Hypothermia
Nature’s
Silent Killer of the Unprepared
Warning and
Disclaimer
This
presentation is designed to be used in conjunction with training courses given
by medical personnel with experience in outdoor emergency medical response
providing training in this subject.
Since
the knowledge and expertise of such trainers cannot be gauged by the Gaelic
Wolf Outdoors team, we cannot accept responsibility for the quality of training
given in conjunction with this presentation set.
Many of the photographs used here were taken by David
Bassett in his travels through the North American West and Northwest, and are
being used with his permission.
More of David’s work can be seen on his WWW site at:
http://www.et.byu/~bassettd
What is it?
Hypothermia is a silent killer of those
who are not prepared to face a cool, wet day.
It happens when your body is not able
to make enough heat to replace the warmth you lose to the environment around
you.
If left untreated, hypothermia can kill.
Nobody ever froze to death – instead, they died of
hypothermia.
The freezing part came later...
...and only if the temperature of the surrounding
environment was below freezing.
Technically
Speaking
Hypothermia is a medical condition that results from the
body’s inability to adequately replace heat lost to the surrounding
environment.
It is a progressive condition that can be reversed with
appropriate care in the field.
YOU
have had it
before!
Have you ever felt cold?
Did you begin to shiver?
Did you shiver so hard that you couldn’t stop the shaking?
YES?
Those were the early stages of hypothermia!
The 1964 Four Inns Walk
Annual competitive hike over English moorlands – 45 miles
(73 km) long
1964 featured heavy rain, winds of 30 mph (48 km/h),
32º-45ºF (0º-7ºC) temperatures
240 experienced hikers started the day, 22 finished (usually
about 2/3 finish)
Three died of hypothermia, four rescued in critical condition
Four Inns
Lessons
Clothing typically provided less than 40% of the insulation
the hikers required
Most hikers took in 1000-1500 kilocalories (Cal) against a
need of 6000 Cal
All hikers had been selected for experience and top physical
condition...
...but most were unable to maintain a high enough energy
level to produce enough heat to keep adequately warm
What’s Next?
A short terminology review
How your body maintains its temperature
Avoiding hypothermia in the first place
How your body responds to cooling
Knowing how to recognize hypothermia
How to treat hypothermia
Immersion hypothermia – different from land hypothermia...
Terms to Know
CORE – Central organs of the body, most importantly the
heart, lungs, liver, brain
DISTAL – Away from the body’s center
HYPOTHERMIA – Lower than normal core temperature
HYPOTHERMIC – Having a lower than normal core temperature
HYPOXIA – Condition resulting from a lack of oxygen
circulating in the body
More Terminology
HYPOXIC – Having reduced oxygen levels in circulation
NORMOTHERMIC – Having a normal core temperature
PERIPHERY – “Outer” tissues and body parts, such as skin and
all the tissues of the arms and legs
PROXIMAL – Closer to the body’s center
Last of the
Terminology
VASOCONSTRICTION – Constriction or “narrowing” of the blood
vessels
VASODILATATION – Dilation or expansion of the blood vessels
Note: When discussing vasoconstriction and
vasodilatation in relation to how they play a part in hypothermia, we are
talking mostly about the blood vessels in the periphery
Normal Body
Temperature
Average oral temperature 98.6ºF (37ºC)
Normal range is from 96.5ºF (35.8ºC) to 100ºF (37.8ºC)
Varies 1¼º - 3¾ºF (0.7º - 2.1ºC) during any given 24 hour
period
Lowest in early morning hours, highest in late afternoon or
early evening
Average variation 2.7ºF (1.5ºC) for men and 2.2ºF (0.5ºC)
for women
Exercise Body
Temperature
Prolonged, heavy exercise can commonly cause the body
temperature to rise as high as 104ºF (40ºC)
If heat dissipation (by sweating) is impaired, higher
temperatures and their related heat illnesses (such as heat stroke) may
occur...
...even if the weather is cold
Controlling
Body Temperature
Physiologic responses – controlled by the brain
(involuntary, such as shivering and vasoconstriction)
Deliberate actions – (such as exerting yourself or putting
on layers of clothing to retain heat when you stop exercising)
Hypothermia
Weather
It’s cold. It’s
wet. I wish I was just about anywhere
else. I sure as heck didn’t sign on for
this!
The weather doesn’t have to be freezing for you to get
hypothermia. A 50°F (10°C) day with
wind and rain will do just fine, thank you very much!
Part of preventing hypothermia is knowing how your body
works, and how to protect yourself from the weather. Read on!
Responding to
the Cold Environment
The amount of heat you can generate through metabolism and
exercise is minimal in comparison to the rate you will lose heat in a cold
environment
You have to prevent heat loss
Unrelieved cold water immersion or low air temperatures and
wind without adequate protective clothing usually results in lethal hypothermia
Physiologic
Heat Loss
Heat is generated in the muscles and by metabolic chemical
reactions (mainly in the liver)
About 90 - 95% of this heat is lost through the skin
Some heat is lost through the lungs
Heat is transferred from where it is being produced to the
skin by warming the blood as it circulates through
Physiologic
Heat Loss (con’t)
Peripheral blood vessels dilate or constrict to control
blood flow and determine rate of heat loss.
Blood flow through fully dilated vessels is about 100 times
greater than through completely constricted blood vessels
Amount of heat transported is affected by the body’s total
blood volume
Physiologic
Heat Loss (con’t)
Heat loss rates are greatly increased by sweating,
especially in dry environments
Vasoconstriction is the most significant physiologic heat
loss control mechanism
Peripheral vasoconstriction allows a cool outer “shell” to
form – an insulating barrier that slows heat loss from the body core
Involuntary
Change in Heat Production (Shivering)
Involuntary shivering begins in response to a drop in the
body core temperature
Heat production roughly equal to that of a brisk walking
pace
DANGER! – Shivering usually stops once the core temperature
drops below 90º - 92ºF (30º - 31ºC)
DANGER! – Warming the skin of someone with hypothermia may
stop the shivering, even though the core temperature hasn’t changed.
Shivering
(con’t)
Much more heat is produced by performing useful work, such
as hiking out of the threatening environment to shelter
Shivering brings several hazards caused by its interference
with co-ordination
Alcohol, some medications, low blood sugar, and exercising
to exhaustion all hasten development of hypothermia by interfering with the
ability to shiver
Your
“Thermostats”
Dominant control is exerted by a control center in the brain
called the hypothalmus
Located at the base of the brain
Anterior portion of the hypothalmus is the “heat loss center”
Posterior portion of the hypothalmus controls heat retention
A secondary control function takes part in the skin
(cutaneous control mechanisms)
Information
Sources
Temperature of the blood circulating through the hypothalmus
Impulses from nerves in the skin
Information from both
generally integrated to initiate a physiologic response
However, there are exceptions...
Cold water
immersion results in shivering before core temperature drops
Shivering
stops as soon as the skin is warmed, even if the core temperature is still
dropping
Cold Adaptation
Homo Sapiens is a tropical animal
Peoples who live in cold environments have adapted to their
environment over time, and have an increased cold tolerance
People who grow up in temperate climates do not “cold-adapt”
to a point where they can gain anything like a significantly increased
resistance to hypothermia
We have to carry our tropical environment with us wherever
we go (clothing)
Cold
Vasodilatation – the “Hunting Reaction”
When hands are immersed in water cold enough to cause tissue
damage, blood vessels constrict to preserve heat
Every 7-15 minutes the vessels dilate, especially in
fingers, warming the tissues
Prevents hand and finger disabilities
Trade-off is a temporary increase in the rate of heat loss,
especially problematic in full-body cold water immersion
Best Option?
PREVENTION!
You have to prepare yourself for the worst the environment
can throw at you if you don’t want to have hypothermia
There are two things you can do:
– Reduce heat
loss
– Increase heat
production
Easy concepts
to remember, right?
They won’t help
you if you don’t apply them, though...
Environmental
Heat Loss
We lose heat to the environment in four ways:
Convection, conduction, evaporation, and radiation
In comfortable environments, about 65% is lost by radiation,
with most of the rest lost through evaporation
In cold environments, most of your heat is lost by
convection and conduction
Convection
Happens when air or water with a lower temperature than the
body comes into contact with the skin and then moves on
You use convection when you blow on hot food or liquids to
cool them
Amount of heat lost depends on the temperature difference
between your body and the environment, plus the speed with which the air or
water is moving
Convection
(con’t)
If you are not moving, and the air is still, you can
tolerate a cold environment quite well
Air in motion takes away a LOT of heat
With air in motion, the amount of heat lost increases as a
square of the wind’s speed
A breeze of 8 mph (12.8 km/h) will take away FOUR times as
much heat as a breeze of 4 mph (6.4 km/h)
Convection
(con’t)
Above wind speeds of 30 mph (48 km/h), the point becomes
moot, because the air does not stay in contact with the body long enough to be
warmed to skin temperature
Convective cooling is much more rapid in cold water because
the amount of heat needed to warm the water is far greater than the amount of
heat needed to heat the same volume of air
Conduction
Transfer of heat away from the body to objects or substances
it comes into contact with
This is the one where grabbing a door handle with a moist
hand at -40º gives you a chance to stick around...
Stones and ice are good heat conductors, which is why you
get cold when you sit on them
Conduction
(con’t)
We knew you might need a chuckle, and we had one available
to put here....
Now – be honest – how many of you gave this a try on a dare
when you were much younger and less wise than you are today?
Do you know how to get the metal to let go of your tongue?
A large-ish pot of warm water will do the trick
Before you go in to get one, though, you really ought to
tell the dare-ee not to kiss the pole in addition to the what he’s already
done...
Conductive heat loss in action!
Conduction
(con’t)
Air conducts heat poorly – still air is an excellent
insulator
Water conductivity is 240 times greater than that of dry air
The ground is also a good heat conductor, which is why you
need a foam pad or other insulating barrier under a sleeping bag if you want to
stay warm overnight
Conduction
(con’t)
Alcohol is an excellent heat conductor that remains liquid
well below the freezing temperature of water
At very cold temperatures, drinking alcohol (ethanol) can
result in flash-freezing of tissues inside the mouth
If the back of the throat and the esophagus become frozen
this way, the resulting injury is often lethal
Evaporation
Responsible for 20% - 30% of heat loss in temperate
conditions
About 2/3 of evaporative heat loss takes place from the skin in
thermoneutral conditions
Remaining evaporative heat loss happens in the lungs and
airway
In cold weather, airway evaporative heat loss increases as the incoming air is
humidified and warmed
Evaporation
(con’t)
In cold weather, 3 - 4 liters of water per day are required
to humidify inhaled air
1500 - 2000 kilocalories (Cal) of heat are lost in this way
on a cold day
This fluid loss, if not replaced, results in dehydration,
causing a lowered blood volume and increased risk of developing hypothermia
Evaporation
(con’t)
Wet clothing enhances heat loss
Sweat-drenched clothing conducts heat toward surface layers
of clothing
Wet outer clothing layers enhance heat loss to the
environment through evaporation
A combination of sweat-soaked inner clothing layers and wet
outer clothing can be quite lethal
Radiation
Direct emission or absorption of heat
Heat radiates from the body to the clothing, then from the
clothing to the environment
The greater the difference between body and environmental
temperatures, the greater the rate of heat loss
Clothing that adequately controls the rates of conductive
and convective heat loss will compensate for the radiation heat loss
What to Wear?
Clothing does not prevent very much of the radiation heat
loss
Only special-purpose vapor barrier clothing has much effect
on evaporative heat loss
In order to be considered adequate, cold and wet weather
clothing needs to reduce or eliminate conductive and convective heat loss
Adequate clothing traps layers of warm air next to your body
Layering
Wear clothing in easily removed layers
During warmer times of the day and while producing extra
heat through exercise, remove outer layers
DO NOT SWEAT! Sweat-dampened clothing loses much of its
insulating abilities and increases your level of evaporative heat loss
Layering
(con’t)
Remove gloves or mittens first, unless you need to wear them
to protect yourself from conductive heat loss (handling cold tools, for
instance)
Neck-warmers and scarves should come off next, followed by
headgear
Open your jacket at waist and sleeves, followed by unzipping
if still too warm
Layering
(con’t)
Finally, if you are still getting too warm, begin removing
clothing layer by layer until you reach a level where you are comfortably warm
without perspiring
When you slow down or stop, you need to add layers back on in
the reverse order
Put layers back on before you start feeling cool or cold –
otherwise, additional heat is needed to
warm your body again
Layering
(con’t)
Something important to remember – Each layer of clothing
needs to be slightly larger than the layer beneath it
If most or all layers are the same size, they compress the
still air space, causing a significant loss in the insulating value of the
clothing
PLAN IN ADVANCE! Make sure you pack the right sizes for your
best protection
Clothing
Materials
Wool is an excellent choice. It is durable, and insulates
well, retaining 80% of its dry insulation value even when dripping wet
Down is the best insulator for its weight, but only when it
is dry. Down loses almost all of its insulating value when it is wet
Down is the filler of choice for sleeping bags and outer
clothing in areas where relatively dry snow is the main precipitation – most
typically at high altitudes
Clothing
Materials (con’t)
Polyester fibers are used as substitutes for down in wetter
climates. They retain much of their insulating value when wet, but are heavier
Polyester insulating fiber materials, such as Polarguard® or Qualofil® are constantly improving, with new
products becoming available
Clothing
Materials (con’t)
Polypropylene is being used for fabrics such as Polar Fleece® that retain much of their insulating
qualities when wet
Needs to be laundered frequently, because it retains body
odor
Has a disturbing (especially after you have spent a lot of
money) tendency to melt if dried by itself in a dryer on high heat...
Clothing
Materials (con’t)
Vapor barrier systems are multi-layered fabrics that contain
an impermeable layer bonded to one or more layers of other types of fabrics
Designed to retard evaporation of moisture from insensible
perspiration and slow evaporative heat loss
Used in extreme cold weather sleeping bags and socks, for
the most part
Clothing
Materials (con’t)
Moisture often collects between the vapor barrier and the
body
If used in weather that is not extremely cold, so much
moisture can collect beneath the barrier layer that overall protection from
cold is significantly reduced
Vapor barrier systems are most beneficial in extreme cold
weather situations
A Word About
Jeans...
Cotton denim is just about the WORST fabric you can wear in
wet weather
If the cuffs of your jeans are out where they can get wet,
the wicking action of cotton carries the water upwards
Wet cotton denim in a breeze will transport heat away from
your body as much as 240 times as rapidly as dry skin in calm air
The fashion statement that can kill...
Keeping Hands
Warm
The body’s first response to cold is to constrict the
peripheral blood vessels, which means that fingers feel cold sooner than most
other body parts
Fingers are small cylinders, and mittens are the best way to
keep them warm
¼ inch (0.6 cm) of insulation in a glove finger is the most
protection you can add; thicker glove fingers won’t keep your fingers any
warmer
Hand-warming
(con’t)
Best protection for hands is provided by a three layer
combination:
1 – A thin inner glove made of silk or nylon
2 – A thick inner mitten made with wool, down, or other good
insulating material
3 – An outer windproof, water-repellent shell mitten with cuffs
that seal about mid-way up the forearm
Is your hat
rack warm?
The brain is very selfish – it demands heat, and it will
steal it from anywhere else in the body
The skull is near the surface, and conducts heat as readily
as any other hard material
The scalp is very thin, and richly supplied with blood
vessels
If you want your body to be warm, you have to keep your head
covered
Headgear
A wool hat is the best readily available option – those with
a synthetic liner help keep the “itchies” at bay
Polypropylene hats also insulate quite well
The hat needs to cover the scalp, ears, and the back of the
neck to prevent heat loss adequately
Hoods are less effective, since they do not fit as snugly as
a good hat
Underwear
“Long-johns” need to maintain a layer of insulation next to
the skin, even when wet
Wool and polypropylene are the two best materials for
meeting this goal
Wool is less expensive, and provides more warmth for equal
weight – however, many people are sensitive to wool in contact with their skin
Rain Gear
Your clothing needs to be kept dry – wet clothing loses
most, if not all, of its ability to help you retain your body heat
Good raingear has two properties:
It keeps
out the rain
It
“breathes”, allowing water vapor to escape
There are no fabrics available that do both perfectly,
although two types come close
Rain Gear
(con’t)
Laminates, such as Gore-Tex®, have two or more layers, one of which
has pores large enough to allow water vapor to escape, but too small to allow
liquids to penetrate
Tightly woven rainwear fabrics that have very small pores or
composite fabrics (one being cotton, which swells to fill pores) are actually
water resistant, but will not stand up to heavy downpours
Rain Gear
(con’t)
Water repellent sprays can be used to increase weather
resistance of fabrics, but they are no substitute for high quality rain wear
There are numerous rain gear products that are made of
completely waterproof materials, with vents to allow sweat to evaporate...
...But you will get wet from perspiration if you have
to wear them more than a few minutes
A Word About
Ponchos
Ponchos are waterproof, and can be worn loosely to allow
perspiration to evaporate
If the wind is blowing, though, the poncho will:
1 – Flap around, and allow you to get wet
2 – The air pressure inside the poncho will be slightly
lower than it is outside in the wind, and raindrops will be “sucked” up inside
the poncho, making you still wetter
Rain Gear
(con’t)
It is just as important to protect your lower body as it is
your upper body
Rain trousers should be made from the same material as the
top garment
However, impervious rain trousers are less of a risk than an
impervious raincoat, because legs perspire less than the torso
DANGER! Never wear jeans in the rain, either
as an outer garment or under rain trousers
Rain Gear
(con’t)
A raincoat hood needs to be large enough to cover your head
when you are wearing a cap, but needs to close snugly enough to keep water out
Seams, especially at shoulders, tend to leak and need to be
well-sealed – inspect frequently, re-sealing as often as needed
Avoid raincoats with seams on top of the shoulders
Rain Gear
(con’t)
Zippers need to have a flap that will cover them, with
fasteners to keep the zipper covered in any weather
Pockets need to be covered with a flap that will keep water
out
Cuffs need to be closable with snaps or Velcro® because:
Elastic cuffs ride up and can’t be adjusted
Knit cuffs get wet and stay wet
Footwear
The warmest boots we know of are the double vapor barrier
military boots known as “Mickey Mouse” boots
Composed of inner and outer rubberized layers, with
insulation in between
They have some disadvantages, though:
Soft, floppy, little foot or ankle support
Perspiration cannot escape – feet get wet and stay wet, even
if they are warm
Footwear
(con’t)
DANGER! Sports shoes, whether they are low or
high-top are NOT suitable for use when hiking or
backpacking at any time
They are not waterproof or water-resistant, and do not offer
adequate foot or ankle support
These types of shoes are, however, light to carry, and are
acceptable as “camp shoes”, if you wish to bring them along
Footwear
(con’t)
Leather is the best material for boots
It can be made hard enough to provide good foot and ankle
support
At the same time it can be made soft enough to be flexible
It is porous enough to “breathe”, allowing moisture to pass
through
It can be made waterproof with a number of different
products, such as Sno-Seal®
Footwear
(con’t)
Leather boots are flexible enough to allow for the swelling
you get in your feet after several hours of standing and walking
Boots used in cold weather or very rough country should be
constructed of all leather, with a soft lining
Combination leather-fabric boots (with the best fabric most
often being Gore-Tex®) are excellent for warmer weather use in less demanding
terrain
Footwear
(con’t)
Your boots need to be large enough to allow you to wear two
pair of socks comfortably without feeling tight on your feet
Boots that are too tight lose most of their insulating
ability, increasing chances of cold injuries, such as frostbite
Tight boots also compress superficial blood vessels,
compromising circulation, which also increases risk of frostbite
Footwear
(con’t)
If you are backpacking, you should bring along a pair of
high-top “camp shoes” so that you can give your boots a chance to dry out at
the end of the day
Change to dry socks when you arrive, as long as you can keep
your shoes dry
Place the socks you remove into your boots, top first, so
they can absorb moisture from the leather overnight
Footwear
(con’t)
You should wear an inner sock of cotton, which will “wick”
moisture away from your feet
Your pair of “oversocks” should be made of an absorbent
material that will also keep your feet warm – wool is best
For extremely wet weather, there are now Gore-Tex® socks available, which you can use as
an additional layer, so long as they don’t make your boots fit too tightly
Gaiters
Gaiters are sleeves that fit tightly to the outside of your
boots and extend up the leg, usually to just below the knee
Generally waterproofed fabric with a zip up the back
Useful accessory that keeps snow out of your boots, water
from the trouser cuffs
Can give you a few extra seconds to get your feet out of the
stream you step into
Shelter
Home, sweet home...
Shelter
Temporary shelters, including tents, have to provide
protection from the convective cooling effect of the wind
Tents are not windproof, and need some kind of windbreak
placed between them and the wind
Well-constructed snow shelters are much more effective,
since they are much more effective at blocking the wind
Shelter (con’t)
Stationary air inside an effective shelter can be warmed by
body heat for a more comfortable environment
If your shelter is a natural cave with adequate ventilation,
you can build a fire for warmth
If you are in a snow shelter, and have built in good ventilation,
you can use a small stove for heat, as well as for cooking
Shelter (con’t)
If you use a tent in cold weather, you have to make certain
the floor and lower walls are waterproof
The inner walls of the tent must be able to “breathe” to
allow exhaled moisture to escape
You need an insulating pad between yourself and the ground
or any shelter floor directly in contact with the ground
Shelter (con’t)
Exhaled moisture freezes to the inside of tent walls – don’t
brush up against them (especially when you are changing your innermost
shirt...)
The inner walls of snow shelters will have some melting
until a thin layer of ice forms over the walls and ceiling – be sure to form
your ceiling so that it doesn’t have any “drip points”
Your Body’s
Heat Production
The only way to significantly increase your body’s heat
production is with exercise
The large muscles of the leg produce more heat than smaller
muscles elsewhere
If you are in a situation that prevents your using those
muscles to hike you out to a nice warm building, repeated exercise, such as
stepping up and down a rock will produce far more heat than shivering
Heat Production
(con’t)
The body produces heat as a by-product of the biochemical
reactions that convert food to stored
energy
During physical activity, only about 20% of this energy is
used for work – the rest is converted to heat
Energy from metabolizing food is expressed in kilocalories
(Cal), which are commonly erroneously referred to as “calories”
Heat Production
(con’t)
In everyday average activity most people require 1800-3000
Cal daily, depending on body mass and the type of work they do – with very
physically demanding jobs requiring more
Glucose is the major source of energy for the body, and is
stored in the liver, muscles, and (to a lesser extent) in the blood
Heat Production
(con’t)
Glucose is stored mainly in the form of glycogen
The body’s reserves are limited, adequate only for a few
hours before needing to be replaced
In cold weather, backwoods activities in poor weather may
require 6000 Cal daily
If you are depending on exercise-produced heat to avoid
hypothermia, you need to consume large quantities of food
Heat Production
(con’t)
Experienced outdoors users have found that repeated small
snacks in addition to at least three good meals a day will help keep
hypothermia at bay indefinitely
A balanced diet, with larger than usual quantities, is
essential for the best possible health during outdoor activities
Experience will teach you your personal best eating pattern
and food preferences
Oxygen
Consumption and Hypothermia
O2 consumption for a given level of work is greatly increased
when the body’s core temperature drops below normal
At rest an average man consumes 0.2-0.33 liters of O2 per minute (LO2/min)
Walking on level ground at 3 mph (5 km/h) consumes about 1.1
LO2/min
International class runners can achieve levels of 5.5 LO2/min for a short time
Oxygen
Consumption and Hypothermia (con’t)
Mount Everest expedition climbers work at about 1.45 - 1.98
LO2/min, with maximal consumption levels
of 2.0 - 3.75 LO2/min
Consumption of 2.5 LO2/min is about the same as producing 600
Cal/hour – or the same as trotting along at 6 mph (10 km/h)
After a core temperature drop of only 1.1°F (0.62°C), with
no work being performed, O2 consumption increases by 360%
Oxygen
Consumption and Hypothermia (con’t)
Research shows that hikers spontaneously increase their pace
whenever their skin temperature falls below comfortable levels
The resulting pace has been known to exhaust the hikers to
the point of near collapse
Poorly conditioned hikers may not be able to maintain such
energy expenditure levels long enough to get out of trouble
Physiologic
Cooling Responses
Human function is the end result of many complex chemical
reactions
Biochemical reaction times are extended when taking place at
less than optimum temperatures
Body functions become slower and less efficient
Blood thickens when cooled
Pliable materials, such as plastic, become stiff when cooled
– so do muscles
Cooling
Responses (con’t)
Cold doesn’t affect all organ systems the same, but can
cause one system to fail, bringing about failure in others
Until core temperature reaches about 90°F (32°C) the
response to cooling is mainly an effort to restore normal temperature
Below 90°F (32°C) function becomes more and more abnormal as the core continues to
cool
Cooling
Responses (con’t)
Mild cooling causes muscle stiffness and problems with
coordination
Oxygen consumption greatly increases, even when performing
simple tasks
Profound hypothermia slows nerve impulse transmission,
compounding coordination problems
Muscles lose the ability to contract or relax effectively
Cooling
Responses (con’t)
As cooling continues the victim’s muscle control
deteriorates to the point where no useful work, even so much as zipping up a
jacket, can be performed
Profound hypothermia victims often can’t even assist in
their own rescue
Shivering tapers off or ceases as the core temperature falls
through about 90°F (32°C), further reducing heat production
Cooling
Responses (con’t)
With mild cooling, thinking and the ability to make
appropriate decisions begin to deteriorate
Personality becomes disagreeable, with apathy and lack of
cooperation
As core temperature drops, impairment become more
significant, with confusion, disorientation, and complete inability to make
logical decisions
Cooling
Responses (con’t)
If still capable of coordinated movement, victims of extreme
hypothermia often take off clothing
Speech is slurred
As core temperature continues to drop, lethargy and
somnolence (drifting in and out of consciousness) progress to coma
Loss of vision can occur just before coma
Cooling
Responses (con’t)
One of the few good points of accidental hypothermia is that
the cooled brain requires far less oxygen than it does at normal core
temperatures
In cold-water drowning, this often means successful
resuscitation after extended periods of time under the water
Cooling
Responses (con’t)
Assume that all hypothermia victims are severely dehydrated,
with significantly reduced blood volumes
Vital organs with inadequate blood supplies work less
efficiently, compounding all the other problems that hypothermia causes
As core temperature drops, the kidneys extract still more
fluid as a result of what is known as “cold diuresis”
Cooling
Responses (con’t)
As fluid levels drop, the peripheral blood vessels constrict
even more than before, which forces cooler blood toward the body core
This increases fluid pressure in the core, more antidiuretic
hormone is released, resulting in still more urine production
Finally, cold and reduced O2 supply affect the kidneys, causing
more water loss
Cooling
Responses (con’t)
Blood volume is also reduced when core temperature drops
because water leaves the blood and is held in body tissues
Blood viscosity (thickness) is increased by as much as 175%
through fluid loss and the direct effect of cold on the blood
A core temperature drop also causes the spleen to contract,
increasing the number of circulating red blood cells
Cooling
Responses (con’t)
People who have been exposed to several days of cold often
have a reduction of as much as 25% in their blood volumes
This, coupled with the constriction of the peripheral blood
vessels, decreases the amount of oxygen transported to tissues
Oxygen transfer at the cell level is also impaired because
cold hemoglobin does not readily release its oxygen
Cooling
Responses (con’t)
Diminished oxygen delivery is partially offset by two
things:
Increased quantity of oxygen dissolved in the liquid part of
the blood (19% more at a core temperature of 76°F (30°C))
Tissue acidosis increases the rate of oxygen release from
the hemoglobin
Cooling Responses
(con’t)
In profound hypothermia, the heart beats slowly and weakly
(the muscle tissue becomes weak and stiff)
The amount of blood pumped with each beat is markedly
decreased
Impulse conduction is impaired, and the heart rate falls to
as slow as 20 or less per minute
Cooling
Responses (con’t)
Electrical conduction becomes erratic, and the heartbeat can
become irregular
As the core temperature continues to fall, a fatal
irregularity, ventricular fibrillation, can stop all circulation, causing the
victim’s death
Rough handling of a victim of severe hypothermia can trigger
ventricular fibrillation
Cooling
Responses (con’t)
Surprisingly, a hypothermia victim usually has a normal
blood pressure, although it may be hard to obtain a reading as a result of
diminished blood flow in the arm
Ventilation of the lungs is normal down to a core
temperature of about 90°F (32°C)
Below that temperature, carbon dioxide (CO2) begins to build up in the blood, an
indication of inadequate ventilation
Cooling
Responses (con’t)
As core temperature continues to drop, the brain becomes
more unresponsive to the increasing CO2 levels
Hypothermia can sometimes increase the secretion of mucus by
membranes lining the major airway passages, while the cough reflex may be
reduced, allowing a fluid build-up that can lead to problems
Cooling
Responses (con’t)
During re-warming, the lungs may fill with fluid (pulmonary
edema)
When autopsied, the lungs of people who have died after an
episode of hypothermia always show various types of damage, including:
Breakdown of alveoli (air sacs)
Bleeding
Fluid accumulation (edema)
Pneumonia (secondary to hypothermia)
Cooling
Responses (con’t)
Cooling the liver slows biochemical activity, but doesn’t
damage the organ
Drug metabolism in the liver is impaired, though, with a
medication’s effect often lasting much longer than normal
Giving medications at the prescribed dose and times can lead
to an inadvertent overdose
Cooling
Responses (con’t)
Effectiveness of insulin for diabetics is reduced during
hypothermia
Increased blood glucose levels are not uncommon in
hypothermia victims, even those who are not diabetics
Despite the many changes that occur in body systems during
hypothermia, hypothermia itself causes no permanent problems in an otherwise
healthy person
Complications
While the risk of complications is low in healthy people,
there are a few to be aware of
Most of these result from pre-existing health problems
1 – Pneumonia
2 – Acute pancreatitis
3 – Intravascular clots (thromboses) causing heart attacks
or strokes
Complications
(con’t)
4 – Pulmonary edema
5 – Acute renal failure due to tubular necrosis
6 – Increased renal potassium excretion leading to alkalosis
7 – Hemolysis (breakdown of red blood cells)
8 – Depressed bone marrow function
Complications
(con’t)
9 – Inadequate blood clotting
10 – Low serum phosphorus
11 – Seizures
12 – Hematuria (blood in the urine)
13 – Myoglobinuria (muscle pigment that looks like blood in
the urine)
14 – Simian deformity of the hand
15 – Temporary adrenal insufficiency
16 – Gastric erosion or ulceration
At Risk
Situations
On average the very young and the elderly are more likely to
develop hypothermia
The elderly may be malnourished or have debilitating
diseases
A room temperature of 60°F (16°C) may be inadequate to
prevent chronic heat loss in an elderly individual
Very young children have a proportionally greater body
surface area, and will lose heat more rapidly than older children
At Risk
Situations (con’t)
Alcoholics are one of the groups at highest risk for
developing hypothermia because:
Excess alcohol interferes with shivering
Alcoholics are often malnourished
Heat loss rates are increased because alcohol dilates the
peripheral blood vessels
Alcohol intake causes dehydration
At Risk
Situations (con’t)
Unprotected immersion in water cooler than 60°-70°F
(16°-21°C) places you at risk of developing hypothermia
Injured people are more likely to develop hypothermia than
healthy people due to shock or other complications caused by their injuries
Hypothermia can develop rapidly if you are immobilized
involuntarily or voluntarily
At Risk
Situations (con’t)
Adverse weather conditions (high winds, low temperature,
precipitation) set you up for hypothermia unless you are dressed adequately,
are adequately hydrated, and have been taking in enough food
All else being equal, you will survive longer on a 10°F
(-12°C) day with sunshine and still air than you will on a 40°F (4°C) day with
rain and wind
Recognizing
Hypothermia
Failure to recognize and treat hypothermia can have
devastating consequences
You need to watch both yourself and the people with you for
the development of hypothermia signs and symptoms
If one member of your group has obvious hypothermia, you can
assume that other group members have milder forms of hypothermia
Mild
Hypothermia
The victim complains of feeling cold
He or she is often wet...
...and is frequently shivering to some extent, though this
may not be apparent while walking
There is a loss of interest in any activity beyond getting
warm, and a lot of negativity toward the group’s original goals
Mild
Hypothermia (con’t)
Problems begin to develop with muscular coordination,
beginning with fine motor tasks in the hands
The victim gradually becomes unable to keep up with the
group and begins to have trouble walking over rough terrain
As the core temperature continues to drop, stumbling becomes
frequent, and he or she becomes clumsy with any task
Profound
Hypothermia
Defined as hypothermia with a core temperature of 90°F
(32°C) or lower
Characterized by altered mental function
Carelessness about protecting self from the cold
Thinking is slow; decision-making is difficult and often
erroneous
Memory for specific facts deteriorates
Profound
Hypothermia (con’t)
The victim may have a desire to escape the situation by
sleeping
Lapses in willingness to survive; wants to give up and sit
down
As the core temperature deteriorates, periods of
unresponsiveness alternate with periods of activity
Begins to drift in and out of consciousness until lapsing
into coma
An abnormal behavior pattern that seems to be specific for
profound hypothermia is the individual who appears willing to cooperate, but
fails to do so
Muscle function deteriorates in pace with declining mental
function
Shivering gradually decreases and finally stops at a core
temperature of about 90°F (32°C), although this varies by individual
Problems with walking progress to difficulty with standing,
and to becoming unable to do either
Skin may feel cold and unpliable, and may be pale or
slightly bluish (cyanotic)
There may be evidence of frostbite
There are no changes in the eye pupils
Pulse is often weak and hard to feel, slow, and irregular
Blood pressure is difficult to measure and is normal or
(rarely) low
Heart sounds may be diminished in intensity
Breathing tends to be slow and shallow
Lung sounds are usually clear, but may be changed due to fluid in the lungs
Breath may smell fruity due to incomplete metabolism – this
sign indicates a very serious situation
Clothing may be soaked with urine
Five most common signs of hypothermia
1
– Mental changes
2
– Incoordination
3
– Cold skin
4
– Acetone odor on breath
5
– Urine-soaked clothing
Near Death
Some victims of profound hypothermia have been pronounced
dead before they really were
Profound hypothermia can mimic death
An ECG may be required to determine if there is any heart
activity
No one should be pronounced dead until they have been
carefully rewarmed to near normal core temperature without successful
resuscitation
Treating
Hypothermia
No previously healthy
person should die of hypothermia after being rescued and having treatment
started
Although no two cases of hypothermia are alike, the
principles of case management are
Acute immersion hypothermia and chronic exposure hypothermia
are treated the same
Treating Mild
Hypothermia
(Above
90°F (32°C))
Protect from further cooling and rewarm by any convenient
means
If placed in a warm environment this group of hypothermia
victims will rewarm with no complications
If clothing is wet, it needs to be removed and replaced with
dry clothing
Warm (body temperature) liquids may be given by mouth, even
though they have virtually no warming effect
Treating Mild
Hypothermia
(con’t)
Alcohol of any sort should not be given to any hypothermia
victim
Heat sources such as hot water bottles, heating pads, or
warm stones may be used as external heat sources, and should be placed at
points of least insulation (inguinal areas, trunk, neck)
A second person in a sleeping bag can provide additional
warmth
Treating
Profound Hypothermia
Mortality of hypothermia profound enough to produce coma
varies from 50% - 80%, even with hospital care
When death occurs during treatment, it is invariably due to
ventricular fibrillation
This VF virtually never reverts to normal spontaneously, and
usually cannot be stopped, even with cardioversion, in severely hypothermic
patients
Treating
Profound Hypothermia (con’t)
The fundamental principle of care for deep hypothermia is to
avoid ventricular fibrillation while slowly rewarming the patient
There are many things that can trigger ventricular
fibrillation (VF) in victims who have profound hypothermia
Sudden exertion after long periods of being inactive can
cause sudden death by VF
Treating
Profound Hypothermia (con’t)
When the victim moves after a long period of inactivity, the
muscle action pumps cold blood back toward the heart
This causes the temperature of the already cold-compromised
heart to drop further, triggering ventricular fibrillation (VF)
The victim with profound hypothermia must never exert
himself – he must not walk, climb, swim, or even move when lifted
Treating
Profound Hypothermia (con’t)
Rescuers can trigger VF through rough handling of the
hypothermia victim
Manipulating the victim’s limbs can pump cold blood back
toward the heart, which can reduce its temperature enough to trigger
ventricular fibrillation
Patients with profound hypothermia need to be handled as
gently as they would if they had a spinal fracture instead
Treating
Profound Hypothermia (con’t)
Rescue will be futile if not carried out very gently
A hypothermia victim who has been cold for long enough to be
in this situation suffers little adverse effect from the additional minutes
involved in gentle handling
Victims of profound hypothermia should not be re-warmed in
the field unless there is no other alternative
Treating
Profound Hypothermia (con’t)
Rapid re-warming, by immersion in a warm water bath, can
cause “rewarming shock” which is often lethal
This can happen in profound hypothermia victims who are also
severely dehydrated (a common combination)
The warmth from the water causes blood vessels that were
constricted to rapidly dilate
Treating
Profound Hypothermia (con’t)
This results in a rapid fall in blood pressure and shock
Cold, metabolically imbalanced blood is shifted to the
heart, causing a further core temperature drop and sometimes triggering
ventricular fibrillation
Even though these mechanisms are not very well understood,
their predictability has been observed too often to ignore
Treating
Profound Hypothermia (con’t)
Treatment with heated, humidified air or oxygen has received
attention in recent years
The technique can be useful, but has some limitations to
keep in mind
Most of the heat is carried in the water used to humidify
the gasses
The total amount of heat carried into the core is not very
significant
Treating
Profound Hypothermia (con’t)
Since profound hypothermia victims only breathe shallowly
and slowly, the amount of overall heat exchange is further limited
For heated oxygen therapy to be effective, the gasses need
to be administered via an endotracheal (ET) tube...
...But inserting an ET tube can trigger our old enemy,
ventricular fibrillation
Treating
Profound Hypothermia (con’t)
If the oxygen is being administered via a bag instead of a
pressure demand valve, overventilation can occur, resulting in respiratory
alkalosis, maybe leading to VF
Rescuers may think they are providing more effective
treatment than they really are, leading them to fail to provide better
protection from the cold and more timely evacuation to hospital care
Treating
Profound Hypothermia (con’t)
Despite the limitations, systems that give heated,
humidified air or oxygen are useful, though best employed in the hospital
setting
The system can prevent heat loss via the respiratory tract
and add about 10 Cal / hr to the treatment process
A calorie saved is a calorie that doesn’t have to be added
later
Treating
Profound Hypothermia (con’t)
1 – The victim must NOT be allowed to move
2 – Evaluate for open airway, breathing and circulation
3 – Examine the victim carefully for signs of any other
injury or medical problem
4 – Remove from environment and prevent further heat loss
by:
Treating
Profound Hypothermia (con’t)
Gently remove wet clothing and replace with dry clothing
If you have a tent available, set it up – put the victim
inside with other people (heat)
Cover victim with any available sleeping bag, ground cloths,
raincoats, blankets
Head, neck, and trunk must be well covered
Loosen boots and constricting garments
Insulate the victim from the ground
Treating Profound
Hypothermia (con’t)
Review the four mechanisms of heat loss (convection,
conduction, radiation, and evaporation) to make sure you have not overlooked
any way the victim can lose more heat
If possible, build a fire – NEVER PLACE THE VICTIM CLOSE TO
A FIRE! – The other members of the group will need its heat to prevent problems
of their own
Treating
Profound Hypothermia (con’t)
5 – Plan and set up a definitive camp
If possible, move any other original camp to where the
victim is
If the camp cannot be set up where you are, locate a safe,
sheltered site very nearby
Once the new camp is set up, you can move the victim to it –
gently
Carry the victim to the new site on a litter (you can make
one from pack frames)
Treating
Profound Hypothermia (con’t)
DO NOT CARRY THE VICTIM ON THE BACK OF ANOTHER PERSON!
In shelter, there needs to be at least one person with the
victim at all times to keep the patient from moving and to provide some warmth
from body heat
When applying body heat, there should be as little clothing
between the patient and care-giver(s) as possible
Treating
Profound Hypothermia (con’t)
6 – Improve the quality of the shelter you are providing for
the patient
A tent will do if nothing better is available
Snow caves or other types of shelters that the wind can’t
get through are better
Heat the shelter with more than just body heat
You can use a stove unless you are in a tent or there is a
lack of ventilation
Treating
Profound Hypothermia (con’t)
You can heat tents with well-wrapped rocks you have heated
in your fire outside
Body to body contact (under the covers) should to be used to
provide warmth to the victim
(Society’s “rules” versus the need to save a life comes into
play ...)
Treating
Profound Hypothermia (con’t)
IF the victim is not re-warming after two hours AND rescue is distant, added heat should
be gently applied to the trunk with heated stones or hot water containers
Wrap the heated objects so they will not burn the patient
7 – Cancel all other plans – a victim of profound hypothermia
needs hospital care as soon as possible
8 – Plan for a rescue and send for help
Treating
Profound Hypothermia (con’t)
There are some advanced life support measures that are
appropriate for field and hospital care of patients with profound hypothermia.
However, these skills and techniques should be accomplished only by rescue or
hospital personnel who are specifically trained and certified for the necessary
procedures. Professional medical personnel who are at least ACLS / ATLS
certified may request the version of this presentation that includes a few
slides that refer to these techniques
Immersion
Hypothermia
While immersion hypothermia is most often thought of in
terms of water-based activities, all of us who are active in the outdoors are
vulnerable.
Will he make it, or will he fall in? Is there a pool behind
him? Are there obstacles there that can trap him?
Are you ready to be dunked in that numbingly cold water?
Immersion
Hypothermia
In relation to hypothermia, cold water has two specific
threat characteristics:
Extreme thermal conductivity (the rate at which it can
conduct heat away from you)
The specific heat of water (the large amount of heat needed
to raise water temperature)
These, plus water’s ability to penetrate clothing, make
immersion hypothermia a potential hazard to outdoor activities
Immersion
Hypothermia (con’t)
As in any other outdoor activity, preventing immersion
hypothermia is by far the best way to take care of the problem
You need to prepare yourself to prevent hypothermia relative
to the temperature of the water you may fall into and the activity you are
taking part in
Wetsuits are an obvious choice for surfing, board sailing,
and whitewater activities
Immersion
Hypothermia (con’t)
Choices are less obvious for such activities as fishing and
flatwater canoeing on a warm day
Be prepared for the worst, and dress for the dunking if
conditions make a swim more likely
Personal floatation devices (PFDs) should be worn for all
cold or roughwater activities
Immersion
Hypothermia (con’t)
Increase your food intake to match the worst that can happen
to you (a swim in cold, rough water will burn a LOT of calories...)
Never allow yourself to get dehydrated for any reason
No matter how warm it is above the water, you keep on
wearing that PFD! If you get dumped in, it keeps you afloat, and helps slow
heat loss from the trunk
Immersion
Hypothermia (con’t)
PFDs with large closed cell chest pads, closed with a zip-up
front can decrease cooling rates by about 30%
Well-constructed floatation jackets can decrease heat loss
rates by 40%-50%
Full-body cold weather survival suits can increase predicted
cold water survival times by as much as 4-5 times that for unprotected people
Immersion
Hypothermia (con’t)
When you are suddenly immersed in cold water, several things
happen:
Blood pressure can rise rapidly due to the constriction of
the peripheral blood vessels
Your heart rate may increase as a result of fear or panic
People with heart defects or cardiac illness may develop
lethal abnormalities
Immersion Hypothermia
(con’t)
Immersion hyperventilation is the first risk...
The first few seconds of immersion in cold water bring a
breathing pattern of deep, involuntary gasps
This is followed by a minute or more of deep, rapid breaths,
with tidal (breathing) volumes about five times normal
Drowning can easily happen in this early stage, especially
if you are plunged deep below the surface, or fall into rough water
Immersion
Hypothermia (con’t)
With hyperventilation comes alkalosis
You lose larger than normal amounts of carbon dioxide,
reducing the blood levels of CO2, and increasing the blood’s pH
Physiologic responses to alkalosis cause a reduction in
blood flow to the brain
Dizziness or fainting can result, increasing your chances of
drowning
Immersion
Hypothermia (con’t)
In water temperatures around 60°F (15°C) you can only hold
your breath about a third of the time you normally can – this increases the
chances of drowning if you go under the surface for more than a few seconds
When you hit the water, the peripheral blood vessels
constrict immediately, and this forms a body “shell” that helps slow core
cooling
Immersion
Hypothermia (con’t)
However, there are some problems with this “tissue
insulation”...
As the muscles cool, nerve impulses are slowed, resulting in
slow, weak, poorly coordinated movements
This makes treading water or swimming much more difficult
than normal
Dysfunction increases as the tissues cool, causing inability
to swim or tread water after 10-15 minutes in 50°F (10°C) water
Immersion
Hypothermia (con’t)
When this stage is reached (in as little as five minutes in
icy water) the victim is no longer able to assist in his or her rescue
In such cases, a rescuer has to be prepared to enter the
water with the victim if the rescue is to succeed
Hypothermia does not cause deaths early in cold water
immersion emergencies – these deaths result from either drowning or cardiac
arryhthmias
Immersion
Hypothermia (con’t)
However, most people immersed in cold water survive this
initial stage
If you have the time to exercise the choice, enter cold
water as gradually as possible
DANGER! –
NEVER dive into cold water!
Consciously control your breathing, if at all possible,
during entry and for the first few minutes afterward, until the feeling of not
being able to catch your breath is gone
Immersion
Hypothermia (con’t)
After 10-15 minutes of immersion, shivering is constant and
obvious to observers
The emotional reaction to the situation can cause feelings
that can’t be appreciated until you’ve “been there, done that”
At this point the body core has NOT begun to cool – that starts at the
15-20 minute mark in cold (50°F (10°C))
water
Shivering may temporarily prevent heat loss in dry air, but
not in cold water
Immersion
Hypothermia (con’t)
Once the core begins to cool, the rate of cooling depends on
the temperature of the water
Differences in body build have an effect on cooling rates in
cold water, with body fat being the main variable
Generally, doubling the skin fold halves the cooling rate
Immersion
Hypothermia (con’t)
Water Temperature Cooling Rate
°F °C °C / hr
__________________________________________
68 20 0.5
59 15 1.5
50 10 2.5
41 5 4.0
32 0 6.0
Immersion
Hypothermia (con’t)
Alcohol is a feature of many water mishaps, mainly by
increasing the chances of a person accidentally entering the water
Blood alcohol concentrations below a level of 0.10g/100ml do
not significantly affect the rate of cooling
Higher concentrations result in higher cooling rates as a
result of the dilating effect on the peripheral blood vessels
Immersion
Hypothermia (con’t)
Once immersed, swimming is a dangerous choice to make
An average person who can ordinarily swim well probably will
not be able to swim more than 1 km (.062 mi) in 50°F (10°C) water on a calm day
People who tread water lose heat about 30% faster than
people holding still while wearing a PFD
Immersion
Hypothermia (con’t)
Any motion you make while you are in cold water takes heat
away from you much more quickly than holding still
Huddling with one or more other people will reduce heat loss
rates by about a third, especially if chest to chest contact is maintained
Holding the top of the PFD in your hands and raising your
knees to your chest will also reduce your heat loss rate
Immersion
Hypothermia (con’t)
Make every effort to get out of the water
Even getting only the upper body out of the water greatly
reduces the cooling rate
You may feel colder when you get at least part of yourself
out of the water, but research shows that full immersion in cold water produces
a much faster rate of core cooling
Immersion
Hypothermia (con’t)
A positive attitude and will to survive are very important
in cold water immersion incidents
It will not extend survival times beyond those
dictated by the water and your body
It will
help prevent you from giving up
Knowledge of how immersion hypothermia works and being
prepared will definitely help you to extend your survival time
Afterwords
There is a LOT to know about hypothermia, how it develops,
how to prevent it, how to recognize it in yourself and others, and how to treat
it when all else fails
Hypothermia is one outdoors killer that we can tame
The amount of knowledge you take away from this presentation
and build into your outdoor living will determine how safe you are in the
outdoors – or not...
Want to learn
more?
We recommend the book, Hypothermia,
Frostbite, and Other Cold Injuries by Wilkerson, Bangs, and Hayward. You
can get this book at many outdoors stores, or you can order it directly from
The Mountaineers at:
http://www.cyberspace.com/mtneers
Please forward any questions comments, suggestions for
improvement, or requests for correction to:
gaelwolf@ssnet.com