|
Hypothermia
simply means lack of heat. For Search & Rescue members,
it is one of the primary enemies of a lost subject's unplanned
night out. Even moderate California temperatures such as
a 55 degree night can bring about hypothermias in any given
subject given the lack of shelter and a prolonged exposure.
As discussed in our "unexpected night out" training,
heat loss occurs in several ways:
-
Conduction
(heat transfers between objects in direct contact)
-
Convection
(similar to conduction, convection transfers heat via,
say, the layer of air between objects)
-
Radiation
(think of the sensation of heat loss off your face after
a day in the sun)
-
Evaporation
(heat exchange that occurs as water changes its state
from solid to liquid to gas)
-
Respiration
(as cold air is breathed into the lungs, it is warmed,
at the body’s expense)
|
Signs and symptoms of hypothermia are divided into
three categories. All temps are approximate.
|
| Mild
hypothermia |
| 96.8º
F. |
Pre-shivering
muscle tone |
| 95.0º
F. |
Uncontrolled
shivering (a physical strategy to generate heat) |
| 93.2º
F. |
Amnesia,
difficulty ambulating, and poor judgment |
| 91.4º
F. |
Ataxia
and apathy |
| Moderate
hypothermia |
| 89.6º
F. |
Stupor
(oxygen consumption decreases by 25 percent) |
| 87.8º
F. |
Shivering
ends |
| 86.0º
F. |
Atrial
fibrillation and other arrhythmias begin; cardiac
output is about 2/3rds of normal |
| 85.2º
F. |
Paradoxical
undressing; progressive decrease in level of consciousness,
pulse, and respiration; pupils dilate |
| 82.3º
F. |
Threshold
for ventricular fibrillation decreases; hypoventilation |
| 80.6º
F. |
Loss
of reflexes and voluntary motion |
| Severe
hypothermia |
| 78.8º
F. |
No
responses to pain or reflexes; acid-base disturbances
significant |
| 77.0º
F. |
Cerebral
blood flow 1/3rd of normal; cardiac output 45
percent of normal. Possibility of pulmonary edema |
| 75.2º
F. |
Significant
bradycardia and hypotension |
| 73.4º
F. |
Corneal
reflexes absent |
| 71.6º
F. |
Maximum
risk for ventricular fibrillation |
| 66.2º
F. |
EEG
silencing |
| 64.4º
F. |
Asystole |
| Source:
Paul S. Auerbach, ed., Wilderness Medicine,
3rd ed. (St. Louis: Mosby-Year Book, Inc., 1995),
p.55. |
|
If
one or more of these methods of heat loss exceeds the body’s
ability to stay warm, the core body temperature will fall.
SAR personnel should assume that
those being searched for are in need of assistance regardless
of the weather and other environmental circumstances.
Various factors
influence a person’s sensation of cold. Old age, lack of
activity, the influence of time of day (circadian rhythm),
alcohol and other drugs, and gender can all influence a
person’s ability to maintain body temperature.
Given that
most subjects are at risk when left outside overnight, the
SAR team’s primary task once finding a subject is to maintain
adequate body temperature by careful patient management.
Basically, keeping them warm by using the following strategies:
-
If the
patient is wet, remove wet garments and replace with
dry clothing, space blankets or other insulating material
that may be available on scene.
-
Cover
the patient’s head. It is estimated that between 40
and 60% of heat loss occurs in and around the head.
Heat loss can be minimized relatively easily by placing
a cap or hat on the subject.
-
If you
need to transport a subject, use layers—such as a sheet,
then blankets—wrapped around
patients who might become chilled easily. Blankets over
a patient are good; blankets wrapped around the patient
are better. Remember that heat loss can occur underneath
a person; if a situation requires extended contact with
the ground, take time to insulate them from the ground.
-
Prevent
wind exposure. Wind carries off body heat even on relatively
mild days. Think about it: if normal body temp is 98.6
degrees, a 55 degree breeze is more than 40 degrees
cooler.
-
Prevent
or minimize exposure to rain or snow. If the patient
gets wet on the way to the ambulance, remove wet coverings
and replace with dry.
-
Talk
to your subject. Ensure comfort and confirm heat loss
is minimized.
Of all subjects,
the elderly are at the highest risk for becoming cold. They
must be carefully monitored. They tend to have less lean
muscle mass or the metabolism to generate body heat through
use of the muscles they do have. They also tend to have
weak circulatory systems, as a general rule, and they may
not sense the cold well, either.
|
