too unusual to have an undiagnosed shunt between the right and left chambers of your heart (~1 in 6 adults have a patent foramen ovale, 1 in 3 have IPAVA shunts), meaning bubbles could potentially pass straight to the left side, ejecting to your head vessels. Funny enough, a common way to detect these opening is by injecting micro bubbles to the right side and watching an ultrasound to see if any end up on the left. Air-blood interface activates platelets, clotting, cytokine release, causes glycocalyx damage, and a bunch of stuff you generally don’t want. If you’re sitting upright, air can also travel retrograde up the SVC and work it’s way into cerebral vessels. Are you going to die from a small bubble in an IV? Probably not. There is, however, a fair bit of research suggesting it’s not a totally insignificant event, and bubble traps exist. Whenever I donate plasma and see a bubble coming back my way, I fold the line to shut off the pump and politely ask someone to clear it. I don’t knock nurses/other providers for saying it won’t hurt you, because that training is pretty standard throughout medicine, and no one is consciously ignoring problems. I don’t consider myself a lucky person (more in my profile about that), so it’s a risk I don’t care to take, and I’ll shout about this whenever I get a chance.
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