BAM! You’re On The Floor!

(Well, I could do without the obnoxious laugh track. Things like this were so much funnier to me before I started with the whole medical training thing. Now all I can think about is how much their medical bills are going to be.)

(Anyway. Article.)

We see fainting everywhere in fiction, from swooning damsels in distress to buffoons scraping for cheap laughs in mindless comedies. And heroes are always fighting off a loss of consciousness when they’re being tortured by evil bad dudes everywhere, and annoying sidekicks are always dropping into the nearest pile of horse puckey at the sight of blood.

So what’s going on? Is there a medical explanation?

Of course! 😀

If your brain doesn’t get enough blood flow, it’ll shut down. And this causes a person to lose consciousness. That’s called syncope. If they’re upright, they’ll fall down. (If they don’t lose consciousness, but still experience dizziness and other near-syncope-like symptoms, it’s called….near-syncope. Thought it was going to be more dramatic, didn’t you? 😀 ) True syncope is also characterized by a relatively quick recovery, with no real neurological after-effects.

So, listen. Gravity is always pulling your blood down toward the center of the earth. Your cardiovascular system is all set up to fight against this force to keep the blood circulating adequately to all parts of your body, no matter what orientation it’s in. It’s a rockin’ system.

But if something goes wrong with the cardiovascular compensation against gravity, gravity wins. And the blood gets pulled away from whatever is the highest part of the body. If it’s your brain, your brain will shut down until enough blood gets back into it.

As a side note: fainting sure isn’t fun, but it’s a pretty smart failsafe in case gravity starts winning. It gets you horizontal, on the ground, so your brain is a low enough point that gravity won’t pull too much blood away from it. Cool, huh?

So what causes the failure in the first place?

There are a lot of reasons why people faint. As a matter of fact, I dreaded getting a syncope case during my time-limited practical exam for my boards, because there was SO MUCH WORKUP to do that I’d never get to everything in time. The ultimate cause could be in the heart, or the brain, or the lungs, or an imbalance in the blood…..and it could be any number of causes within those categories. Like I said, lots of reasons.

But how about fainting in fiction? The guy who passes out instead of revealing the secret location of his hidden army while under duress? The girl who can’t stand the sight of needles? The dude that gets overrun by carnivorous spiders because his maladaptive phobia causes him to faint when he should be running away, and thus provides an opportunity for us to see exactly what said carnivorous spiders would do to our erstwhile hero if they could manage to outsmart her? The poor folks in the wedding videos?

It’s probably all from the same end cause: vasovagal syncope.

Say what now?

Vasovagal (vaso – blood vessels, vagal – having to do with the vagal nerve and parasympathetic function) syncope (fainting).

This can happen with a strong emotional shock, or with a large, sudden amount of pain.

Here’s what happens. The sympathetic and parasympathetic influences are in their tug-of-war balance, keeping heart rate, blood pressure, breathing rate, etc. all around their preferred normal baseline ranges. Suddenly, there’s pain or terror, or something that strongly stimulates the sympathetic branch of the nervous system (the fight-or-flight branch)! The sympathetic tone leaps WAY out of balance, and the tug-of-war leans STRONGLY to the fight-or-flight side.

In reaction to the increased sympathetic tone, the heart contracts HARD! (Remember, in a fight-or-flight situation, it’s a good idea to have more blood pumping through your system.)

Then, sensors in the heart that are supposed to be keeping an eye on the balance between the sympathetic and parasympathetic tone see that the sympathetic tone has completely overwhelmed the parasympathetic tone! And they freak out! They have to balance the discrepancy somehow! So they send signals to increase the parasympathetic (“vagal”) tone!

But then, the overwhelming sympathetic tone reduces to a certain extent, because it was probably a bit of an over-reaction.

Now, all you’re left with is an overwhelming parasympathetic influence, which drags things STRONGLY over to the rest-and-digest side! This means heart rate, blood pressure, etc. all drop like stones. And if your blood pressure drops enough that it can’t pump enough blood to your brain, BAM! Your brain shuts down and you’re on the floor.

Illustrate that point with a random side story!

How funny that you’d encourage me to do such a thing. It’s almost as if we were both internet-based entities being written by a single author for the purpose of increasing the accessibility of a blog post!

I’ve actually experienced vasovagal syncope. Pretty recently, as a matter of fact. In my hapkido class, I was teaching a lower belt how to do a particular combination of a joint lock and throw. And she did it really well. So well, in fact, that she threw me right off the mat. I hit my knee really hard on the floor, and it hurt like crazy.

And then, not realizing that I had just experienced a potentially triggering stimulus, I got up off the floor to show her how to position herself so she didn’t throw me off the mat the next time.

And I started feeling nauseous. And dizzy. And woozy. And a little hot. And what do you know? I actually recognized the symptoms! I felt my pulse, and sure enough, it was much slower than it should have been under the circumstances. And I remember thinking, “If I don’t lie down on the floor RIGHT NOW, I’m going to fall down on the floor.” So I lay down. Just in time.

Every time I tried to sit up, I felt the same faintness. So I stayed down until my body figured out that I was actually okay, and my autonomic nervous system sorted itself back out into its proper balance.

Okay, but this whole explanation doesn’t exactly follow for the wedding videos. I mean, the brides weren’t THAT hideous. Neither were the grooms, for that matter.

Well, there’s something else that causes a vasovagal response.



If there’s nothing going on that activates your sympathetic system, your autonomic nervous system gets so bored that the sympathetics just shut down. Your heart rate falls. Your blood pressure falls. You lose tone in your blood vessels, and they dilate to their full extent. Blood falls down through your legs and away from your brain. And bam! You’re on the floor!

This happens to medical students all the time. (A medical student’s job during a surgery is usually to stand and watch. And hold the retractors that pull tissue away from where the surgeon is working. For. Hours. On. End.) One of the first things they told me during my surgery rotation was what to do if I started feeling faint. Because situations like that are very, VERY risky for the whole vasovagal syncope thing.

It also happened to my little brother a lot when we were singing in choir performances under hot lights, doing weird musical-but-non-physiological things with our breathing. It happens to people who are standing in crowds listening to politicians talk. It happens to people standing during a wedding ceremony.

But this all hinges on gravity, right? What about astronauts?

Okay, I gotta drop this in here. I actually don’t know too much about what happens in an actual zero G environment. I can guess. But, I think it’s even more interesting what happens after they get back to Earth.

After a while in zero G, astronauts’ bodies tend to forget their antigravity compensation mechanisms, because the body hasn’t used them for a while. So when they get back into a gravitational environment, they experience orthostatic hypotension for a while until the compensatory mechanisms remember how to kick back in.

Oh, how I loves me some physiology! (Does it show?)

(Anyone else wanna clock that guy at the end, or is it just me?)


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

McDermott, Daniel, et al. Approach to the adult patient with syncope in the emergency department. UpToDate, May 2010.

Sabatine, Marc S. Pocket Medicine, 3rd edition. Lippincott Williams & Wilkins, 2008

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 gravity on you. Yeah, that’s right. Gravity! What now, mutha-luvah?

Published in: on August 26, 2010 at 10:47 am  Comments (22)  
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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.


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.


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!)



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 (18)  
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Stories From Med School: Hyperthermia

As a fourth-year medical student, you’re supposed to know enough about what’s going on in a patient’s treatment to be able to follow along with the rest of your team, and even to contribute a few aspects to the patient’s care. As a result, a fourth-year student at my med school is often distinguished from a third-year student by the title of “Sub-Intern”, or “Sub-I”.

I did my Sub-I in internal medicine at the county hospital, and then I requested a rotation in Intensive Care in the same hospital, with one of the toughest old-guard docs the hospital had. I figured I’d learn a lot. And I did.

Anyway, this story is from my ICU month.


One Tuesday at four in the morning, when I was on call with my team, a patient came onto our service in really, really bad shape. He was a young guy (younger than me, which still gives me a touch of existential crisis when it happens), in his teens.

He had been running away from the cops with a stash of cocaine, about eight ounces in a plastic bag. He realized that he was going to get caught, so he decided to get rid of the evidence.

By swallowing it.

And eight ounces of cocaine entered his system. He was unconscious within minutes.

Here’s what cocaine does to you. It cranks up the thermostat in every system in your body. Your heart rate goes through the roof (which is why you can get heart attacks from cocaine use), your blood pressure goes through the roof, your breathing ramps up, et cetera. Your temperature also skyrockets.

When we assessed our friend, his temperature had reached 106 degrees. That’s well into brain-damage territory. If we didn’t bring his temperature down, and fast, he’d die. And if he didn’t die, he’d likely come out of this in a permanent coma.

I’ve never seen my team move so fast.

So, we started an IV of refrigerated saline, and set the drips as fast as they would go. We packed him in ice, and covered him with a cooling blanket that would draw even more heat from him.

If you need to cool someone down, the best places to put the cooling sources are in superficial (close to the skin) areas with high blood flow. In practical terms, that means neck, armpits, and groin.

But that apparently wasn’t even enough. The cocaine was still raging through his system, telling it to RAMP UP! RAMP UP! RAMP UP!

We had to bring his temperature down even faster , and it had to happen SOON! The only other thing we could do was to blow cool air on him in addition to the other measures.

Which meant we needed a floor fan. And as the junior member of the team, it was up to me to obtain one.

In retrospect, the team might have just needed me out of the way; the fan wouldn’t help THAT much. But I didn’t realize it at the time. At the time, it seemed like the most important task in the UNIVERSE!


Let me tell you something about the county hospital. It’s a huge old building with maybe ten floor fans in total. They are all located at the nursing stations.

In August in that part of the country, floor fans become a desperately sought-after commodity, and are fiercely guarded by the nurses. Understandably. That hospital is not the friendliest working environment, temperature-wise, and nurses spend their entire day running around.

But if you need a floor fan in August…especially if you’re a medical student…you need to either run across a really, really understanding nurse…or you need to risk pissing one off.

I did not have time to find a really, really understanding nurse. There was a kid dying in the ICU. And a floor fan would help.

Cue Mission: Impossible music.

I ran through each ward on each floor of the hospital at top speed, taking stairs between floors two at a time. Patients and nurses eyed me curiously as I flew past. A doctor running in a hospital usually means an emergency. But a med student running at four in the morning? Who knew what that meant!

Finally, I located a precious fan on the fourth floor, cooling off the momentarily empty 4 East nursing station.

I then called an elevator.

And made a mad dash.

Three things happened at once.

1) I unplugged the fan and hefted it against my shoulder.
2) The night nurse appeared from a patient’s room.
3) The elevator dinged down the hall.

We both started to run. And we both started to yell.

“Where are you taking that! Come back here! What are you doing?” She didn’t know why I was taking the fan. She just knew that the nursing station would be practically unliveable for the rest of the night without it. Like I said, who can blame her?

“I’m the Sub-I on the ICU team!” Oh, there was no way I was stopping! Patient care trumps nursing comfort, and Sub-I safety! “My pager number is 123-4567! This is for a patient! I’ll bring it back! I promise!”

The elevator doors started to close. The night nurse was right behind me.

I dashed in, just in time for the doors to close behind me and right before the nurse could catch the elevator. I punched the button for the ICU floor so the nurse would not be able to call back the elevator.

I’d made it.

I ran back to the ICU as fast as I could, and we set up the fan. And we worked. And we worked.


The kid was in the ICU until the end of my rotation. On the last day of the rotation, he woke up a bit.

“Hello,” we said.

“Hello,” he carefully said back.

“How are you?”


Success! We had saved enough of his brain function that he had at least retained enough processing power for a simple conversation! We grinned at each other like idiots.

I left the ICU service the next day, so I have no idea how much function he recovered. But he survived to see his family again. So I call that a win.

And the floor fan was there, helping him stay cool, until I left the service.


On the last day, I took the fan back up to the nurses’ station on 4 East, and plugged it back in.

The nurses all exchanged looks. They knew who I was. And I was all alone, the baby gazelle on the Serengeti of the county hospital wards.

And I slunk out of there as fast as I could.


Bonus round! Which branch of the autonomic nervous system predominated in every single person in that story? Especially the teen?

Sympathy. And…parasympathy?

Ever wonder how our body knows how to do things and when to do them? There’s an incredibly complex signaling system in our bodies, working ALL THE TIME, without us having to do anything about it. Isn’t that cool?


Before you answer, I should inform you. It’s cool. It’s really cool.

If you say so.

I do.

Today I want to talk about the autonomic nervous system. “Autonomic” can be broken down into the roots auto = self, and nomos = arrangement or law. So, it’s the branch of the nervous system that is responsible for self-regulation. And when we’re talking about self-regulation, we’re talking about regulation of all kinds of bodily functions: from how quickly you breathe, to how much you salivate, to how big the pupils of your eyes are.

The autonomic nervous system is divided into two opposing forces: the sympathetic influence, and the parasympathetic influence. Both forces are acting upon every bodily system at all times. It’s like playing tug-of-war between two evenly-matched sides. There’s a balance point between the two opposing forces, and a dynamic system that keeps the balance point in place.

You can see an example of this kind of dynamic equilibrium in the first 25 seconds of this video:

So, what do the sympathetic and parasympathetic systems actually do?

I’ll break it down for you.

The sympathetic system is the “fight or flight” system. I like to remember it as, “everything you want to be doing while you’re running away from a lion.”

(well….hopefully more successfully…..)

So, what would be helpful when you’re running away from a lion?

You want your muscles to work really, really well. So you’re going to make sure they get a really good oxygen supply. You’ll dilate your muscular blood vessels, and your heart will beat faster and stronger to make sure enough oxygen is getting to your muscle cells. You’ll also breathe harder and deeper, making sure you have a lot of oxygen in your blood for maximum delivery.

What else? Well, you’ll want to see really well while you’re running away. So your pupils will dilate to a bigger size to let more light in.

And you’ll also want to inhibit a couple of parasympathetic functions, which… well, you’ll see why in a minute.

The parasympathetic system is responsible for the “rest and digest” functions.

Basically, it’s “everything that your body needs to do…unless you’re running away from a lion!”

The parasympathetic system lowers your heart rate and blood pressure. It slows down your breathing. It constricts your pupils and narrows your blood vessels to direct blood flow from your muscles to other important organ systems. It lets your eyes make tears.

The parasympathetic system increases salivation, which helps in the digestion process. It also increases the movement of the digestive tract, allowing you to digest food and excrete waste.

(Helpful tip: Avoid excreting waste while running away from a lion.)

Usually, these systems find an equilibrium point and stick with it, dynamically pulling against each other to maintain it. And they also react to stimuli, changing the equilibrium point as necessary to adapt to daily needs.

Let’s talk about heart rate as an example. A normal heart will contract about 60-100 times per minute. This represents the physiological balance between the sympathetic and parasympathetic influences. At rest, (such as when you’re sleeping), the influence of the parasympathetic function will increase, and your heart rate will slow. When you’re exercising, the influence of the sympathetic function will increase, and your heart rate will speed up.

Another example: your eyes aren’t completely dilated or completely constricted at any one time; they usually hang out around a particular size (that changes slightly according to age). They use the sympathetic and parasympathetic systems to adapt the diameter of the pupil to the amount of light the eye is receiving.

Then, when the particular condition that’s pulling the system in one direction (say, toward the sympathetic side of things) disappears, the other system (the parasympathetic side, in this case) will exert enough influence to bring the systems back into their favorite physiological set point.

How is that not cool?

Your operational definitions are problematic.

It’s still not cool enough? Fine. I hear sex sells.

Fun with autonomics!

The sympathetic and parasympathetic systems are both involved in sexual activity. The parasympathetic system is responsible for arousal, and the sympathetic system takes care of things such as male ejaculation. The mnemonic to remember which does which? “Point and Shoot”. See, doctors are funny!

“Funny”… “Cool”… “Fun”…. You see, this is what I’m talking about. I’m getting you a dictionary for your birthday.

::Sigh:: Another one?

The other ones clearly haven’t helped.

Okay, fine. It’s not cool and doctors aren’t funny. But I still think it’s pretty awesome. So there.

Oh, Dr. G. We really need to get you a life.

It’s going to have to wait till after residency.

Published in: on July 20, 2010 at 1:48 am  Comments (21)  
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