The Wilderness Emergency Medical Services InstituteCOLD RELATED DISORDERSby Jim HillWEMT (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.
CORE TEMP = HEAT INPUT - HEAT LOSS.
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.