LOC, syncope, or passing out can have many causes but they all share the same result--low blood pressure to the brain. The brain needs oxygen and glucose to function, and both are carried there by blood. The cardiovascular system is constantly working to ensure that the brain gets what it needs, using a pump (the heart), some pipes (the blood vessels), and something to pump through the pipes (blood).
To maintain that blood pressure and the supply of glucose and oxygen to the brain, the body can:
- increase cardiac output; the heart can work harder
- increase vascular pressure; the arteries can constrict
- the kidneys can try to keep the fluid levels up
- breathing can become deeper and faster
- the liver and muscles can release stored glucose or manufacture new glucose
Here's how things can go wrong.
FLUID PROBLEMS--hypovolemia--fancy word for saying that there's not enough fluid in the pipes. No matter how hard the pump works, if there's not enough fluid, the brain won't get its energy. That fluid is of course blood, and for situations that could arise on a trail there are only really two causes of hypovolemia; dehydration and blood loss.
Dehydration is preventable--just pay attention to your fluid intake. No, you don't want to just drink pure water if you are sweating a lot because you'll be losing electrolytes. Electrolyte loss may or may not cause cramping first, but if it's a hot day and you're feeling lightheaded or dizzy when standing up, there's a good chance it's related to dehydration. This is hard to *fix* in the woods, but easy to prevent. Drink up. If the dehydration isn't too bad, some recovery can happen while lying down flat--or with the legs elevated. The kidneys will be working to hold on to fluid as best they can, but you've got to fill the tank.
The other cause of hypovolemia, blood loss, is also hard (like really, really hard) for *fix* on a trail, but the key point here is that major bleeding needs to be controlled; whether that's just bandages and compression, packing a wound, or a tourniquet. If bleeding is internal (from major trauma, like a broken femur or significant injuries to the torso), the person needs to get out ASAP.
PUMP PROBLEMS--the pump, as mentioned, is the heart, and if the heart isn't working that's not good. Some people can pass out from a transient cardiac problem, such as a brief abnormal heart rhythm, but some other problems may not be so brief, and if the heart just stops, that's cardiac arrest. The treatment for cardiac arrest; cardiogenic shock is CPR--cardiopulmonary resuscitation and an AED automatic external defibrillator (which is unlikely to be with someone on a trail). If someone passes out and one of these other causes doesn't seem likely, further testing may be needed.
PIPE PROBLEMS--the diameter of the pipes, blood vessels, is an important factor in maintaining blood pressure. Narrow, constricted vessels increase blood pressure, and wider, dilated vessels decrease blood pressure. Many blood pressure medications act in different ways to help decrease vessel constriction, but for trailside issues, the big three will be anaphylaxis, neurogenic shock, and vasovagal episodes.
In the woods, I'd guess that the most likely cause of anaphylaxis would be a bee sting, but I supposed it's also possible for someone to have a bad peanut allergy and someone else to whip out a PB&J sandwich. In anaphylaxis, the blood vessels dilate significantly, resulting in a major drop in blood pressure. Allergy medications, specifically antihistamines (benadryl, diphenhydramine, cetirizine, zyrtec, allegra, fexofenadine, claritin, desloratidine, etc) really don't do anything in true anaphylaxis--the only treatment is epinephrine. Use of an epipen is an automatic call to 911, One epipen might do the trick, might not.
Another possible cause of low pressure related to the pipes--blood vessels--would be neurogenic shock. This isn't great and would be the marker of a severe spinal cord injury. The brain sends signals to the blood vessels and heart via several mechanisms, but if the spinal cord can't transmit those messages, the the vessels will dilate and the heart will slow down. Not much to say about this... neurogenic shock is going to be from significant trauma. With trauma this bad, you're looking at calling for help no matter what. To differentiate between traumatic internal blood loss as a cause of low blood pressure or neurogenic shock, you'd expect to see additional neurologic symptoms (weakness, loss of sensation) with a spinal cord injury. Also, low blood pressure from blood loss would need some time to show up, and would likely combined with a rapid heart rate.
And finally, one other possible cause of passing from low blood pressure is a vasovagal episode. Of all of these that we've discussed so far, this is the least concerning. Your body can have a temporary drop in heart rate and blood pressure from extreme fear, anxiety, or phobias--like seeing blood, seeing a snake or seeing a spider. The person will likely have a couple of seconds of warning--feeling nausea or tunnel vision--and if he/she sits down, the episode can be aborted. While everything else mentioned above will need some intervention (from drinking fluids to starting CPR), with a vasovagal episode, you're likely okay to keep on doing what you're doing.
The last two to review are low blood glucose and low oxygen.
With low blood glucose, this is another issue that easy to prevent but hard to fix if it goes too far--you can't give an energy bar or something to someone who is unconscious. A person will likely feel symptoms before getting to the point of passing out if glucose is getting low, and those symptoms are going to be remarkably similar to those with dehydration--feeling shaky, lightheaded, and dizzy. So if you or someone is feeling that way when you're out on the trail, taking in some fluids with glucose and electrolyte is the best option.
I'm going to save low oxygen situations for another post, because I can't think of any causes that are likely to be encountered on the trail (except anaphylaxis, which can block the airway).
So let's recap:
- Riding, hiking, running and feeling weak, lightheaded, and shaky--take in fluids, electrolytes and glucose so that YOU ARE NOT THE ONE WHO PASSES OUT, and make sure those that you're with are keeping up with this as well.
- Someone passes out--immediately take note of the situation and check for a pulse. If no pulse, CPR is needed.
- If there's a pulse--likely fast and thready (weak), get back to considering the situation:
- Pass out after bee sting--pass out--anaphylaxis--needs EpiPen
- Pass out on a hot day or long effort--not drinking enough and/or not enough glucose--dizzy, lightheaded--dehydration/hypoglycemia--watch for early signs--prevention is key
- Major fall or crash with lots of blood--Stop The Bleed--blood loss will lead to unconsciousness
- Major fall or crash--no visible blood, but significant injury to torso--suspect internal bleeding--get help ASAP
- Pass out after major fall or crash--no visible blood but suspected spinal cord injury--damage is done--but needs help ASAP to prevent further damage, may not have pulse and will need CPR as above
- Saw blood or spider or snake or encountered other phobia--recovery should be quick
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