Archive for the ‘Hypothermia’ Category

Book Review:

March 22, 2007

Hypothermia, Frostbite, and other Cold Injuries
Prevention, Survival, Rescue, and Treatment

By Gordon Giesbrecth, Ph.D., and James A. Wilkerson, M.D.

The book is published by The Mountaineers Books
They describe themselves as “Outdoor books by the experts” and in this case it is certainly true. The authors of this text are recognized experts in the field of cold-related injuries.

The authors have done an excellent job of describing and reviewing the various cold-related injuries. The text is up-to-date, comprehensive, well written, and applicable. This is a very useful body of knowledge for both the outdoor enthusiast as well as mountain rescue personnel. The authors have taken the time to provide information on the fundamentals of thermoregulation and clothing design as well as the recognition and management of cold-related injuries. I had the opportunity and honor of writing the chapter on non-freezing cold injuries.

If you enjoy the outdoors, or if you are a provider wilderness emergency medicine and rescue, this is a must read book. I think you will enjoy it.

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Free Sample Issue of the Wilderness Medicine Newsletter

March 12, 2007

Due to the popularity of the Frozen Mythbusters series on this site, we have decided to make the entire original article by Gordon Giesbrecht, PhD; Murray Hamlet, DVM; and Frank Hubbell, DO,from the Wilderness Medicine Newsletter available as a free pdf file.

Click here to download Volume 15, Number 6, of the Wilderness Medicine Newsletter; “Frozen Mythbusters”.

Please note this is a large file and, depending on your computer, may take several minutes to download.

This blog is powered by the Wilderness Medicine Newsletter, now celebrating 20 years of publication. The WMN is published and distributed online six times each year by TMC Books, and subscriptions cost as little as $10 per year. To find out more, or to subscribe online, click here.

Heat Loss Through the Head and Hypothermia

February 14, 2007

The rate of heat loss, at rest, with exercise, and with hypothermia

Since there has been a fair amount of interest regarding Myth #2 in the Wilderness Medicine Newsletter – Frozen Mythbusters, Nov/Dec 2004 – the topic deserves more discussion.

MYTH #2 states.  “If your feet are cold, cover your head because you can lose up to 75% of your body heat through your head alone.

The problem is that the head is only about 10% of the body surface area.  Thus, the head would have to lose about 40 times as much heat per square inch or centimeter compared to the rest of the body.
 
Gordon had heard this statement one too many times and finally decided to see if this was indeed true.  So he took several test subjects, all volunteers, of course, (you have to wonder what problem they caused at the university), wired them to monitor their core temperatures, and discovered that we do indeed lose heat through any exposed part of the body and the amount of heat we lose depends on the amount of exposed surface area.  The rate of heat loss is relatively the same for any exposed part of the body not simply the head. You do not lose heat significantly faster through the scalp than any other portion of the body with the same surface area. 

It is still a good idea to put on a hat (a hood really – what insulation does a baseball hat have?) if your feet are cold.  But what is BUSTED is that there is nothing peculiar or unique about the head. The idea that we lose heat faster through out scalp, because of the constant blood supply to the brain, is simply a myth. (One that I personally have believed for many years.)”

UPDATE & DISCUSSION
 
#1 Heat loss via the head at rest, during exercise, and with hypothermia:

I did have the opportunity to speak with Dr. Murray Hamlet about this topic, and we hope this additional information will help to clarify heat loss in the hypothermia patient.

The cerebral blood flow is supplied via the carotid and vertebral arteries (4 in total) and is constant. The blood flow to the brain does not change as the demand for oxygen is constant. As a result, when you look at total heat loss, the head accounts for about 7% of the heat lost. 

The cerebral blood flow does, however, vary based on cardiac output – the harder your heart beats, the greater the blood flow to the brain.  And as you increase the blood flow to the brain, you also increase the percentage of heat loss.  As it turns out, when you begin to exercise, there is increased cerebral blood flow. This increases the percentage of heat lost through the head to about 50% of total body heat loss.  But as the person continues to exercise, the muscles demand more oxygen which increases blood flow. To ensure thermoregulation and maintain normal core temperature (exercises increases body heat), the skin vasodilates which increases blood flow to the skin to cool the blood. The net result is a decrease in the total blood flow to the brain and a decrease in percentage of total body heat lost through the head to about 10%.  Once sweating begins, the percent lost through the scalp returns to 7%.

In Gordon’s research his test subjects were at rest in cool water, and the researchers were comparing the rate of heat lost by monitoring core temperature through different body parts and quantities of skin exposed.  At rest, they found that the rate of heat loss only depended upon the amount of skin surface area exposed, and the percentage of heat lost through the head was the same as the rest of the body.

Research at the Army Research in Environmental Medicine labs showed that there was a temporary increase in heat loss through the scalp that returned to the baseline of 7% as the subjects continued to exercise.

Now, what about hypothermia and heat loss through the head? 
If the hypothermia victim is not shivering, they are at rest, and the heat loss through the head remains about 7%.  But, this is important, if they are shivering, the percent of heat loss via the scalp can increase to upwards of 55%, so protecting the head well is a very important part of treating the hypothermia patient.  And as you can imagine, the primary defense against the cold and hypothermia is vasoconstriction of the peripheral circulation, this shunts blood to the core, reduces circulation to the skin, and increases the percent of heat loss through the scalp.

The difference is that the shivering hypothermia patient is indeed exercising, but they do not vasodilate the peripheral circulation; the shivering muscles increase metabolic demand and cardiac demand so the patients do increase their cardiac output; therefore, they do increase cerebral circulation; therefore, they do increase the percent of blood loss through their head.

Treatment of the hypothermia victim:
Remove from the cold.
Get them dry and keep them dry.
Insulate from the ground.
Hypothermia wrap:
Re-insulate with dry insulation.
Cover and protect the head from further heat loss.
Cover and protect the hands and feet from frostbite.
 Surround with a windproof and waterproof layer.
If conscious, feed warm, sweet liquids.
If unconscious, evacuate and handle very gently to prevent ventricular fibrillation.

#2 How does being in water change the equation?

Life-preserver, personal flotation device (PFD), research has shown that when in the water, if your head and neck are wet, you cool faster.  This is why modern PFD’s hold the person in the water with their head and neck out of the water; even if unconscious, to decrease the rate of heat loss into the water.

#3 What difference does hair on your head or facial hair make?

None. 
In order for hair or fur to provide a protective thermal barrier, it has to be much denser than what we humans grow and it has to be in layers of different types of fur to provide a thermal barrier.  Beards are great, but they do not keep you any warmer. And bald is beautiful.

We at the Wilderness Medicine Newsletter appreciate the comments and discussion.
 

Hypothermia & Paradoxical Undressing

February 7, 2007

Hypothermia & Paradoxical Undressing

Recently in the news, there was a tragic event where a family got caught out in deep snow while driving through the mountains. Eventually, the father decided to leave his family in their car and go for help on foot. Unfortunately, through his valient effort, he didn’t survive that cold, harsh winter environment, and died of hypothermia. 

One of the discussions in the news was that even though he succumbed to the cold and hypothermia, at some point he had taken off some of his clothes. This is a phenomenom associated with hypothermia known as paradoxical undressing.

Pathophysiology:
The supposition as to the cause of paradoxical undressing is that the primary defense against the cold and hypothermia is vasoconstriction of the peripheral circulation. This shunts the blood into the warm core and the skin now becomes a more effective layer of insulation. The problem is that vasoconstriction of the smooth muscles in the vasculature requires glucose and energy consumption. Vasodilation, on the other hand, is a passive process that simply requires the smooth muscles that make up the blood vessels to relax. Over time, the vasoconstricted vessels begin to run out of energy (glucose) because of the poor circulation, and they fatigue and relax, thus vasodilating. This now allows the warm core-blood to re-perfuse the skin, causing a sensation of warmth. This results in the hypothermia victim feeling warm, so, they now begin to shed layers, thus the paradoxical undressing. Between the peripheral vasodilation and the loss of layers of protective clothing, their core temperature now begins to plummet and this hastens death from hypothermia.

I spoke with Dr. Murray Hamlet about parodoxical undressing and hypothermia and his experience and expertise with this phenomenom is the same as ours, in that we do not know of any cases where a hypothermia victim that underwent paradoxical undressing survived.

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Cold-Related Injuries #10 Hospital Management of Hypothermia

December 16, 2006

1.  Recognize Hypothermia:
Use low-reading thermometers and use esophageal thermometer to monitor core temperature.

2.  Airway: 
Obtain a patent airway and ventilate. 
Beware – using heated, moist air will suppress the shivering mechanism.
Shivering is the most efficient way to rewarm.

3.  ECG and continuous cardiac monitoring:

4.  Monitor Labs:
CBC, electrolytes, glucose, ABG (do not adjust for temperature)

5.  Initiate rewarming:
Shell: if > 30°C, maintain blood sugar to encourage shivering, peripheral rewarming.
Core: if < 30°C and unconscious, arteriovenous fistula and body cavity lavage.
In cardiac arrest, cardiopulmonary bypass is preferred for rewarming.

6.  Warning:
Low core temperature potentiates the fibrillatory effect of elevated K and a low pH.

An excellent reference is:
Chapter 58, Hypothermia and Hyperthermia, Clinical Critical Care Medicine, Albert, et. al., published by Mosby 2006.

This blog is powered by the Wilderness Medicine Newsletter, now celebrating 20 years of publication. The WMN is published and distributed online six times each year by TMC Books, and subscriptions cost as little as $10 per year. To find out more, or to subscribe online, click here.

Cold-Related Injuries #9 Hypothermia – The Alligators

December 14, 2006

Alligators:
Like alligators, these are some of the problems that seem to sneak up and bite you when you least expect them.

1.  Not recognizing cold, stiff, cyanotic patient as resuscitatable.
The unconscious hypothermia victim, <86°F, has stopped shivering and is in a state of suspended animation (not hibernation). 
They appear breathless – a slow, shallow breath every 10 – 15 seconds.
They appear pulseless; at <90°F the blood is 190% thicker than usual, therefore, the pulse is not palpable, and the heart valves are not slamming shut, so no heart sounds.
The skin is very cool, pale gray or cyanotic, and firm to the touch.
If alive, they are curled up in the fetal position. 
When they die, they tend to extend their limbs and may have vomitus in or around their mouth.
If alive, when you gently pull on an arm, it will extend out; when released, it will flex back against the body.  It takes life to contract a muscle.

2.  Field use of CPR on a functional heart.
If possible, attach to a cardiac monitor. If flatline, they are in arrest.
If they have a cardiac rhythm, they are not in PEA – you just can’t feel the weak pulse.

3.  Criteria for pronouncing dead:
No palpable pulse and ECG is flat line.
No respirations.
Skin color is pale gray, cyanotic, and cold.
They have rigidity.
Pupils are fixed.
Failure to revive after rewarming –  “Not dead until warm and dead.”

4.  Continuing active rewarming past 32°C with a high K and a low pH.
Remember, hypothermia is not a disease.  Take your time.
These folks have normal physiology for that temperature.  With rewarming, the cells hve to have time to adjust the chemistry and move the K back into the cells.

5.  Using too many drugs when cold; anti-arrhythmics, calcium channel blockers.
We do not know how drugs affect the body at subnormal core temperatures, this has never been studied.  Hypothermics have poor peripheral circulation.  Drugs end up pooling in the peripheral circulation. With rewarming, the peripheral circulation is re-established. The drugs will flood into the system with potentially disasterous consequences, i.e. post rewarming overdose.

6.  Confusing immersion with submersion.
Immersion
– When immersed, the airway does not go below the surface of the water.
This is shell hypothermia not drowning, and patients are easily resuscitated.
Submersion – their airway went below the surface; they have drowned, have core hypothermia, and are harder to resuscitate.

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Cold-Related Injuries #8 – Treatment of Hypothermia

December 12, 2006

STAGES OF HYPOTHERMIA:

98.6F – Normal
97F – Brain fails; judgment fails; protective and survival instincts fade.
96F – Shivering begins as a constant (uncontrollable) fine motor tremor.
94F – Shivering increases, coordination fails, tripping and falling begin.
92F – Shivering becomes intense; patient is unable to walk.
90F – Shivering becomes convulsive, fetal position is adopted; patient is unable to talk.
86F & below – “Metabolic Icebox”:  unconscious, ashen gray, may appear pulseless/breathless.

TREATMENT:   

Remove from immediate danger and further exposure.
GET DRY & KEEP DRY. Insulate with hypothermia wrap.
Give warm, sweet liquids – Jell-O if conscious.

Click on the image below to see a hypothermia wrap.

hypo-wrap-for-blog.gif

The Hypothermia Wrap – “The Human Burrito”

Remove wet or damp clothing.
Insulate with multiple layers of dry material, clothing, blankets, sleeping bags.
Cover and insulate their head with a warm hat.
Super-insulate their feet and add chemical heat packs if you have them.
Insulate from the ground with ensolate pads.
Surround with a windproof & waterproof layer.

PREVENTION: 

Know your enemy: 
Be prepared for wet, wind, and cold.
Wear fabrics that stay warm when wet (NO COTTON!).
Stay dry. Stay well HYDRATED.
Snack often on quick-burning carbohydrates – sugar.
Carry bivouac gear and know how to use it.
Be attentive to yourself, to your companions, and to the environment.
Do not tolerate the cold or cold extremities.
React early & quickly.

For more detailed information on Hypothermia see the Jan/Feb 2004 issue, When Jack Frost Bites, and the Nov/Dec 2004 issue, Frozen Mythbusters, of the Wilderness Medicine Newsletter. Click on this link to learn more about or subscribe to the Wilderness Medicine Newsletter.

This blog is powered by the Wilderness Medicine Newsletter, now celebrating 20 years of publication. The WMN is published and distributed online six times each year by TMC Books, and subscriptions cost as little as $10 per year. To find out more, or to subscribe online, click here.

Cold-Related Injuries #7 – Hypothermia

December 10, 2006

HYPOTHERMIA

Hypothermia is a lowering of body’s core temperature to level where normal brain & muscle function are impaired.
It is the one of the most common threats and causes of wilderness emergencies.
We are a hairless mammal, designed for the hot tropics, not the cold environs.
We have little or no defense against the cold, other than behavior, i.e., wear warm clothing.

THERMOREGULATION:
Balance of heat production & heat loss.
Thermoequilibrium is monitored & controlled by the brain.
Thermoregulation is performed by the skin, via the vasculature.

Heat Production: 
Internal sources:
Basal metabolism – burning of glucose to produce heat
Nutrition/digestion – “logs on the fire”
Exercise/shivering – muscle contraction to produce heat (as byproduct)
External sources:
Fire, stoves, sun, other people

Heat Loss:         
Conduction – heat transfer from one solid object to another
Convection – heat transfer from solid object to air
Radiation – infrared energy given off by warm objects      
Evaporation – heat transfer to water during liquid to gas change

Body’s defensive reaction to cooling off: 

NO WARNING OF IMPENDING DOOM
Peripheral vasoconstriction
– skin’s attempt to decrease heat loss.
Involuntary shivering – muscles’ attempt to produce heat.
Increased basal metabolism – may increase to 5 times its normal rate.

For more detailed information on Hypothermia see the Jan/Feb 2004 issue, When Jack Frost Bites, and the Nov/Dec 2004 issue, Frozen Mythbusters, of the Wilderness Medicine Newsletter. Click on this link to learn more about or subscribe to the Wilderness Medicine Newsletter.

This blog is powered by the Wilderness Medicine Newsletter, now celebrating 20 years of publication. The WMN is published and distributed online six times each year by TMC Books, and subscriptions cost as little as $10 per year. To find out more, or to subscribe online, click here.

Cold-Related Injuries #6 – Raynaud’s Disease

December 8, 2006

Raynaud’s Disease:

This is also a non-freezing cold injury. 
It is a hypersensitivity reaction to cold exposure.
It is more of a nuisance than a limb-threatening injury.
This condition has been caused by chronic cold exposure and, for some unknown reason, the peripheral circulation has now developed an exaggerated response to the cold which now occurs at warmer temperatures, i.e., not as cold as it used to have to be.  The peripheral circulation in the hands and/or feet will now overreact and vasoconstrict or close down too much.
So, the response is too early and too much.
Upon rewarming, there is also an exaggerated response: the skin will turn red, and painful.  The extremity may also throb with pain during the rewarming process.
Once rewarmed the tissues should return to normal.

Treatment of Raynaud’s:

Avoid and limit cold exposure.
Keep the affected areas well-insulated, warm, and dry.
Avoid nicotine, caffeine, alcohol, and over-the-counter decongestants.
Drugs:  may try calcium channel blockers for their vasodilatory effects.
 Eg:  Nifedine XL 30 – 90mg po qd, or diltiazem 30 – 120mg po qid.
“Pavlovian” response trials, also known as Murray’s Method (for Dr. Murray Hamlet),  a technique to re-educate the nerves affecting the vasculature.

Rehabbing Raynaud’s or Murray’s Method:

Equipment: 2 – 4 Styrofoam coolers, 2 for hands + 2 for feet.
Warm water.
Warm inside & cool, <32°F (0°C) outside.
Fill the Styrofoam coolers with warm water, 105°F – 110°F, one set inside and one set outside.
Start inside, dressed lightly so that you are comfortable, and sit with your hands or feet in the warm water for about 5 mintues; then, get up and go outside.  Stay lightly dressed, and put your hands or feet in the warm water outside, for 5 – 10 minutes. 
For this to work your body has to be able to cool off while your hands and feet stay warm.  This is the re-education process.
You have to repeat this process about 50 times.  It seems to be most effective when you do this about 5 times a day, every other day.

Click on the images below to see full size.

raynauds-2-for-blog.gif   raynauds-1-for-blog.gif

For more detailed information on Raynaud’s Disease see the Jan/Feb 2005 issue of the Wilderness Medicine Newsletter, Non-Freezing Cold Injuries.  Click on this link to learn more about or subscribe to the Wilderness Medicine Newsletter.

This blog is powered by the Wilderness Medicine Newsletter, now celebrating 20 years of publication. The WMN is published and distributed online six times each year by TMC Books, and subscriptions cost as little as $10 per year. To find out more, or to subscribe online, click here.

Cold-Related Injuries #5 – Trenchfoot/Immersion Foot

December 6, 2006

TRENCHFOOT/IMMERSION FOOT

A non-freezing cold injury that is caused by continual dampness and cold of the hands or feet.
The wet and cold causes vasoconstriction of the peripheral circulation in the hands or feet reducing blood flow, causing ischemia. 
The skin can survive with reduced circulation for about 6 hours; after that it will die from ischemia. 
The resulting injury is severe, painful, and lifelong.

Cause: 
Vasoconstriction deprives hands or feet of adequate blood supply for too long.

Symptoms:
While wet and cold: 
The extremities are cold, wet, numb, and macerated (wrinkled from being waterlogged).  
With rewarming: 
The extremities become red, swollen, painful; may lead to gangrene or nerve damage.

Treatment:  TREAT THE WHOLE PATIENT
Remove all wet clothing.
Get them dry & Keep them dry.
Reinsulate  & Rewarm.
Hydrate & Feed with sickly sweet drinks – warm liquid Jello is best because it has lots of calories.
Do not allow them to get cold and wet again.
NSAID’s;  eg. ibuprofen 800mg po tid, may be given with Tylenol for pain relief.
Evacuate.

PREVENTION:
Keep hands and feet dry.
Change socks regularly.
Sleep in dry socks at night.
Make sure foot gear is not too tight, impairing circulation.
Do not tolerate cold, numb, wet extremities – Do something!

For more detailed information of trench/immersion foot injuries see the Jan/Feb 2005 issue of the Wilderness Medicine Newsletter, Non-Freezing Cold Injuries.  Click on this link to learn more about or subscribe to the Wilderness Medicine Newsletter.

This blog is powered by the Wilderness Medicine Newsletter, now celebrating 20 years of publication. The WMN is published and distributed online six times each year by TMC Books, and subscriptions cost as little as $10 per year. To find out more, or to subscribe online, click here.