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#1
Old 07-31-2013, 06:36 PM
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Femoral artery vs carotid artery?

I was watching a program about shark attacks today and one of the victims had both legs severed and died on the shore because he was losing so much blood from his femoral arteries.

I've always been curious about the femoral artery after seeing an episode of the X Files where Mulder was shot in the leg and almost died because his femoral artery was severed, and the police confrontation with the Boston bombers in which the transit police officer was hit in the femoral and lost nearly all of his blood got me more curious.

So which is worse to get hit in, the femoral or the carotid? I had always thought it was the carotid but you'll always hear some story about how someone's femoral artery was severed and they bled out in under a minute.

Also, in the case of the shark attack victim in which BOTH of his femoral arteries were bleeding, how long do you suppose it took him to completely bleed out? I got the impression that he was still alive by the time the EMTs got there, because they said that even the EMTs weren't able to stop the bleeding. Also, since both arteries were bleeding, how soon after being bitten would he have begun to feel the effects of blood loss (i.e. dizziness, unconsciousness, etc)? Mere seconds or longer?
#2
Old 07-31-2013, 07:00 PM
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If a carotid gets severed, you will lose consciousness more rapidly (due to blood pressure in the brain falling), and will probably bleed out quicker (due to higher blood pressure up the neck from the heart.
But the femoral is no slouch, either, and you can bleed out from a femoral in a matter of minutes (2-3 is often quoted). You may last 30 seconds before blacking out, though.
The way the artery is opened has an impact on bleeding, though. A straight cut across the femoral will allow the artery to retract and close off somewhat (the muscle structure of an artery ensures this), whereas an angled cut will remain open. The shark victim could have wounds that partially sealed and slowed down the bleeding. But he would also be coping with massive shock - it is hardly surprising he died.
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#3
Old 07-31-2013, 07:06 PM
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They're both major arteries (not unlike I-95).

You don't want to sustain major trauma to either.
#4
Old 07-31-2013, 07:29 PM
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It's easier to put a tourniquet on the femoral artery, just sayin'.
#5
Old 07-31-2013, 07:34 PM
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Originally Posted by chacoguy View Post
It's easier to put a tourniquet on the femoral artery, just sayin'.
Well, umm... yeah... but... it is easier, but is it easy? I had the impression the the femoral was surround by other gunk and would not compress easily.
#6
Old 07-31-2013, 08:21 PM
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I've read stories about paramedics (or, like, just good sams) plugging an open artery by shoving a finger into it. Ick...but if it saves a life, hooray.

Worth knowing, on the million-to-one chance that you may be nearby when it's needed.
#7
Old 07-31-2013, 09:40 PM
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As a forensic pathologist, I get asked these kinds of questions fairly often. As for this one, just off the top of my head (so to speak) the way that I would approach it is: About 20-25% of cardiac output (CO, or blood leaving the heart for any given time period) goes to the brain. Most of that goes through the carotids, with smaller amounts going through other vessels. Since there are 2 carotids, lets say about 10% of CO goes through one carotid. By contrast, the skeletal muscles at rest get about 15% of CO at most, and that's all of the muscles. (That % will go up a lot with activity, whereas the % to the brain stays pretty much constant) The legs, fed by the femoral arteries, have a lot of muscle, so to estimate let's say about 3/4 of the blood to muscle goes to the legs, and since there are two of them let's say in total 1/2 of 3/4 of 15% of CO goes to each leg (while at relative rest). So that comes out to......5-6%.

So, roughly, a femoral artery passes about half as much blood per unit time as a carotid artery.

As for how long it would take to "bleed to death"? The comparative short answer of course is it would take about half as long with the severed carotid than a severed femoral, and about the same amount of time with one severed carotid or two severed femorals.

But as for an estimated time: CO at rest is about 5 liters/min. That goes up substantially with activity and stress, and I think it's probably underestimating to double it, but that would give us a conservative estimate as well as the number 10 to work with, which is always easier. So a person would lose about 10 % of 10 liters (= 1 liter) of blood per minute through a severed carotid, and about half that much through a severed femoral. A person has about 70mL of blood per kg body weight, and so for a 100 kg person ( about 220 pounds), that comes out to 7 liters of blood. Well before 50% blood loss, it's lights out, but using 50% of 7, that's 3.5, and at 1 liter per min with the severed carotid, that's 3.5 mins. About 7 mins for the femoral.

I repeat these are rough estimates and they don't take into accounts things like efforts to stop the bleeding.
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Old 07-31-2013, 10:01 PM
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What si_blakely said plus number of other variables.


A question for the forensic pathologist, if he's still tuned in: I've heard that John Ritter died of a ruptured aortic aneurysm.....is it possible to save a person if their aorta should rupture ....not in the middle of surgery or anything where immediate intervention would be possible, but in a more conventional/natural setting. If my aorta ruptures in my home, which happens to be right next door to the hospital & police station, can I be saved?
#9
Old 07-31-2013, 10:18 PM
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Yes people do survive these things. It just depends on the size of the rupture and where it is. A small rupture that allows blood to leak into the sac around the heart, for example, can be fatal very quickly. A larger rupture that goes somewhere else may actually stop itself just due to the pressure of the hematoma itself.
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Old 07-31-2013, 10:29 PM
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Fascinating, thank you. I was thinking of it terms of complete bisection of the arteries, but as you point out, there are degrees. I would guess that in the case of a complete severance of the aorta (knife wound, e.g.), someone would bleed out before help would arrive?
#11
Old 07-31-2013, 10:30 PM
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The thing is, bleeding out isn't the only factor. If you are shot in your femoral artery, the damage is pretty much confined to your leg. But there's so much vital anatomy near the carotid artery, depending on the bullet's trajectory, you may be sustaining other life-threatening damage.
#12
Old 07-31-2013, 11:17 PM
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Quote:
Originally Posted by eightysix View Post
As a forensic pathologist, I get asked these kinds of questions fairly often...
So how bad is it to get nailed in the subclavian arteries?(Just curious because I read somewhere that the whole "He'll be ok, he only got shot in the shoulder" thing in movies is nonsense because there's a good chance you'd get hit in one of those hoses and that's still pretty bad.)
#13
Old 08-01-2013, 04:53 AM
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Originally Posted by notsoheavyd3 View Post
So how bad is it to get nailed in the subclavian arteries?(Just curious because I read somewhere that the whole "He'll be ok, he only got shot in the shoulder" thing in movies is nonsense because there's a good chance you'd get hit in one of those hoses and that's still pretty bad.)
The Master speaks ...
#14
Old 08-01-2013, 05:23 AM
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Originally Posted by Enola Gay View Post
Fascinating, thank you. I was thinking of it terms of complete bisection of the arteries, but as you point out, there are degrees. I would guess that in the case of a complete severance of the aorta (knife wound, e.g.), someone would bleed out before help would arrive?
Sometimes even with medical help right there but improperly equipped: punctures of the femoral are a common CoD for bullfighters (many rings aren't equipped to deal with that kind of wounds, which is like not having burns treatment in a distillery), the aorta is worse.

Last edited by Nava; 08-01-2013 at 05:24 AM.
#15
Old 08-01-2013, 09:15 AM
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Quote:
Originally Posted by notsoheavyd3 View Post
So how bad is it to get nailed in the subclavian arteries?(Just curious because I read somewhere that the whole "He'll be ok, he only got shot in the shoulder" thing in movies is nonsense because there's a good chance you'd get hit in one of those hoses and that's still pretty bad.)
I suppose you could run it through the same estimate rubric as above: if the legs get about 3/4 of the blood flow to the muscles, that leaves about 1/4 for the arms, neglecting in this estimate the smaller amount that would go to muscles of the torso. So each arm gets 1/2 of 1/4 or 1/8 of CO ( perhaps it's coincidence, but that 1/8 corresponds nicely with the " rule of 9s" for body surface burns). So that's about 2% of total cardiac output. So blood loss = roughly 200 mL/min. That comes to about 17 mins or so to bleed to death.

Again: estimates based on physiology, assuming complete transaction of the vessel, with free flow out the severed end, and no efforts to stop it.
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