States Search and Rescue Task Force
and Cold Weather Injuries
How We Lose Heat to
- Radiation - loss of heat to the
environment due to the temperature gradient (this occurs only as long as the
ambient temperature is below 98.6). Factors important in radiant heat loss
are the surface area and the temperature gradient.
- Conduction - through direct
contact between objects, molecular transference of heat energy.
Water conducts heat away from the
body 25 times faster than air because it has a greater density (therefore a
greater heat capacity). Stay dry = stay alive! Steel
conducts heat away faster than water.
Example: Generally conductive heat
loss accounts for only about 2% of overall loss. However, with wet clothes the
loss is increased five times.
- Convection - is a process of
conduction where one of the objects is in motion. Molecules against the
surface are heated, move away, and are replaced by new molecules which are
also heated. The rate of convective heat loss depends on the density of the
moving substance (water convection occurs more quickly than air convection)
and the velocity of the moving substance.
- Wind Chill - is an example of
the effects of air convection, the wind chill table gives a reading of the
amount of heat lost to the environment relative to a still air temperature.
- Evaporation - heat loss from
converting water from a liquid to a gas
- Perspiration - evaporation
of water to remove excess heat
- Sweating - body response
to remove excess heat
- Insensible Perspiration
- body sweats to maintain humidity level of 70% next to skin -
particularly in a cold, dry environment you can lose a great deal of
moisture this way
- Respiration - air is
heated as it enters the lungs and is exhaled with an extremely high
- It is important to
recognize the strong connection between fluid levels, fluid loss,
and heat loss. As body moisture is lost through the various
evaporative processes the overall circulating volume is reduced
which can lead to dehydration. This decrease in fluid level makes
the body more susceptible to hypothermia and other cold injuries.
Response to Cold
Cold Challenge - (negative factors)
- Wet (rain, sweat, water)
- Wind (blowing, moving, e.g.
Total = Cold Challenge
Heat Retention - (positive factors)
- Size/shape (Eskimo vs. Masai)
- Insulation (layering/type)
- Fat (as insulation)
- Shell/core (shunt blood to core)
shell acts as a thermal barrier
Total = Heat Retention
Heat Production - (positive
- Exercise, shivering Limited by:
- Fuel stores (glycogen)
- Fluid status (efficient
- Food intake (kindling,
Total = Heat Production
Surface to Volume ratio
Shell to Core shunting
Your Body Core
1. Heat is both required and
produced at the cellular level. The environment acts as either a heating or a
cooling force on the body. The body must be able to generate heat, retain heat,
and discharge heat depending on the body activity and ambient external
2. Body temperature is a measure of
the metabolism - the general level of chemical activity within the body.
3. The hypothalamus is the major
center of the brain for regulating body temperature. It is sensitive to blood
temperature changes of as little as 0.5 degrees Celsius and also reacts to nerve
impulses received from nerve endings in the skin.
4. The optimum temperature for
chemical reactions to take place in the body is 98.6 degrees F. Above 105 F many
body enzymes become denatured and chemical reactions cannot take place leading
to death. Below 98.6 F chemical reactions slow down with various complications
which can lead to death.
5. Core = the internal body organs,
particularly the heart, lungs, and brain.
Periphery = the appendages, skin, and muscle tissue.
6. Core temperature is the
temperature that is essential to the overall metabolic rate of the body.
The temperature of the periphery is not critical.
How Your Body
Regulates Core Temperature
1. Vasodilation - increases surface
blood flow, increases heat loss (when ambient temperature is less that body
temperature). Maximal vasodilation can increase cutaneous blood flow to 3000
ml/minute (average flow is 300-500 ml/minute).
2. Vasoconstriction - decreases
blood flow to periphery, decreases heat loss. Maximal vasoconstriction can
decrease cutaneous blood flow to 30 ml/minute.
3. Sweating - cools body through
4. Shivering - generates heat
through increase in chemical reactions required for muscle activity. Visible
shivering can maximally increase surface heat production by 500%. However, this
is limited to a few hours because of depletion of muscle glucose and the onset
5. Increasing/Decreasing Activity
will cause corresponding increases in heat production and decreases in heat
6. Behavioral Responses - putting
on or taking off layers of clothing will result in heat regulation
1. Hypothermia - "a decrease
in the core body temperature to a level at which normal muscular and cerebral
functions are impaired."
2. Conditions Leading to
- Cold temperatures
- Improper clothing and equipment
- Fatigue, exhaustion
- Poor food intake
- No knowledge of hypothermia
- Alcohol intake - causes
vasodilation leading to increased heat loss
3. What are "hypothermia"
- Below freezing
- 40 degrees - Ex. Shenandoahs,
wind and rain
- 60 degrees - Ex. Rayanna and
- Any temperature less than 98.6
degrees can be linked to hypothermia (ex. hypothermia in the elderly in cold
houses) or peripheral circulation problems such as trench foot and
4. Signs and Symptoms of
a. Watch for the "Umbles"
- stumbles, mumbles, fumbles, and grumbles which show changes in motor
coordination and levels of consciousness.
b. Mild Hypothermia - core
temperature 98.6 - 96 degrees F
- Shivering - not under voluntary
- Can't do complex motor functions
(ice climbing or skiing) can still walk & talk
- Vasoconstriction to periphery
c. Moderate Hypothermia - core
temperature 95 - 93 degrees F
- Dazed consciousness
- Loss of fine motor coordination
- particularly in hands - can't zip up parka, due to restricted peripheral
- Slurred speech
- Violent shivering
- Irrational behavior -
Paradoxical Undressing - person starts to take off clothing, unaware s/he is
- "I don't care
attitude" - flattened affect
d. Severe Hypothermia - core
temperature 92 - 86 degrees and below (immediately life threatening)
- Shivering occurs in waves,
violent then pause, pauses get longer until shivering finally ceases -
because the heat output from burning glycogen in the muscles is not
to counteract the continually dropping core temperature, the body shuts down
on shivering to conserve glucose
- Person falls to the ground,
can't walk, curls up into a fetal position to conserve heat
- Muscle rigidity develops -
because peripheral blood flow is reduced and due to lactic acid and CO2
buildup in the muscles
- Skin is pale
- Pupils dilate
- Pulse rate decreases
- at 90 degrees the body tries to
move into hibernation, shutting down all peripheral blood flow and reducing
breathing rate and heart rate.
- at 86 degrees the body is in a
state of "metabolic icebox." The person looks dead but is still
e. Death from Hypothermia
- Breathing becomes erratic and
- Cardiac arrythmias develop, any
sudden shock may set off Ventricular Fibrillation
- Heart stops, death
5. How to Assess if someone is
- If shivering can be stopped
voluntarily = mild hypothermia
- Ask the person a question that
requires higher reasoning in the brain (count backwards from 100 by 9's). If
the person is hypothermic, they won't be able to do it. [Note: there are
also other conditions such as altitude sickness that can also cause the same
- If shivering cannot be stopped
voluntarily = moderate - severe hypothermia
- If you can't get a radial pulse
at the wrist it indicates a core temp below 90 - 86 degrees
- The person may be curled up in a
fetal position. Try to open their arm up from the fetal position, if it
curls back up, the person is alive. Dead muscles won't contract only live
shivering can begin
sensation, goose bumps, unable to perform complex tasks with hands,
shiver can be mild to severe, hands numb
||95º - 93ºF
||Shivering, intense, muscle
incoordination becomes apparent, movements slow and labored, stumbling
pace, mild confusion, may appear alert. Use sobriety test, if unable
to walk a 30 foot straight line, the person is hypothermic.
|93º - 90ºF
persists, difficulty speaking, sluggish thinking, amnesia starts to
appear, gross muscle movements sluggish, unable to use hands, stumbles
frequently, difficulty speaking, signs of depression, withdrawn.
stops, exposed skin blue of puffy, muscle coordination very poor,
inability to walk, confusion, incoherent/irrational behavior, but may
be able to maintain posture and appearance of awareness
rigidity, semiconscious, stupor, loss of awareness of others, pulse
and respiration rate decrease, possible heart fibrillation
heart beat and respiration erractic, pulse may not be palpable
edema, cardiac and respiratory failure,death. Death may occur before
this temperature is reached.
The basic principles of rewarming a
hypothermic victim are to conserve the heat they have and replace the body fuel
they are burning up to generate that heat. If a person is shivering, they have
the ability to rewarm themselves at a rate of 2 degrees C per hour.
Mild - Moderate
1. Reduce Heat Loss
- Additional layers of clothing
- Dry clothing
- Increased physical activity
2. Add Fuel & Fluids
It is essential to keep a
hypothermic person adequately hydrated and fueled.
a. Food types
- Carbohydrates - 5 calories/gram
- quickly released into blood stream for sudden brief heat surge - these are
the best to use for quick energy intake especially for mild cases of
- Proteins - 5 calories/gram -
slowly released - heat given off over a longer period
- Fats - 9 calories/gram - slowly
released but are good because they release heat over a long period, however,
it takes more energy to break fats down into glucose - also takes more water
to break down fats leading to increased fluid loss
b. Food intake
- Hot liquids - calories plus heat
- Sugars (kindling)
- GORP - has both carbohydrates
(sticks) and proteins/fats (logs)
c. Things to avoid
- Alcohol - a vasodilator -
increases peripheral heat loss
- Caffeine - a diuretic - causes
water loss increasing dehydration
- Tobacco/nicotine - a
vasoconstrictor, increases risk of frostbite
3. Add Heat
- Fire or other external heat
- Body to body contact. Get into a
sleeping back, in dry clothing with a normothermic person in lightweight dry
1. Reduce Heat Loss
- Hypothermia Wrap: The idea is to
provide a shell of total insulation for the patient. No matter how cold,
patients can still internally rewarm themselves much more efficiently than
any external rewarming. Make sure the patient is dry, and has a
polypropylene layer to minimize sweating on the skin. The person must be
protected from any moisture in the environment. Use multiple sleeping bags,
wool blankets, wool clothing, Ensolite pads to create a minimum of 4"
of insulation all the way around the patient, especially between the patient
and the ground. Include an aluminum "space" blanket to help
prevent radiant heat loss, and wrap the entire ensemble in plastic to
protect from wind and water. If someone is truly hypothermic, don't put
him/her naked in a sleeping bag with another person.
2. Add Fuel & Fluids
- Warm Sugar Water - for people in
severe hypothermia, the stomach has shut down and will not digest solid food
but can absorb water and sugars. Give a dilute mixture of warm water with
sugar every 15 minutes. Dilute Jello works best since it is part sugar
and part protein. This will be absorbed directly into the blood stream
providing the necessary calories to allow the person to rewarm themselves.
One box of Jello = 500 Kilocalories of heat energy. Do not give full
strength Jello even in liquid form, it is too concentrated and will not be
- Urination - people will have to
urinate from cold diuresis. Vasoconstriction creates greater volume pressure
in the blood stream. The kidneys pull off excess fluid to reduce the
pressure. A full bladder results in body heat being used to keep urine warm
rather than vital organs. Once the person has urinated, it precious body
heat will be used to maintain the temperature of vital organs. So in the end
urinating will help conserve heat. You will need to help the person urinate.
Open up the Hypothermia Wrap enough to do this and then cover them back up.
You will need to keep them hydrated with the dilute Jello solution described
3. Add Heat
Heat can be applied to transfer
heat to major arteries - at the neck for the carotid, at the armpits for the
brachial, at the groin for the femoral, at the palms of the hands for the
- Chemical heat packs such as the
Heat Wave provides 110 degrees F for 6-10 hours.
- Hot water bottles, warm rocks,
- For a severely hypothermic
person, rescue breathing can increase oxygen and provide internal heat.
Is a situation in which the core
temperature actually decreases during rewarming. This is caused by peripheral
vessels in the arms and legs dilating if they are rewarmed. This dilation sends
this very cold, stagnate blood from the periphery to the core further decreasing
core temperature which can lead to death. In addition, this blood also is very
acetic which may lead to cardiac arrythmias and death. Afterdrop can best be
avoided by not rewarming the periphery. Rewarm the core only! Do not expose a
severely hypothermic victim to extremes of heat.
CPR & Hypothermia
When a person is in severe
hypothermia they may demonstrate all the accepted clinical signs of death:
- Blue skin
- Fixed and dilated pupils
- No discernable pulse
- No discernable breathing
- Comatose & unresponsive to
- Rigid muscles
But they still may be alive in a
"metabolic icebox" and can be revived. You job as a rescuer is to
rewarm the person and do CPR if indicated. A hypothermia victim is never cold
and dead only warm and dead. During severe hypothermia the heart is
hyperexcitable and mechanical stimulation (such as CPR, moving them or
Afterdrop) may result in fibrillation leading to death. As a result CPR may be
contraindicated for some hypothermia situations:
1. Make sure you do a complete
assessment of heart rate before beginning CPR. Remember, the heart rate may be
2-3/minute and the breathing rate 1/30 seconds. Instituting cardiac compressions
at this point may lead to life-threatening arrythmias. Check the carotid pulse
for a longer time period (up to a minute) to ascertain if there is some slow
heartbeat. Also, even though the heart is beating very slowly, it is filling
completely and distributing blood fairly effectively. External cardiac
compressions only are 20-30% effective. Thus, with its severely decreased
demands, the body may be able to satisfy its circulatory needs with only 2-3
beats per minute. Be sure the pulse is absent before beginning CPR. You will
need to continue to do CPR as you rewarm the person.
2. Ventilation may have stopped but
respiration may continue - the oxygen demands for the body have been so
diminished with hypothermia that the body may be able to survive for some time
using only the oxygen that is already in the body. If ventilation has stopped,
artificial ventilation may be started to increase available oxygen. In addition,
blowing warm air into the persons lungs may assist in internal rewarming.
3. CPR Procedures
- Check radial pulse, between 91.4
and 86 degrees F this pulse disappears
- Check for carotid pulse - wait
at least a full minute to check for very slow heartbeat
- If pulse but not breathing or
slow breathing, give rescue breathing (also adds heat).
- If no discernible heartbeat
begin CPR and be prepared to continue - persons with hypothermia have been
given CPR for up to 3.5 hours and have recovered with no neurological damage
- Begin active rewarming
Tissue temperature in cold weather
is regulated by two factors, the external temperature and the internal heat
flow. All cold injuries described below are intimately connected with the degree
of peripheral circulation. As peripheral circulation is reduced to prevent heat
loss to the core these conditions are more likely to occur.
1. Factors influencing cold
- Low ambient temperature
- Wind chill - increases rate of
- Moisture - wet skin freezes at a
higher temp than dry
- Contact with metal or
supercooled liquids (white gas)
- Exposed skin
- Previous cold injuries
- Constricting garments
- Local pressure
- Cramped position
- Body type
- Women do better in cold than men
(greater subcutaneous body fat)
- Caloric intake
- Diabetes, some medications
- Caffeine, nicotine
2. Cold-induced Vasodilation - When
a hand or foot is cooled to 59 degrees F, maximal vasoconstriction and minimal
blood flow occur. If cooling continues to 50 degrees, vasoconstriction is
interrupted by periods of vasodilation with an increase in blood and heat flow.
This "hunting" response recurs in 5-10 minute cycles to provide some
protection from cold. Prolonged, repeated exposure increases this response and
offers some degree of acclimatization. Ex. Eskimos have a strong response with
short intervals in between.
3. Pathophysiology of Tissue
Freezing - As tissue begins to freeze, ice crystals are formed within the cells.
As intracellular fluids freeze, extracellular fluid enters the cell and there is
an increase in the levels of extracellular salts due to the water transfer.
Cells may rupture due to the increased water and/or from tearing by the ice
crystals. Do not rub tissue; it causes cell tearing from the ice crystals. As
the ice melts there is an influx of salts into the tissue further damaging the
cell membranes. Cell destruction results in tissue death and loss of tissue.
Tissue can't freeze if the temperature is above 32 degrees F. It has to be below
28 degrees F because of the salt content in body fluids. Distal areas of the
body and areas with a high surface to volume ratio are the most susceptible (e.g
ears, nose, fingers and toes - this little rhyme should help remind you what to
watch out for in yourself and others).
- Surface frostbite generally
involves destruction of skin layers resulting in blistering and minor tissue
loss. Blisters are formed from the cellular fluid released when cells
- Deep frostbite can involve
muscle and bone
||May have sensation
4. Cold Response
- Circulation is reduce to the are
to prevent heat loss.
- The area may be pale, cold.
- It may have sensation or be
- Freezing of top layers of skin
- It is generally reversible
- White, waxy skin, top layer
feels hard, rubbery but deeper tissue is still soft
- Most typically seen on cheeks,
earlobes, fingers, and toes
- Rewarm the area gently,
generally by blowing warm air on it or placing the area against a warm body
part (partner's stomach or armpit)
- Do not rub the area - this can
damage the effected tissue by having ice crystals tear the cell
- Skin is white and
"wooden" feel all the way through
- Superficial frostbite includes
all layers of skin
- Numbness, possible anesthesia
- Deep frostbite can include
freezing of muscle and/or bone, it is very difficult to rewarm the appendage
without some damage occurring
- Superficial frostbite may be
rewarmed as frostnip if only a small area is involved
- If deep frostbite, see below for
7. Rewarming of Frostbite
- Rewarming is accomplished by
immersion of the effected part into a water bath of 105 - 110 degrees F. No
hotter or additional damage will result. This is the temperature which is
warm to your skin. Monitor the temperature carefully with a thermometer.
Remove constricting clothing. Place the appendage in the water and continue
to monitor the water temperature. This temperature will drop so that
additional warm water will need to be added to maintain the 105 - 110
degrees. Do not add this warm water directly to the injury. The water will
need to be circulated fairly constantly to maintain even temperature. The
effected appendage should be immersed for 25 - 40 minutes. Thawing is
complete when the part is pliable and color and sensation has returned. Once
the area is rewarmed, there can be significant pain. Discontinue the warm
water bath when thawing is complete.
- Do not use dry heat to rewarm.
It cannot be effectively maintained at 105 - 110 degrees and can cause burns
further damaging the tissues.
- Once rewarming is complete the
injured area should be wrapped in sterile gauze and protected from movement
and further cold.
- Once a body part has been
rewarmed it cannot be used for anything. Also it is essential that the part
can be kept from refreezing. Refreezing after rewarming causes extensive
tissue damage and may result in loss of tissue. If you cannot guarantee that
the tissue will stay warm, do not rewarm it. Mountaineers have walked out on
frozen feet to have them rewarmed after getting out with no tissue loss.
Once the tissue is frozen the major harm has been done. Keeping it frozen
will not cause significant additional damage.
8. Special Considerations for
- If the person is hypothermic and
frostbitten, the first concern is core rewarming. Do not rewarm the
frostbitten areas until the core temp approaches 96 degrees.
- No alcohol - vasodilation may
increase fluid buildup
- No smoking - nicotine as a
vasoconstrictor may increase chances for developing frostbite
- Liquids such as white gas can
"supercool" in the winter (drop below their freezing point but not
freeze). White gas also evaporates quickly into the air. Spilling
supercooled white gas on exposed skin leads to instant frostbite from
evaporative cooling. Always were gloves when handling fuel.
- Touching metal with bare skin
can cause the moisture on your skin to freeze to the metal. (In really cold
conditions, metal glasses frames can be a problem). When you pull away, you
may leave a layer of skin behind. Don't touch metal with bare skin.
9. Trench Foot - Immersion Foot
Trench foot is a process similar to
chilblains. It is caused by prolonged exposure of the feet to cool, wet
conditions. This can occur at temperatures as high as 60 degrees F if the feet
are constantly wet. This can happen with wet feet in winter conditions or wet
feet in much warmed conditions (ex. sea kayaking). The mechanism of injury is as
follows: wet feet lose heat 25x faster than dry, therefore the body uses
vasoconstriction to shut down peripheral circulation in the foot to prevent heat
loss. Skin tissue begins to die because of lack of oxygen and nutrients and due
to buildup of toxic products. The skin is initially reddened with numbness,
tingling pain, and itching then becomes pale and mottled and finally dark
purple, gray or blue. The effected tissue generally dies and sluffs off. In
severe cases trench foot can involve the toes, heels, or the entire foot. If
circulation is impaired for > 6 hours there will be permanent damage to
tissue. If circulation is impaired for > 24 hours the victim may lose the
entire foot. Trench Foot causes permanent damage to the circulatory system
making the person more prone to cold related injuries in that area. A similar
phenomenon can occur when hands are kept wet for long periods of time such as
kayaking with wet gloves or pogies. The damage to the circulatory system is
known as Reynaud's Phenomenon.
Treatment and Prevention of Trench
- Includes careful washing and
drying of the feet, gentle rewarming and slight elevation. Since the tissue
is not frozen as in severe frostbite it is more susceptible to damage by
walking on it. Cases of trench foot should not walk out; they should be
evacuated by litter. Pain and itching are common complaints. Give Ibuprofen
or other pain medication.
- Prevention is the best approach
to dealing with trench foot. Keep feet dry by wearing appropriate footwear.
Check your feet regularly to see if they are wet. If your feet get wet
(through sweating or immersion), stop and dry your feet and put on dry
socks. Periodic air drying, elevation, and massage will also help. Change
socks at least once a day and do not sleep with wet socks. Be careful of
tight socks which can further impair peripheral circulation. Foot powder
with aluminum hydroxide can help. High altitude mountaineers will put
antiperspirant on their feet for a week before the trip. The active
ingredient, aluminum hydroxide will keep your feet from sweating for up to a
month and their are no confirmed contraindications for wearing
antiperspirant. [Some studies have shown links between aluminum in the body
and Alzheimer's.] Vapor barrier socks may increase the possibility of trench foot.
When you are active and you are wearing a vapor barrier sock, you must
carefully monitor how you sweat. If you are someone who sweats a lot with
activity, your foot and polypropylene liner sock may be totally soaked
before the body shuts down sweating. Having this liquid water next to the
skin is going to lead to increased heat loss. If you dont sweat much,
your body may shut down perspiration at the foot before it gets actually
wet. This is when the vapor barrier system is working. You must experiment
to determine if vapor barrier systems will work for you.
- Caused by repeated exposure of
bare skin to temperatures below 60 degrees
- Redness and itching of the
- Particularly found on cheeks and
ears, fingers and toes
- Women and young children are the
- The cold exposure causes damage
to the peripheral capillary beds, this damage is permanent and the redness
and itching will return with exposure
11. Avoiding Frostbite and Cold
- "Buddy system" - keep
a regular watch on each other's faces, cheeks, ears for signs of
- Keep a regular "self
check" for cold areas, wet feet, numbness or anesthesia
- If at any time you discover a
cold injury, stop and rewarm the area (unless doing so places you at greater
12. Eye Injuries
a. Freezing of Cornea
- Caused by forcing the eyes open
during strong winds without goggles
- Treatment is very controlled,
rapid rewarming e.g. placing a warm hand or compress over the closed eye.
After rewarming the eyes must be completely covered with patches for 24 - 48
b. Eyelashes freezing together
- Put hand over eye until ice
melts, then can open the eye
- Sunburn of the eyes
- Prevention by wearing good
sunglasses with side shields or goggles. Eye protection from sun is just as
necessary on cloudy or overcast days as it is in full sunlight when you are
on snow. Snow
blindness can even occur during a snow storm if the cloud cover is thin.
- Occur 8-12 hours after exposure
- Eyes feel dry and irritated,
then feel as if they are full of sand, moving or blinking becomes extremely
painful, exposure to light hurts the eyes, eyelids may swell, eye redness,
- Cold compresses and dark
- Do not rub eyes
to Rick Curtis for the majority of the above information.
Have You Learned About Hypothermia?
weather can affect older adults because many take medications that can interfere
with the body's ability to regulate
makes your body lose heat.
and slow, slurred speech are symptoms of
4. The best
way to find out if someone is suffering from hypothermia is to use a
5. If you
suspect hypothermia and emergency aid is not available right away, move the
person to a warmer location and wrap them in a warm blanket to stop heat
Hypothermia affects younger people more often than older
7. Rubbing a
hypothermia victim's arms and legs will
illnesses place people at risk because they affect the way the body handles cold
9. Wind chill
plays no role in hypothermia.
10. Hot meals
may prevent hypothermia.