Exsanguinate! Exsanguinate!

Dear Dr. Grasshopper,

How much blood can a character lose before they die?

Well, it kinda depends on the size of the character, to be honest. If a very large man loses a liter of blood, it’ll have a completely different effect than if a very small woman loses a liter. So the specific amount that a character can lose varies with the character. But I’ll try to give some general guidelines so you can figure it out for your character.

First of all, let’s figure out how much blood is actually in your character.

Blood is made of plasma, and blood cells, and all kinds of good stuff. (Remind me to write a post about blood composition.) Regardless, here’s a reasonable way to figure out how much blood your character is starting out with.

WARNING! MATH AHEAD! DON’T RUN AWAY; YOU WILL JUST HAVE TO DO THE CALCULATIONS TIRED! (PS: I suck royally at math, so if I screw up, please let me know.)

(Important terminology – “Hematocrit” = the percentage of blood volume occupied by red blood cells. Typically, around 47% in men and around 42% in women. Plus or minus a few percent.)

Okay, now that that’s out of the way, we can do some calculating!

Plasma volume in L = (Body weight in kg) x 0.05

Total blood volume in L = (Plasma Volume in L ) x (100/[100-hematocrit])

(That’s a little hard to read. So let me clarify. Take 100 minus the hematocrit. Divide 100 by the number that results from that operation. Then take the number you have now, and multiply it by the plasma volume in liters.)

And, here’s an example!

Our hero, Toughguy Manley, is a 70 kg man, with a hematocrit around 47. Let’s see how much blood he has.

So,

Plasma volume in L = 70 x 0.05 = 3.5 L

Total blood volume in L = 3.5L x (100/[100-47]) = 6.6 L

(Note: I’m using 47 because that’s the usual hematocrit for a man. If we were calculating a woman, I’d use 42.)

So, Toughguy Manley will have about 6.6 liters of blood in his body, or 6600 mL.

Now that you know how it’s done, you can plug in your own character’s weight in kilograms. (Here’s a handy calculator for people who use non-metric systems of measurement.)

I’ll wait while you do some calculations.

Excellent!

Now that we know how much blood your character has, we can figure out how much she can afford to lose.

The pretentious medical term for bleeding is “hemorrhage”. (“hemo-“ = blood, “-rrhea” = flow). The way doctors classify hemorrhage is by percentage of blood volume loss.

Here’s a quick rundown of the hemorrhage classes:

Class I Hemorrhage – Loss of up to 15% of blood volume. In a healthy character, this won’t cause too much trouble. At the very most, her heart will start beating slightly faster. But that’s about it. Her blood pressure won’t change appreciably, and she probably won’t have too many symptoms in general.

Class II Hemorrhage – Loss of 15-30% of blood volume. Your character’s heart will beat faster to circulate the remaining blood faster, to make up for the fact that there’s less of it. Her blood pressure will undergo a mild to moderate decrease, and she may start to have some symptoms related to the drop in blood pressure. For example, her skin will get cold and clammy as her peripheral blood vessels narrow down, squeezing the blood out of the skin so it can supply more vital organs. She may feel light-headed, and have some changes in her mental status. If she tries to sit or stand up quickly, she may get dizzy. She won’t make as much urine, since there’s less volume passing through her kidneys for processing.

Class III Hemorrhage – More than 30% blood volume loss. The symptoms that started to show up in Class II will get worse. Her heart will beat very quickly, but it won’t be enough to keep her blood pressure up. The blood pressure will fall even more dramatically, resulting in even less perfusion of the skin and the extremities (which will make them cold to the touch), and her mental status will decline significantly.

Class IV Hemorrhage – More than 40% blood volume loss. Your character’s body will not be able to compensate for a blood loss this severe. She must either get an emergency transfusion, or she will die from hemodynamic decompensation.

So with this information, now we can figure out how much blood, to the milliliter, will leave your character’s body during your dramatic wounding-and-possibly-killing-of-character scene!

Let’s have an entertaining example!

Remember, Toughguy Manley is a 70 kg male, and he has about 6600 mL of blood. He’s just found the Seekrit Hiding Bunkur that houses the Doomsday Device of Doom (Of! DOOOOOOOM!). Suddenly, during the dramatic climax of the story, he’s shot by Best Friend McTurncoat, who was actually working for the Evil Bad Dudes all along! Now, he can’t die from this, because he has to tell Gorgeous Genius just how badly he’s fallen for her, and he has to be just loopy enough that he’ll tell Gorgeous Genius just how badly he’s fallen for her! So, let’s put him at an early Class III hemorrhage. Say, 32% blood loss.

6600 mL x 0.32 = 2112 mL, or 2.1 L

Toughguy Manley has lost a bit more than 2 liters of blood. He’s giddy, his heart is beating like crazy, his blood pressure is low, and his hands and feet and skin are cold and clammy. And he’s still losing blood. And Best Friend McTurncoat is standing over him, expressions of triumph and deep anguish fighting for dominance on his face.

It’s not looking good for Toughguy Manley.

Luckily, at that moment, Gorgeous Genius activates the Doomsday Device of Doom (Of! DOOOOOOOM!), after re-jiggering it to use only a small percentage of its capacity, and to affect only Evil Bad Dudes! (Plus, now it writes novels! And assembles bicycles! And makes three kinds of french toast!) All the Evil Bad Dudes fall over unconscious, and the day is saved! Hip, hip, hooray!

And as Gorgeous Genius saves Toughguy Manley’s life using the blood-transfusion setting on the rejiggered Doomsday Device of Doom (Of! DOOOOOOOM!), he professes his undying love for her and for her absolute bad-assery. And for physiology. Because physiology rocks.

The End.

Hey! If you want me to answer a question about using medicine in fiction, shoot me an email! doctorgrasshopper (at) gmail (dot) com. (Remember, though, that I don’t have a lot of time to research answers, so please be patient with me. Thanks!)

Picture:

http://thistosay.blogspot.com/2009/07/firefly-out-of-gas.html

References:

Ganong, William F. Review of Medical Physiology. 21st edition. McGraw-Hill, 2003.

Manning, James E. Fluid and Blood Resuscitation. Tintalli’s Emergency Medicine, Chapter 31. McGraw-Hill, 2004.

The contents of this site, such as text, graphics, images, and other material contained on the Site (“Content”) are for informational purposes only. The Content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read on this Site!

If you think you may have a medical emergency, call your doctor or 911 immediately. This blog does not recommend or endorse any specific tests, physicians, products, procedures, opinions, or other information that may be mentioned on the Site. Reliance on any information provided by this blog, or other visitors to the Site is solely at your own risk.

The Site may contain health- or medical-related materials that are sexually explicit. If you find these materials offensive, you may not want to use our Site. The Site and the Content are provided on an “as is” basis.

If you use this as if it were real medical information, I will turn on my own Doomsday Device of Doom (Of! DOOOOOOOM!) (After it does my dishes, of course….)

Published in: on August 7, 2010 at 10:51 am  Comments (17)  
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Limp. (No, not what you’re thinking.)

Dear Dr. Grasshopper:

In my fantasy novel, I have a character who gets attacked by a cross between an orc and a werewolf. Well, he tries to stop an attack on someone else and gets his leg clawed. The outcome I want from this is for the character to have a permanent limp as a reminder of the day a myth appeared and sliced him up. Where would be a plausible place to be cut by three claws (and how deep) to cause such a limp?

To answer this question, I sought out the expertise of Rob, a fellow med student with a special interest in Physical Medicine and Rehabilitation (PM&R). Rob the great! Rob the wonderful! Rob the red-headed!

Everyone wave at Rob!

. . . . . . . . . . . . .

Seriously. Wave at him. He spent a good amount of time helping me out.

I don’t see you waving.

Fine. Be ungrateful. I’m sure he understands. He’s just nice like that.

At least I appreciate him.

Anyway.

With his help, I give you:

A limp rundown!

Seriously. Quit giggling.

(Note: There are a lot of different types of limps. This post will concentrate on the ones that might result from getting clawed in the leg by a cross between an orc and a werewolf. There are others that I’m not going to touch on, but you can see a listing of more types here)

“Limp” is a layman’s term to describe a disturbance in a person’s gait, or normal pattern of walking.

How do limps develop?

Initially, the change in your character’s gait would be caused by inflammation at the site of injury. It hurts, so he doesn’t do what he would normally do walking-wise.

However, that alone won’t cause a permanent limp. Unless there’s constant inflammation, like from a localized but persistent infection.

To get a permanent limp, you’ll need one of three things:

-Constant pain (for example, from constant inflammation)

-Structural damage to muscles and/or tendons

-Nerve damage

Immediately after the initial injury, your character would most likely have an “antalgic gait”. (ant = against or opposed to, algia = pain)

His gait would minimize the time spent on the injured side. The woman in this video walks with an antalgic gait. Which side is the painful one?

After the injury had healed, the gait disturbance pattern would be dependent on where the injury occurred.

If the muscles of the hip girdle are injured, your character will walk with a “trendelenburg gait”. (Tren = … Just kidding; it’s a person’s name.)

The hip girdle drops on the injured side with the trunk sort of swaying over it to maintain balance.

This video is a little over-exaggerated, but it’ll give you the general idea.

Pain or stiffness in a joint like the knee can cause a “circumduction gait”. (Circum = around, duct = lead, bring, take in) (This pattern is also known as a hemiplegic gait. (hemi = half, plegia = paralysis) )

This could come from the development of scar tissue around a joint. Basically, it prevents the leg from bending properly during the gait cycle. The character would walk with a straight leg.

Get up and try to walk with a stiff, straight leg.

I’ll wait.

Notice that it’s easier to move the leg forward by swinging your foot in a semi-circle, first away from your body and forward, then back to midline. You can see that happening in this video, which is entertainingly old-school:

Damage to the peroneal or tibialis anterior nerves would give your character a “foot-drop gait”, also known as a “steppage” or “equinus” gait.

If the character’s peroneal or tibialis anterior nerves are damaged, the muscles that keep his foot in a 90-degree orientation will not work. So basically, his toes will drop down to the floor every time he lifts his leg. He will compensate for this by lifting his leg higher, so he doesn’t trip over his own toes.

If he wants to hide his limp, he could wear a shoe or a boot that holds his foot firmly in the proper 90-degree orientation.

The thing about nerves is that they are capable of growing back (very, very slowly) to bridge clean cuts such as the one that might be caused by an orc/werewolf hybrid’s claw injury. However, the nerve could also be compressed by the development of scar tissue, and that would make it much less likely that the nerve would be able to regain its usual function.

So, which should you use, dear reader?

Rob thinks you should go with a circumduction gait, perhaps via a claw injury to the knee itself or surrounding structures. Your character could develop extensive scar tissue, which would hold it stiff and rigid.

But, there alternatives if you don’t like Rob’s idea. And you want to make him cry. Especially since you also didn’t wave at him earlier.

Your character could also get a foot-drop / steppage gait from scar tissue compressing the peroneal or tibialis anterior nerves in the lower leg.

If you want a trendelenburg gait, he should be clawed deeply over the hip girdle area.

If you want an antalgic gait, consider giving him a persistent, low-grade infection as a source of ongoing inflammation. But that would change a lot with time, and may be life-threatening as well. I’d suggest that it doesn’t fit your scenario quite as well.

Hope that helps! Rob and I both thank you for writing!

(Even if you didn’t wave. )

Pictures:

The contents of this site, such as text, graphics, images, and other material contained on the Site (“Content”) are for informational purposes only. The Content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read on this Site

If you think you may have a medical emergency, call your doctor or 911 immediately. This blog does not recommend or endorse any specific tests, physicians, products, procedures, opinions, or other information that may be mentioned on the Site. Reliance on any information provided by this blog, or other visitors to the Site is solely at your own risk.

The Site may contain health- or medical-related materials that are sexually explicit. If you find these materials offensive, you may not want to use our Site. The Site and the Content are provided on an “as is” basis.

If you use this as if it were real medical information, I’ll sic Rob on you. Don’t laugh. He’s wonderful, great, and red-headed. . . but he’ll totally take you down. You have been warned.

Published in: on April 8, 2010 at 10:43 am  Comments (2)  
Tags: , , , ,

Superballs, Pockets, and Fun With Awesome Molecules

Dear Dr. Grasshopper,

I’m writing a military sci-fi novel, and I’ve run into a medical snag.

I know (or like to think) that there are certain toxins which can rob the blood’s ability to transport oxygen. Would you happen to know what the emergency treatment is for such a situation, or could you point me in the right direction?

Yeah, man!

You’ve basically described a classic case of carbon monoxide poisoning. Which was one of my favorite topics early in med school. (I even used it as a plot point in a novel I started writing. . . and then trunked because it had no plot.)

How does your blood carry oxygen?

The red color of your blood is from all of the red blood cells floating in it.

Red blood cells are really just sacks full of four-unit proteins called hemoglobin. This a representation of a hemoglobin protein:

Each of the parts of the protein has a little “pocket” that contains a unit of heme. I think heme is a truly awesome molecule, so I’m going to show its structure below. Notice the “Fe” in the middle. That’s the symbol for iron, and it’s very important to heme’s function. The other letters are also symbols for atoms; this tells you what the molecule is made of. C = Carbon, O = Oxygen, H = Hydrogen, N = Nitrogen.

Just look at it for a sec. Isn’t it gorgeous?

Quit geeking out, Doc.

Must I?

Yes. Get on with it.

Fine. Back to the point.

Heme has a good affinity for oxygen for the purposes of oxygen transport: It binds oxygen tightly enough to carry it around, but loosely enough to let it go when it arrives at its proper destination. (This “oxygen + hemoglobin” combination is called “oxyhemoglobin”.)

Enter carbon monoxide. Carbon monoxide is made up of one carbon atom and one oxygen atom. (The name tells you that, if you break it down.) Carbon monoxide also likes to bind to heme, in the same spot where oxygen likes to bind, right in the “pocket”.

Problem is, it binds WAY TOO TIGHTLY to the pocket, and is very difficult to release. (This “carbon monoxide + hemoglobin” combination is called “carboxyhemoglobin”. See, medical terminology isn’t THAT scary, is it?)

Carbon monoxide can not be used in the same way as oxygen. And it takes up all the heme groups that should be used to transport oxygen. And it doesn’t like to let go of heme once it’s grabbed on.

Long story short: Carbon monoxide interferes with proper oxygen transport, which seems to be the scenario you’ve described.

Fun with chemistry! Competition

Bear with me; we’re going conceptual. But I promise, it’s relevant to the subject matter.

First, picture a tank with a bunch of superballs bouncing around in it. That’s what goes on at a molecular level in most substances. A bunch of molecules bounce around, colliding with each other at random.

Now picture these superballs with extra appendages or depressions, three-dimensional fittings like puzzle pieces. If two balls hit each other in exactly the right orientation, they’ll attach together. The pairs, once formed, can also break apart spontaneously.

That’s how molecular events occur. And for these purposes, let’s say that these events are pretty common.

Now.

You have a population of red superballs with a particularly-shaped depression in them; they can only admit a certain shape of superball appendage upon collision. Now, two populations of superballs have that particular shape of appendage, one green population and one yellow population.

They can both attach to the red balls, but once they’re attached, the yellow balls don’t let go quite as easily as the green ones do. So, if you have equal populations of the two, eventually you’ll end up with more yellow-red pairs than green-red pairs. The yellow out-competes the green for attachment sites.

The only way you’ll get more green-red pairs than yellow-red pairs is by making sure the population of green balls FAR outnumbers the population of yellow balls.

Treating carbon monoxide poisoning, using molecular competition

This basically explains the basis of treatment for carbon monoxide poisoning. The red balls are the hemoglobin, with its particularly-shaped pocket. The green balls are oxygen, that can attach with some affinity. The yellow balls are carbon monoxide, which have a much higher affinity for the hemoglobin.

So, if you have a bunch of carbon monoxide bouncing around the system, oxygen will be out-competed for binding sites in the pockets of the available hemoglobin. The only way to correct this is by increasing the population of oxygen molecules as far as you can; putting in something like ten green balls for every one yellow one. Eventually your population will consist of mainly green-red pairs (oxyhemoglobin) and very few yellow-red pairs (carboxyhemoglobin).

So, the treatment for carbon monoxide poisoning is basically, saturate a person with oxygen in order to outcompete the carbon monoxide.

In answer to your question:

You can use carbon monoxide for your scenario if you want to; it seems to fit well. At that point you’d just turn up the oxygen on the bridge or find your character an oxygen mask, and out-compete the carbon monoxide.

Alternatively, you can propose another toxin that interferes somehow with the hemoglobin molecule, and then make up an antidote that (a) displaces the toxin from its site of interference or (b) binds up the toxin to keep it from getting to the site of interference.

Hope that helps! Thanks for writing!

Pictures:

The contents of this site, such as text, graphics, images, and other material contained on the Site (“Content”) are for informational purposes only. The Content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read on this Site!

If you think you may have a medical emergency, call your doctor or 911 immediately. This blog does not recommend or endorse any specific tests, physicians, products, procedures, opinions, or other information that may be mentioned on the Site. Reliance on any information provided by this blog, or other visitors to the Site is solely at your own risk.

The Site may contain health- or medical-related materials that are sexually explicit. If you find these materials offensive, you may not want to use our Site. The Site and the Content are provided on an “as is” basis.

If you use this as if it were real medical information, I’ll fill all of your pockets with superballs. They will become very bouncy pockets.

Published in: on February 6, 2010 at 11:59 am  Comments (7)  
Tags: , , , , , ,
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