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Hypothermia - Cold Injuries timberlinetrails.net
(Information from the NWS)
Temperature (Degrees Farenheight)
Hypothermia in the mountains, as well as in many other outdoor locations (and even in cold homes of the elderly), is a very real
danger. Most people think of hypothermic dangers when temperatures are below freezing, but in reality, most cases occur when
temperatures are well above freezing. The reason for this is anybody's guess, but it could be that people take below freezing
temperatures much more serious, and properly prepare for them. But hypothermia can set in under any condition where the body
is losing more heat than it is generating. The elderly are particularly susceptible to this, and I have known older folks who have
complained about the cold when temperatures were in the 80's (degrees F) and even higher. So obviously there is a lot going on
when it comes to the body's ability to fight off cold.
The human body strives to maintain a temperature at a steady 98.6 degrees F. Anything below this begins to cause stress on the
system. Mild hypothermia would set in with a body core temperature between normal and 96F. Moderate would be 92-96F, and
severe would be 86-92F. Below 86 degrees F, death is likely.
The body's priority is keeping internal organs at that ideal
operating temperature (98.6F). Proper operating temperature
is critical, because our body is a chemical factory, and all the
reactions that take place must happen under precise
conditions. Above 105 F many body enzymes become
denatured and chemical reactions cannot take place Below
98.6 F chemical reactions slow down or even cease. When
the body cannot function chemically, death comes quickly.
This is particularly true when it comes to vital organs such
as the heart, lungs, brain, etc. This is why the body when
faced with heat loss, will begin to shut down blood flow to
the extremities such as the hands, arms, feet, legs, nose,
ears, etc. It does this so that precious heat will be preserved
for the vital organs to maintain life.
Now to understand what we need to be aware of when it comes to preventing hypothermia in the mountains, or anywhere else for
that matter, is an understanding of how the body loses heat. With this understanding, we can then take preventative measures. The
different forms of heat loss are as follows:
This type of heat loss has to do with the movement of molecules across the surface of your body parts. It works this way. When
the temperature gradient as explained above is below the 98.6 degrees, your body will loose heat to it's surroundings, because the air
molecules that come in contact with your skin absorb heat from your body. Now when these air molecules are moving at a faster
rate, such as in windy conditions, your body is constantly being bombarded by newly arriving cold molecules that suck away heat at
an alarming rate. This is true not only of moving air, but of any moving substance coming in contact with your skin. Moving water
would be a good example of another substance that when is motion can cause a greater heat loss.
This is what windchill is all about. Cold coupled with a wind is always more serious when it comes to hypothermia. The below chart
demonstrates this when it comes to the danger of frostbite.
The image to the left is a photo of a few of the toes on my right foot after incurring Frostbite
on Split Mountain in the Sierra Nevada. This was a result of a forced bivouac at approximately
13,000 feet (see photo at top of this page). We will discuss frostbite latter on.
How to avoid heat loss due to convection:
1) Take shelter from the wind (get into your tent or bivy bag, or get under a rock or into some
other form of natural shelter)
2) Put on a good windbreaker (with hood) in order to stop the movement of air across the
body. Wind pants should also be used when you are in cold and windy conditions.
Heat is required or lost anytime a substance changes state (solid to liquid, liquid
to gas, etc) For evaporation to take place, heat is required to change a liquid to a
gas. This is why the body uses the mechanism of sweat to cool the body. When
the liquid sweat from the body comes in contact with moving air, evaporation
takes place, which draws heat from the body to facilitate the change in state from
liquid to gas. While this works perfectly well during hot or warm conditions,
evaporation is not a good thing when hypothermia is a danger.
Further loss of heat in cold conditions from evaporation is common when the
following occurs. A hiker is working hard going up a slope and begins to sweat
because the body is burning a lot of fuel and needs to remove some of that extra
heat. The hiker then stops to rest a bit, and the moving ambient air then comes in
contact with the sweaty hiker. Evaporation then takes place. The hiker feels an
immediate chill. This is the most common form of evaporative danger when it
comes to hypothermia for the climber and/or hiker, etc.
How to lesson the dangers of cold from evaporation:
1) Proper attention to clothing is critical here. You do not want to get soaked
This is the simplest form of heat loss to understand. It is the
loss of heat to the environment due to the temperature
gradient between the body and whatever is contact with it. It
is the temperature difference between the body (98.6 degrees
F) and the surrounding environment. If the current outdoor
temperature for instance is 58.6 degrees, then we have a 40
degree temperature gradient or differential (98.6 degrees F
minus 58.6 degrees F).
Conduction is the most serious type of heat loss because it is
so rapid when compared to the others types of heat loss. It
has to do with the warmth lost from direct contact with an
object. A particularly severe type of conductive heat loss
occurs when the body comes into contact with a cold solid or
This is why falling into a stream or lake is so deadly during
times of very cold weather.
How to reduce heat loss due to conduction:
1) Immediately replace any wet clothing with dry clothing, and
dry any wet areas of the body off as best as possible.
2) Do not risk falling into any water. Falling into water under
cold conditions could be a death sentence if you are unable to
dry off and replace the wet clothing immediately.
3) Always use a thermo-rest, a foam cell, or some other
insulating type material between you and your sleeping bag. If
conditions are cold, I also take out my foam pad to sit on, or lie
on when taking an extended break or around camp.
CONCLUSION ON HEAT LOSS:
Preventing heat loss is the best way to avoid hypothermia. If you let things get out
of hand, it will be far more difficult to reverse the potential damage done to the body
due to heat loss, then to prevent it in the first place. So to boil it all down, it comes
down to a few simple things.
- Proper clothing is crucial. If you have a good layering system, along with a
good water proof, windproof, and breathable shell (like Gortex@) you will
greatly reduce or eliminate the danger of heat loss from Convection,
Evaporation, and (to a much lesser extent), Radiation. This means playing it
smart, and being alert to what your body is telling you. You may deceive
yourself, but your body doesn't lie. Take heed, and reduce layering when you
start to sweat, and add layering when you start to get cold.
- Stay dry. Heat loss from Conduction in water is deadly, because it is so rapid.
Remove wet clothing immediately. Getting soaked with sweat when it is cold is
usually a sign that you are not playing it smart when it comes to heat
regulation. It's one thing to have the layer next to your skin get wet (this is almost
unavoidable if you are working hard climbing or hiking. This layer should not be cotton, but
something like smartwool@ that provides warmth even when wet) but if you ignore your
condition, and let your insulating layers get soaked (even worse if your insulating
layer is down) then you are just plain being foolish and could end up paying a
very dear price for your lack of diligence in this area.
SYMPTOMS OF HYPOTHERMIA
If the above steps are not taken when it comes to heat loss and the human
condition, then symptoms begin to appear letting you know that your body is not
happy. Things are beginning to go downhill and one or more steps need to be
taken right away so that you can stop the downward spiral and get things back on
- Involuntary shivering.
- Peripheral body parts such as hands, feet, nose, ears, etc. Are becoming
numb due to body shutting down blood flow to conserve heat for the body's
- Dazed state of mind.
- Strange behaviour, demonstrated by poor choices when it comes to survival.
- Slurred speech.
- Loss of fine motor coordination - particularly in hands - You cannot zip up
your jacket because of vasoconstriction as mentioned above.
- Aggressive and uncontrollable shivering.
- Chalky/pale skin color.
- Dilated pupils.
- Aggressive shivering, followed by pauses, then back to shivering.
- Flexibility and movement reduced because of a lack of blood flow.
- Person curls up in a tight position in order to conserve heat.
(A windbreaker and/or wind pants are best made
from a material that does double duty of keeping
moisture out while letting moisture from within
escape. Fabrics such as Gortex@ work great).
Above are approximate Frostbite times for dry exposed unprotected flesh. Under
wet conditions, these times could change dramatically for the worse.
by excessive sweating when hiking or climbing. This really adds to heat loss due to evaporation, and even more so with the next
topic we are going to discuss. This is why layering is so important when is comes to clothing. Better to feel good when hiking and
stay dry, then to add more clothing just so you can stay warm when taking a short break. If you get your clothing all wet from
sweating, it will be very difficult to get it dry under cold and/or damp conditions in the mountains or any other outdoor location.
2) Just like with convection, using a windbreaker type shell will greatly slow down heat loss due to evaporation. Also, to add a little
sense to the first point just above, if you are done for the day, or if you are going to take an extended break, you need to adjust
your clothing by removing anything that is wet, and adjust your layering so that you are warm enough to be comfortable.
Sitting around in the snow, or on a freezing rock, is a good way
to get wet and experience a good bit of heat loss due to conduction. As the saying goes: "Stay Dry = Stay Alive"
4) Put on extra clothing (a jacket), or get into your sleeping bag so that you can insulate your body to prevent further heat loss due
to the adverse temperature gradient. Don't forget to protect your head with a good insulating hat (or better yet balaclava). Figures
have been quoted as high as 50% heat loss from your head and neck area. Carrying an extra hat or balaclava is a great lightweight
option for extra warmth.
5) Reduce the temperature gradient by applying some sort of exterior heat source. But this is not a practical option for us mountain
climbers. A more practical approach would be to get inside a tent and wait for our body heat to warm up the air inside.
HOW THE BODY RESPONDS TO HYPOTHERMIA
We have gone over much of the way the body handles cold,
but to recap all this, the body will do the following in order to
do what it can to protect itself from heat loss. As mentioned
above, the body is a chemical factory, and the reactions that
are required for life are very heat sensitive.
The body will also go into a mode where it will sacrifice
appendages such as hands and feet, etc. In order to preserve
precious heat for it's core organs like the heart, brain, and
lungs. This is why it will shut down blood flow to the
extremities. This being the case, you do not want to give
alcohol (or drink it yourself) if you are facing cold conditions.
Alcohol is a vasodilator and should be strictly avoided when
survival is at stake. Dilated blood vessels are subject to far
greater heat loss and this in turn can cool the body at an alarming rate. Many an alcoholic has died from exposure to cold due to this
principal. Caffeine is another substance to be avoided. It is a diuretic (pulls water out of the body). This will increase your risk of
dehydration and a slowed down circulatory system (due to lower blood volume). This in turn will aggravate a hypothermic condition.
Tobacco/nicotine is also on the avoid list. Nicotine is a vasoconstrictor (narrows the blood vessels) and this condition increases the
risk of frostbite. Now this may sound contradictory with the above statement about alcohol (which does the opposite), but things like
alcohol and nicotine are indiscriminate in their effect on the body. Meaning that alcohol will dilate vessels everywhere in the body,
and nicotine will constrict vessels everywhere. Far better to let your body decide which vessels to constrict and which ones to dilate.
Your body will always perform in a way that is best for your survival if not hampered by the above substances ("you are fearfully
and wonderfully made" Psalm 139:14).
Shivering is also a mechanism that the body uses to produce heat. Shivering is the body's way of putting the muscles to work so that
fuel is burned and heat is generated. Far better though to take preventative steps as outlined above, to reduce or stop heat loss,
before the body has to take such drastic measures. Shivering is a warning that the body is going into survival mode, and you need to
take measures to increase heat through activity, or put on some extra clothing to pull the body out of this type of activity.
Therefore, in conclusion, the two primary things the body does to combat cold (on it's own) is cutting the blood supply to the
extremities (to conserve heat for the core), and shivering in order to produce heat. (there are many other things the body does in reaction to
cold, but these are the most obvious and recognizable)
OTHER HYPOTHERMIC FACTORS
- Body fat composition. Heavier set people have greater body fat composition and therefore are better insulated.
- Fitness level. People who are more fit, generally have a better metabolism, and burn fuel at a greater rate. This produces heat.
They are also better off when it comes to survival, since they will be able to shiver for more extended periods of time.
- If you can stop further heat loss to the body, a person can increase their internal temperature at a rate of 3.6 degrees F./hour
by shivering. This is a substantial increase in body core temperature. But it requires a frightful amount of shivering. Thus, the
more fit an individual, the greater their chances will be to reverse their hypothermic condition using this method of operation.
- Exhaustion level. Worn out climbers, hikers, backpackers, etc. are much more susceptible to cold. This is because they have
used up all their ready reserves of fuel and energy. Muscles are less able to generate heat (due to the lactic acid build up), and
this tends to shut them down. For much more on this subject, see our article on Conditioning, and Outdoor Food.
- Hydration Level. Water intake and proper
hydration are not only critical when it
comes to hypothermia, but it is also vital to
every aspect of good health and disease
prevention. For the outdoor enthusiast it
plays a role in your energy production,
helps prevent altitude sickness, and is vital
in keeping your blood volume up and
circulating so that it can provide life giving
warmth and nutrients to every living cell in
your body. Water is also required by the
body to burn fuel. This fuel burning also
produces warmth. So make sure you are
- Fuel level. You need to eat properly. As
mentioned in the hydration section, fuel is
required by the body so that it can produce
heat. I find that good fats such as those in
nuts and olive oil, are fantastic when it
comes to long term sources of fuel
- Slow, intermittent, and/or weak pulse.
- Breathing becomes very shallow and very erratic.
- Victim is Semi conscious or appears dead.
- Cardiac arrythmias set in, this leads to ventricular fibruillation resulting in heart failure as the cause of death.
How to assess a hypothermic condition:
1) Ask the person to stop shivering. If they can then hypothermia is most likely mild.
2) If the individual is all curled up into a ball, try to open their arms. If the arms curl back into the original position then the person is
most likely still alive.
3) Check for a pulse. If you cannot find one and you know that the person is still alive, then it is a sign that the core temperature is
most likely less than 88 degrees F. This would put the individual in the severe hypothermic stage.
for the body during cold nights. During the day, quick energy producing carbohydrates work best. For much more on this
subject, see our Outdoor Foods section.
- Tight Clothing. Make sure that you do not over tighten things like your boots or draw strings on your clothing. Not only is
this uncomfortable, but it cuts off circulation This in turn puts that area of the body in greater danger of cold injury. This
factor, I believe, played a role in my getting frostbite. In our forced bivouac situation, I failed to loosen up my boots when
laying in the snow. This in turn greatly reduced the circulation to my feet, and I ended up with frostbite on my toes.
- Bad Decisions. This factor plays out in many ways. First of all, you can put yourself into a hypothermic condition by failing
to turn back on a summit bid. Failure to do so may land you into a forced unprepared bivouac (like what happened to me).
Therefore, the best time to correct your thinking and get back on track is before you find yourself shivering uncontrollably
because you failed to take necessary precautions. Later on decision making may not be so easy. During World War II, pilots
that flew missions during the winter were subject to very cold temperatures during their flights. When they returned to base
later on, ground crews found that the pilots were in varying states of hypothermia. Along with this, they also discovered that
the pilots thinking was compromised. It took a fair amount of time for them to regain their mental acuity. This plays into your
ability to correct your hypothermic situation big time. So the bottom line is this. You need to make good decisions before you
slip into a hypothermic state in the first place. Your life just may depend on it.
Obviously the best way to treat hypothermia is to prevent it.
But what do you do if you, or one of your companions, has
fallen into this condition? Over the many years that I have
been climbing, hiking, and backpacking in the mountains, I
have had several cases of mild hypothermia, with one more
serious case, where I got frostbite on Split Mountain in the
California Sierra Nevada. I have to tell you, that I made a
whole range of mistakes that led up to that injury. Hopefully I
have learned a few things when it comes to preventing and/or
treating this situation in the future.
Here few things to consider when it comes to the treatment of
- Eat easily digestible foods and oils like olive oil to provide fuel for
both short term and long term needs. This action is similar to throwing
a log on the fire.
- Fires are hard to come by in the wilderness, but if they are allowed,
and you have the fuel, then a fire is an incredible way of adding some
heat to the equation. However, I find that this is rarely necessary or
even practical when mountain climbing. If you have come prepared
and have the proper clothing, shelter, and food items, a fire should not
- Start up the stove, and heat up some cool-aid, soup, or other type of
liquid. This is a fantastic way to add much needed heat to the body
core and take in a bit of fuel at the same time.
- Stop further heat loss. Remove all wet clothing and exchange for dry if possible, and add additional layers if needed. This stops
radiation and conduction heat loss. If things are really bad, set up your tent or bivy bag, and get into your sleeping bag.
- Get out of the wind by either taking shelter in the tent, or if you have to be on the move, put on your protective outer shell that
should include both wind and rain protection (the shell should also be breathable to prevent moisture from building up due to
sweat later on if you are moving)
- Make sure to drink water to stay hydrated so that your blood volume stays up to par so that it can flow freely and help
distribute life preserving warmth to all areas of the body.
- Loosen up overtightened boots and draw strings on your clothes so that you are not cutting off circulation.
- Urinate. A full bladder is another area that the body supplies heat to, and warming up additional liquid in the body taxes the
system further. As the body constricts blood vessels in the extremities, more fluid is diverted to the bladder. However, there is
a fine balance here, because you also need to replace lost liquid to the vascular system as mentioned above. This is why
drinking warm fluids works so well. All this being said, it would not be a bad idea to throw a small container of fuel and a
super lightweight stove (and small pot) into your summit bag. It could turn out to be a lifesaver.
- If the individual is in really bad shape, you can apply heat to the major arteries in the neck, armpit, crotch and palms, using
hot water bottles. Or you could make strips of cloth from an article of clothing, pour warm water on them, and then apply the
warmed strips to the body parts as mentioned above. This gets much needed heat to critical areas of the body quickly. In very
cold conditions, you will need to reheat the strips over and over again if you are going to have any success in reversing the
condition of a severely hypothermic individual. You could also heat up some rocks, wrap them up, and then use them in a
similar fashion as indicated above. Rocks tend to maintain heat quite well. Obviously you will need some sort of heat source
(like a stove), and care must be taken so that you do not burn the patient.
- In life threatening situations, it may also
be necessary for another individual to get
into a sleeping bag with the severely
hypothermic individual. This method can
provide some long term heat that may not
be available by any other means. Also,
several individuals huddling together is a
much warmer situation than going it alone,
because you can greatly limit the exposed
areas of each individual by doing this.
- If you come across someone who is in a
fetal position, or who is semiconscious
(due to the cold), be very careful in
moving him or her. People in this state
could be killed if cold blood is sent to the
heart from the extremities. This condition
is know as "Afterdrop" It can best be
avoided by not rewarming the extremities
but by rewarming the core only.
Obviously, do not expose the individual
(or anyone for that matter) to extremes of
If you are any of your party members develop frostbite, there are a few things to remember while out in the field. First, as
mentioned above, stop further heat loss. Next, do not rewarm the affected area unless you are able to maintain proper warmth for
the entire rest of the trip. Frozen, thawed, and then refrozen flesh causes far greater damage than flesh that has only been frozen
once. If your feet are involved do not rewarm them if you have to hike out. Much less damage will be done if you walk out on a
frozen foot then if the foot is thawed out (not to mention the pain). When I got frostbite my companions carried all my gear so that I
I had as little weight as possible on my feet. Once back in civilization you need to get to a doctor or hospital right away. Let them do
any further rewarming or treatment.
Blisters often accompany frostbite and should not be broken. Breaking them could risk infection. They usually go away on their
own. Leave all additional treatment to your doctor. This is just a bit of advice while out in the wilderness and away from medical
help. Being helicoptered out is also an option in very serious cases.
Frostbite will not occur if the temperature is above 28 degrees F. This is because your intracellular fluid also includes salts. When the
fluid inside the cell freezes, the delicate balance of salinity changes and fluid is drawn into the cell. This eventually causes the cell to
burst causing both tissue damage and blisters to form in the affected area.
View of Mt Shasta from atop Mt Lason California
Mount Sill - Sierra Nevada
Wilson Peak - Colorado
|Abandoned Road in the San
Juan Mountains - Colorado
Cattle Ranch at the base
of the Sierra Nevada
Palisade Glacier - Sierra Nevada Mtns.
Aspens with early Fall Snow backdrop
along Bishop Creek, CA
Deep snow glissade on Split Mountain
Climbers camped at Sam Mack
Meadow - Mt Sill
Late Spring Snow - Sam Mack
Meadow - North Fork Big Pine
- result of forced
bivouac high up
Dallas Peak - San Juan Range in Colorado
Brice Canyon - Utah
Hypothermia, like just about every other
ailment that I can think of, is easier to prevent
than to treat. But if one is to avoid this
condition you need to use your head when
going out on frigid outdoor adventures. You
also need to be prepared. This means carrying,
and wearing proper clothing, including proper
shelter. Carrying adequate food, and drinking
proper amounts of water is also very important.
Doing all this will prevent just about every case
of hypothermia. I have tried to give you several
guidelines above, and I hope that they have
been helpful. I would also like to mention that
the information in this article is limited, and it is
not intended to be a complete or an end all on
the subject of hypothermia by any means. So
make sure to continue your education on this
subject and the many others involved in outdoor activities. Get all the training you can from qualified people in all area of wilderness
travel. By doing this, you will be better trained to avoid senseless injuries or even loss of life on your future journeys.
liquid material. Such materials have a much higher density, thermal conductivity, and heat capacity then air. This means that they
can carry heat away from the body much faster rate. Steel, for example, is very dense. And if a very cold piece of it should come
into contact with your skin, it could actually stick to it (causing you great personal damage). This is due to the instant loss of any
warmth (which has been transferred from your skin to the steel) through the process of conduction.
But the greatest danger for the outdoorsman is water. It is reported that water has a 20-25 times greater ability to conduct heat away
from the body than air does. Many people have died from hypothermia because of wet cold conditions due to this concept.
This is the most complex and least understood form of heat loss. Thermal radiation is transmitted through air and space. It’s a form
of electromagnetic radiation like light and radio but at a lower frequency. Radiation transfers heat from hot things like the sun or
embers in a fire, to colder things like your skin.
An example of this would be a sunny day on a glacier. The air temperature may be near freezing but if you turn your bare face to
the sun you can feel its radiant warmth. But if you pull off all your clothes, you’ll be unhappy. As it turns out, radiant heat is not
near as effective as conduction (discussed below). Cold air will cause hypothermia even on a sunny day.
Unfortunately, radiation also takes heat away from your body and transfers it to things that are even colder, like a snowfield or deep
space on a clear night.
How to take advantage of thermal radiation:
1) If you wear dark colored clothing (which absorbs more thermal radiation then light colors), you can utilize the solar radiation while still
avoiding conduction to the cold air.
2) A reflective surface, such a the thin mylar layer on the inside of an “emergency blanket” (also known as a “space blanket”) will
reflect some of your body’s thermal radiation back to you. My personal experience with space blankets in cold conditions is that this
warming effect is minor at best. I had one on Split Mountain and still ended up with frostbite.