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The Wilderness Emergency Medical Services Institute


by Jim Hill

WEMT (Wilderness EMT)

Our thanks to Jim Hill for this article.
We hope it is the first of many more to come.
- Bernie

As pre-hospital care providers operating within the urban EMS system, recognition of cold related injuries is often overlooked. Modern conveniences combined with shorter transfer times tend to shift our focus away from the precipitating factors that contribute to a patient entering a hypothermic condition.

As an aid to understanding cold related disorders, it is important to review the mechanics of temperature balance. Homeostasis is the system within our body that uses feed back to create a thermal balance. Relying primarily on the hypothalamus, located deep within the anterior portion of the brain as well as other external sensors, heat production and loss is maintained. Just as turning up the thermostat in your home results in your furnace coming on, altering the "set point" of your hypothalamus results in shivering. When your core temperature stabilizes, the chills subside.

A by-product of your basal metabolic rate is heat production. In order to keep your body from melting down, there must be subsequent heat loss. This heat loss occurs in the following ways. Heat is lost by conduction when we sit on a cold surface. Convection removes heat when the micro layer of warmed air surrounding the body is replaced with colder air (Forced convection resulting from wind). Heat is radiated away when photons of infrared light are given off by the body. Evaporation of water (sweating) causes great heat loss, much of it going unnoticed. Respiration; remember, lung tissue is quite delicate and operates only with air warmed to core temperature and humidified to 100%. Therefore, just breathing results in significant heat loss!

For purposes of this discussion, the body will be divided into two parts, the core (chest and abdomen) and the periphery (everything else). Via the vascular system, heat is continuously transferred between the two. Reacting to the stimuli of the hypothalamus, constriction or dilation of these vessels adjusts the supply of heated blood from the core to the periphery.


This concept of thermal regulation requires the EMT to maintain a position of pro-active thinking. The body will transfer to the periphery a tremendous amount of heat before the core will register a heat loss. This chilling effect is known as incipient hypothermia and will always require that amount of heat loss to be "made up" in order to return to a comfortable temperature.

Our bodies are amazing in that we are somewhat adaptable to adverse conditions. This adaptation causes changes in both our cellular metabolism and the cardiovascular system. Thus acclimatization to heat can occur within one to three weeks with full acclimatization taking up to eight weeks. However, other than the reverse of heat adaptation, there is little we can do to adapt physiologically to the cold. Our primary adaptation to the cold environment is through behavior, clothing, shelter, and diet. Our role as emergency care providers should be pro-active in applying "appropriate behavior". For example, fire scene rehabilitation services should consider preventing the behavior that leads to incipient hypothermia.

Another consideration to the body's ability to maintain normal temperatures are drugs and diseases. Obviously there are many drugs that affect our body's ability to maintain heat. However there are three that are commonly overlooked. The first is tobacco. Nicotine, which is a stimulant similar in many ways to amphetamines and cocaine, is a vasoconstrictor. When the body is attempting to send small bursts of heated blood to the extremities in order to prevent frostbite, (The Hunting Phenomenon) vasoconstriction inhibits the process. Alcohol reputedly causes peripheral vasodilatation that adds to a loss of core temperature. However the most significant effect of alcohol in the cold environment is that it makes you stupid! Countless errors in judgment have been linked to deaths due to hypothermia. And finally, aspirin, acetaminophen, and ibuprofen interfere with the normal function of the hypothalamus. When administered in the cold environment, it can result in the body's inability to shiver, which as we know, is the mechanism that creates heat.

Diseases such as asthma, diabetes and even past exposure to cold stress, pre-dispose patients to hypothermia. Remember, 80% of the diagnosis comes from a thorough H & P (History & Physical)!

Within the wilderness setting, it is understood that wilderness patients will ALWAYS present with a combination of three maladies (which we may want to coin as the wilderness triad.) . Given adequate exposure to a cold environment, all patients will be hypothermic, hypoglycemic, and hypovolemic. This common thread results because hypothermia is a condition, not a disease. It is simply a result of the formula, Core Temp. = heat input - heat loss. If your patient is lying on the ground, no matter what the ambient temperature, HE WILL EVENTUALLY BECOME HYPOTHERMIC! A decreased body temperature engenders an increased metabolic rate (shivering). Shivering requires more energy, thus depleting energy (hypoglycemia). And finally, because the body transfers heat from the periphery to the core, the body perceives an increase in fluid volume. This triggers fluid excretion within the kidneys (cold diuresis) which ultimately results in volume depletion (hypovolemia).

Looking specifically at the various cold disorders, there are three that are typically linked and viewed as minor situations. It could be expected that an EMT would only see these in a wilderness setting. Chilblain is the mildest form of cold exposure and is typically not a medical emergency. It is diagnosed by a small area of red or cyanotic, slightly swollen and sometimes scaling skin. Covering the area with a good, greasy skin cream is sometimes helpful. Other treatments include vasodilators such as Nifedipine, Procordia or Adalat.

Immersion Foot and Trench Foot are conditions that present much like frost bite; however, they occur at temperatures above freezing when the foot is continuously immersed in water. Trench foot differs from Immersion foot in that Trench foot is associated with trauma or poor circulation. The condition typically develops in three phases. First there are vasospasums and numbness. The second occurs after rewarming and presents with red, hot, painful blisters. The final phase is the healing phase which results in cold sensitivity. Both injuries are treated similar to frostbite and are prevented by keeping hydrated and maintaining dry feet.

The next consideration in cold related injuries are frost nip and frost bite. With frost nip, there is freezing of the superficial tissues commonly diagnosed by a blanching of fingers, noses, ears, etc. Frost bite, however, is significantly more serious. There we find freezing of the deep tissues resulting in the formation of ice crystals. Tissue damage occurs as we manipulate these crystals within the tissue (walking on the affected foot). Appropriate therapy is to rapidly rewarm the affected area. If available, provide Dextran IV , and PROTECT FROM REFREEZING.

Hypothermia is defined as an abnormally low body core temperature and is segmented into two categories Mild hypothermia = body temp to 90 degrees F. Severe hypothermia = body temp below 90 degrees F. Hypothermia is diagnosed by a low rectal or tympanic temp. Incipiently, it will present with ataxia, blank stares, slurred speech, shivering, mental or physical dysfunction. BE PRO-ACTIVE! Mild Hypothermia is a lot easier to manage than severe and mild hypothermia, left unchecked, WILL BECOME SEVERE!

When handling hypothermic patients, the word is GENTLE! Roughness, tilting and exertion can lead to inadequate cerebral circulation resulting in seizures, reflex vasodilation and ventricular fibrillation. All resulting in a really bad day for both you and your patient!!

Hypothermia is separated into various classifications and knowing the circumstances that precipitated it could have a bearing on the extent of treatment. Incipient, Primary, Secondary and Acute Hypothermia are all categories of hypothermia that are typically brought about by acute exposure. Treatment is similar and the outcome is usually good. However, a more difficult situation arises when your patient presents with an abnormally low core temperature, which is compounded by other medical and/ or non medical issues.

Subacute or Mountain hypothermia, Chronic Hypothermia, and Mixed Hypothermia are typically more complicated. They superimpose PMH's over the lower core temperature resulting in a condition that is much more difficult to manage.

As we enter this winter season, remember it's not a situation of will hypothermia present itself, ..... it is when will it present itself. Simple preventative measures include getting your patient off the ground ASAP! When assessing your patient, cover them up immediately after assessing that area. YOU, as the rescuer, prevent incipient hypothermia; dress accordingly, keep hydrated and maintain proper energy levels.

But most of all don't be stupid! Remember cold adaptation is primarily achieved through proper clothing, shelter and behavior.


Wilderness Emergency
 Medical Services Institute