Bubble Thrombosis: Fact or Fiction?

March 26, 2007 12:08 PM

Air bubble in the artery... we've seen the TV murder mystery where someone is killed by having air injected directly into their artery, resulting in heart failure. My question is how much air would it take? A little or a lot?
posted by lekvar to health & fitness (17 comments total)

About 200 CCs.
posted by mjbraun at 12:14 PM on March 26, 2007

Is this a hypothetical question or are you researching a novel?

Somewhat related, I recently learned that sterile water can be injected into a woman's back to decrease pain caused by back-labor during delivery.
posted by mattbucher at 12:16 PM on March 26, 2007

My uncle had to undergo chemotherapy for rectal cancer, which involved having a catheter in his arm that connected to his slow chemo-infuser thing. The catheter had to be flushed daily with a syringe of anti-clotting stuff. While my aunt and I were being taught how to do this, I noticed little air bubbles going into the catheter and asked the nurse the same question.

And yup, she said it would take a lot and those tiny bubbles won't be harmful.
posted by CKmtl at 12:22 PM on March 26, 2007

Yea, I was in the hospital recently and asked the same question as CKmtl. The nurse indicated about a foot-long length of the IV tubing...not a scientific measurement by any means, but reassuring nonetheless.
posted by cabingirl at 12:29 PM on March 26, 2007

My question comes from a situation similar to CKmtl's. My daughter just had her tonsils and adenoids out. After the procedure she was kept on an IV drip and her mother and I noticed a pretty sizable (not 200 cc's worth though) bubble creeping towards the catheter. We expressed our concern to the nurse and she explained that the bubble would diffuse in our daughter's bloodstream harmlessly. To her credit she recognized our discomfort and flushed the catheter tube with a minimum of eye-rolling, but I've been wondering since.
posted by lekvar at 12:31 PM on March 26, 2007

The usual answer is: Enough to de-prime the heart so that it couldn't pump.

I'd be scared of blood clots, most of all.
posted by cmiller at 12:39 PM on March 26, 2007

I think the issue is not with de-priming the heart as a pump, and more with the air bubbles blocking important arteries in the same way that clots can. As I understand it, thrombosis = artery blocked by a clot; embolism = artery blocked by anything. So a thrombus and a bubble are both types of emboli. IANAD, but I have been researching this stuff lately due to my own curiosity.

I'm very curious to hear from a real doctor on this question. I was under the impression that very small bubbles could cause problems, and was shocked to read mjbraun's linked answer of 200 CCs.
posted by vytae at 12:57 PM on March 26, 2007

This is a problem I often deal with for a variety of reasons; gas embolism in the broadest sense can occur during open-heart surgery as well as certain neursurgical and orthopedic procedures, laparoscopic surgery, and c-sections and it is also a concern during SCUBA diving. The amount of air needed varies greatly depending on several factors.

If the air is on the venous side of the circulation it takes a fair amount to kill someone but the exact amount depends on the speed of injection. Here is what a CT scan of 90 cc's of air in the heart and nearby vessels looks like. As cmiller pointed out this is generally a problem if it causes an airlock in the right side of the heart and pulmonary artery. If severe enough it can cause rapid cardiovascular collapse and death. Another problem for about 20-30% of the population is that they have a patent foramen ovale in their heart which can allow air to cross to the left side of the heart and become the much more dangerous arterial gas embolism. In this case as little as 1 cc of air in a coronary artery can cause a fatal heart attack; a similar amount in one of the blood vessels going to the brain can cause a stroke. This is more likely than chance would dictate because the heart and brain together get about 40% of the blood pumped by the heart.

Another factor in the seriousness of a gas embolism is the type of gas involved. Oxygen and carbon dioxide are very soluble in blood, and so emboli consisting of these gases need to be relatively large to cause problems as they get absorbed rapidly. This is one reason carbon dioxide is used to distend the abdoment during laparoscopic procedures. On the other hand, nitrogen (which is about 79% of the gas in air) is insoluble and so hangs around longer and causes more trouble.

To address the concerns of several posters above, the bubble in IV tubing are generally a fraction of a CC and so are not going to cause a problem. This is not true of many patients with congenital heart defects, however, as they may have abnormal communications between the right and left heart that will allow any venous air to potentially get into the arterial system. This is a question I get on a regular basis, so I am not surprised to see it raised here.

As you can see, this is not only real, but there is a lot of mdical literature on it. A search for venous gas embolism/arterial gas embolism will give you a lot more information (such as treatment) if you are interested. To answer your question on how much air, it can vary from 1 cc down a coronary artery to over a liter if injected slowly into a vein. 150-300 cc of venous air is commonly cited as a number to worry about, but as you can see that is just a generalization.
posted by TedW at 1:07 PM on March 26, 2007 [6 favorites has favorites]

TedW: Why doesn't the bubbly blood from the right side of the heart eventually make it to the left side of the heart, even if the person doesn't have a patent foramen ovale? Doesn't it all get pumped through both sides, eventually?
posted by vytae at 1:13 PM on March 26, 2007

I wish I could mark that as best answer twice. Thanks TedW.
posted by lekvar at 1:14 PM on March 26, 2007

As I understand it, thrombosis = artery blocked by a clot; embolism = artery blocked by anything

That is close, but not exactly right. Thrombosis means a blood clot, generally in a vessel; embolism means something in a blood vessel occluding it. Both can be either arterial or venous. An embolism can be a thrombus (as in thromboembolism), a bubble, or a foreign body (bullets are surprisingly common).
posted by TedW at 1:15 PM on March 26, 2007

Why doesn't the bubbly blood from the right side of the heart eventually make it to the left side of the heart, even if the person doesn't have a patent foramen ovale? Doesn't it all get pumped through both sides, eventually?

It does indeed get to the left side eventually, but it first goes through the lungs where any bubbles are filtered out in the capillary bed. In fact this exposure of all of the blood to one organ during each trip around the body is why the lungs have a number of functions beyond gas exchange.

Thanks for the compliment, lekvar; I guess you see I enjoy this sort of topic.
posted by TedW at 1:19 PM on March 26, 2007

Fascinating! Thanks to lekvar for asking, and thanks to TedW for helping me understand. You guys are great.
posted by vytae at 1:30 PM on March 26, 2007

Remind me never to piss off lekvar now that he knows how to kill a man without leaving evidence.

But that is the real question implied here - does it leave evidence? If someone managed to inject a victim with 200CC of air, would it look like natural causes or would Dr. Robbins get suspicious during the autopsy.
I'm just curious, nothing concrete planned...
posted by AndrewStephens at 2:56 PM on March 26, 2007

Previously on AskMeFi: What does air do to your heart?
posted by verstegan at 3:08 PM on March 26, 2007

Generally it will leave evidence such as microscopic hemorrrhages in the involved tissues, as well as the injection site in the scenario described. These may be subtle and possible to overlook, but if a young, healthy person died suddenly and there was no obvious reason, the medical examiner would be looking pretty agressively for subtle clues.
posted by TedW at 3:39 PM on March 26, 2007

Regarding leaving evidence:

I believe it was mjbraun's link at the top of the thread that said they can x-ray the body before autopsy to see the air in the vessels, if they suspect something. Then they have to do the autopsy very carefully, and dissect the vessels underwater to look for the telltale escaping bubbles, to avoid losing all the evidence as soon as they slice the guy open.
posted by vytae at 11:08 AM on March 27, 2007