Archive for the ‘Cold injuries’ Category

New! From The Wilderness Medicine Newsletter

February 10, 2012

For decades the Wilderness Medicine Newsletter has provided up-to-date information to pre-hospital and definitive care providers. Since becoming an on-line journal, the readership of the WMN has become international. Now the WMN has it’s own web site: www.wildernessmedicinenewsletter.com

Subscribers pay the same $15 a year subscription rate but have access to more than 165 articles from back issues as well as current issues. You can search the site either by category, or by key words making the Wilderness Medicine Newsletter site a much more useful reference for everything from reviewing splinting to the prevention and treatment of tropical diseases.

Check it out!

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Wilderness Medicine by Paul S. Auerbach, MD, MS

April 9, 2007

Once again, Paul Auerbach has managed to provide us with a tome that holds an absolute wealth of information. He has not only updated all the information contained in the previous edition, but he has also called upon more experts in the field who have added a wide variety of new topics. The list of contributing authors reads like a Who’s Who in Wilderness Medicine and Rescue. This text is a true accomplishment and a marvelous contribution to the wild side of medicine.

The Fifth Edition, 2007, consisting of 2316 pages is divided into 97 chapters, written by 157 contributing authors. A myriad of charts, tables, and spectacular photography complement the well-written text.

Needless to say, I have not had the time to read the entire book, but the several chapters I have read were packed with valuable information for all of us who are interested in or participate in wilderness medicine and rescue work.

Paul, a personal thanks. Great job! What a tremendous contribution this text will make to emergency medicine that is practiced in the extended care environment.

Wilderness Medicine, Fifth Edition, by Paul S. Auerbach, MD, MS is published by Mosby, ISBN 978-0-323-03228-5 and available through www.elsevier.com and probably amazon.com.

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.

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.

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.