Important information about
Hypothermia, Frostbite, Frostnip, or Chilblains & how to prevent it.
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Hypothermia:
Being cold for too long can cause many cold-related illnesses
that are all grouped under the name (hy-po-ther-mee-uh)
In cold weather, your body may lose heat
faster than you can produce it. The result is hypothermia, or
abnormally low body temperature. Hypothermia is the opposite of
hyperthermia. Because the words sound alike, they are easily
confused. Hypothermia is a condition in which an organism's
temperature drops below that required for normal metabolism and
bodily function. In warm-blooded animals, core body temperature is
maintained near a constant level through biologic homeostasis. But
when the body is exposed to cold its internal mechanisms may be
unable to replenish the heat that is being lost to the organism's
surroundings. Anyone who spends much time outdoors in cold weather
can get hypothermia. You can also get it from being cold and wet, or
under cold water for too long. It can make you sleepy, confused and
clumsy. Because it happens gradually and affects your thinking, you
may not realize you need help. That makes it especially dangerous. A
body temperature below 95° F is a medical emergency and can lead to
death if not treated promptly.
Hypothermia
-
Occurs when the body’s core temperature
falls below 35°C
-
Air temperature of no great severity
can produce it
-
It’s onset can be so gradual that no
one, including the victim, may notice it until too late
-
Can occur at room temperature if an
individual is wet, inadequately clothed, drunk, chronically ill
or very old.
-
May affect the heart, lungs and other
major abdominal organs as well as the skin and soft tissues.
(see chilblains or frostbite)
People Susceptible to Hypothermia:
-
Elderly people are especially at risk.
-
Babies can get it from sleeping in a cold room.
-
Anyone exposed to extreme cold
-
People diagnosed with a Hypothalamic
disorder affecting thermoregulation
-
Anyone with a cardiovascular, neurological
or endocrine disease.
-
People who are suffering from Mental
illness, drug abuse, alcoholism and malnutrition
-
People with the following diseases:
Quadriplegia, severe Parkinson's, adrenal insufficiency,
hypothyroidism, & multiple sclerosis
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Cold-related Illnesses:
Frostbite
- frozen body tissue, most often the face, ears,
fingers or toes
Frostnip
- an early warning sign of frostbite that leaves
affected areas white and numb
Chilblains
- red, swollen skin caused by inflamed small blood
vessels
Thermoregulation:
Heat is produced by
Heat loss occurs by
-
Direct contact with a colder object
(Conduction)
-
Movement of air or water near to the skin
(Convection)
-
Infrared energy emissions (Radiation) which
cause approx. 65% of normal heat loss largely from the head and
neck area
-
Evaporation of sweat
-
Breathing
FACTORS WHICH INCREASE INJURY DUE TO THE COLD
-
Inadequate clothing and insulating from
the cold, particularly if wet
-
High wind chill factor
-
Immersion in cold water (21°C or less)
for longer than 15 – 20 minuets
-
Leanness (the only advantage of
obesity)
-
Fatigue – being tired or exhausted
-
Smoking
-
Poor nutrition
-
Age (very young or old)
-
Poor circulation (arterial disease,
tight clothing or shoes)
PREVENTION OF HYPOTHERMIA
-
Remove cold, wet clothing
-
Protect from wind and rain with suitable clothing (this will
often include a hat and gloves)
-
Rewarm (a) using blankets, sleeping
bags, body contact
-
(b) slowly using a
bath (40° – 42°C for the body trunk) but excluding arms and legs
-
Handle gently (vigorous activity may
cause cardiac arrest in extreme cases
-
Replace fluid loss – warm, sweet
fluids (e.g. 2 ½ % glucose solution)
-
provide
warm humidified air
-
Continue CPR when needed until warming
has occurred
PERFORMANCE
ENHANCEMENT
-
Physical performance decreases if the body
core temperature drops as little as 1°C, and shivering, may
occur.
-
Shivering interferes with coordination and
performance of fine movements and also depletes muscle stores of
glycogen (a storage form of energy) leading to early
fatigue and hypoglycemia (low blood sugar)
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Prevention
Prevention of hypothermia involves dressing warmly in cold
weather, avoiding adverse weather, maintaining adequate nutrition,
maintaining adequate indoor temperatures and regular checks on
elderly patients in cold weather. Patients with quadriplegia, who
cannot conserve heat by vasoconstriction or increase heat production
by shivering, are especially at risk of hypothermia if exposed to
cold environmental temperatures. In air, most heat is lost through the head; hypothermia can
thus be most effectively prevented by covering the head. Having
appropriate clothing for the environment is another important
prevention. Fluid-retaining materials like cotton can be a
hypothermia risk; if the wearer gets sweaty on a cold day, then
cools down, they will have sweat-soaked clothing in the cold air.
For outdoor exercise on a cold day, it is advisable to wear fabrics
which can "wick" away sweat moisture. These include wool or
synthetic fabrics designed specifically for rapid drying.
Heat is lost much faster in water. Children can
die of hypothermia in as little as two hours in water as warm as
16°C (61°F, 289K), typical of sea surface temperatures in temperate
countries such as Great Britain in early summer. Many seaside safety
information sources fail to quote survival times in water, and the
consequent importance of diving suits. This is possibly because the
original research into hypothermia mortality in water was carried
out in wartime Germany on unwilling subjects. There
is ongoing debate as to the ethical basis of using the data thus
acquired.
There is considerable evidence, however, that
children who suffer near-drowning accidents in water near 0°C (32°F,
273 K) can be revived up to two hours after losing consciousness.
The cold water considerably lowers metabolism, allowing the brain to
withstand a much longer period of hypoxia.
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Paradoxical undressing
20% to 50% of hypothermal deaths are associated with, or even
caused by, a phenomenon known as paradoxical undressing. When this
occurs, the hypothermic victim becomes seriously confused and starts
discarding clothing they have been wearing, a counter-productive
action which increases the rate of temperature loss. There have been
several published case studies of victims throwing off their clothes
before help reached them.
Rescuers who are trained in mountain survival
techniques have been taught to expect this effect. However, the
phenomenon still regularly leads police to incorrectly assume that
urban victims of hypothermia have been subjected to a sexual
assault.
One explanation for the effect is a
cold-inducted malfunction of the hypothalamus, the part of the brain
that regulates body temperature. Another explanation is that the
muscles contracting peripheral blood vessels become exhausted and
relax, leading to a sudden surge of blood (and heat) to the
extremities, fooling the victim into feeling warm.
Recognizing Hypothermia
Normal body temperature in humans is 37°C (98.6°F). Hypothermia
can be divided in three stages of severity. (See Table 1)
In stage 1, body temperature drops by 1-2°C
below normal temperature (1.8-3.6°F). Mild to strong shivering
occurs. The victim is unable to perform complex tasks with the
hands; the hands become numb. Blood vessels in the outer extremities
contract; lessening heat loss to the outside air. Breathing becomes
quick and shallow. Goose bumps form, raising body hair on end in an
attempt to create an insulating layer of air around the body
(limited use in humans due to lack of sufficient hair, but useful in
other species). Often, a person will experience a warm sensation, as
if they have recovered, but they are in fact heading into Stage 2.
Another test to see if the person is entering stage 2 is if they are
unable to touch their thumb with their little finger; this is the
first stage of muscles not working.
In stage 2, body temperature drops by 2-4°C
(3.6-7.2°F). Shivering becomes more violent. Muscle mis-coordination
becomes apparent. Movements are slow and labored, accompanied by a
stumbling pace and mild confusion, although the victim may appear
alert. Surface blood vessels contract further as the body focuses
its remaining resources on keeping the vital organs warm. The victim
becomes pale. Lips, ears, fingers and toes may become blue.
In stage 3, body temperature drops below
approximately 32°C (90°F). Shivering usually stops. Difficulty
speaking, sluggish thinking, and amnesia start to appear; inability
to use hands and stumbling are also usually present. Cellular
metabolic processes shut down. Below 30°C (86°F) the exposed skin
becomes blue and puffy, muscle coordination very poor, walking
nearly impossible, and the victim exhibits incoherent/irrational
behavior including terminal burrowing or even a stupor. Pulse and
respiration rates decrease significantly but fast heart rates
(ventricular tachycardia, atrial fibrillation) can occur. Major
organs fail. Clinical death occurs. Because of decreased cellular
activity in stage 3 hypothermia, the body will actually take longer
to undergo brain death.
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First AID
-
If any symptoms of hypothermia are present,
especially confusion or changes in mental status, the local
emergency service should be immediately contacted.
-
If the person is unconscious, check their
airway, breathing, and circulation. Pulse check should take at
least 45 seconds, as the heart rate may be extremely slow. If
necessary, begin rescue breathing or CPR. If the victim is
breathing less than 6 breaths per minute, begin rescue
breathing.
-
Take the person inside to room temperature
and cover him or her with warm blankets. If going indoors is not
possible, get the person out of the wind and use a blanket to
provide insulation from the cold ground. Cover the person's head
and neck to help retain body heat.
-
Once inside, remove any wet or constricting
clothes and replace them with dry clothing.
-
Warm the person. Apply warm compresses or
packs to the neck, chest wall, armpits and groin. If the person
is alert and can easily swallow, give warm, sweetened,
non-alcoholic fluids to aid the warming.
-
Stay with the person until medical help
arrives.
-
Assume that you should obtain a doctor if
the victim has been exposed for 24 hours or more.
-
Do not use direct heat (such as hot water,
a heating pad, or a heat lamp) to warm the person.
-
Do not give the person alcohol.
-
Do not rub the person's limbs because this
may cause further tissue damage.
-
Handle with extreme care and gently. Any
rough handling of an extremely hypothermic person could cause
their heart to stop.
-
It is also important not to give up
prematurely in resuscitative efforts. There are no reliable outcome
scores or predictors.
Rewarming
Techniques
Rewarming should be done expectantly, watching
for serious cardiac arrhythmias and afterdrop (a drop in core body
temperature associated with conduction of heat away from the core
during the rewarming surrounding cold tissues and vasodilatation),
and hypotension.
Simple rewarming techniques should begin in the
field. These include removing wet, cold clothing, covering with
warm, dry blankets, administering warmed intravenous fluids.
Active internal rewarming using IV fluids and
warmed medical air (core rewarming) should be used only when the
temperature is <32°C. The latter should be increased to 40-42°C to
prevent afterdrop. It is safest to perform vigorous rewarming in an
ICU setting however, because of cardiovascular
instability/complications. Other methods of increasing core
temperature more rapidly include use of cardiopulmonary bypass,
continuous arteriovenous rewarming or irrigation of the
gastrointestinal tract or body cavities.13 Monitoring core
temperature with an esophageal temperature probe or pulmonary artery
catheter should be considered for more accurate measurement of
'core' temperature. Cardiovascular support in the ICU is required.
In frail, elderly individuals the rewarming
should he done gradually to avoid cardiovascular collapse; a rate of
no more than 0.5°C/hour has been recommended.
Treatment of the underlying cause should be in
concert with rewarming. The administration of thiamine, antibiotics
or drug antagonists need not wait for correction of temperature.
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Hospital treatment
In a hospital, warming is accomplished by external techniques
(blankets, warming devices) for mild hypothermia and by more
invasive techniques such as warm fluids injected in the veins or
even lavage (washing) of the bladder, stomach, chest and abdominal
cavities with warmed fluids for severely hypothermic patients. These
patients are at high risk for arrhythmias (irregular heartbeats),
and care must be taken to minimize jostling and other disturbances
until they have been sufficiently warmed, as these arrhythmias are
very difficult to treat while the victim is still cold. An important
tenet of treatment is that a person is not dead until they are warm
and dead. Remarkable accounts of recovery after prolonged cardiac
arrest have been reported in patients with hypothermia. This is
presumably because the low temperature prevents some of the cellular
damage that occurs when blood flow and oxygen are lost for an
extended period of time.
Pathophysiology
Hypothermia is due to a disturbance in the net regulation of
heat production and heat loss weighted towards the latter. This can
result from defective homeostatic regulation, reduced metabolism
(including diminished cellular metabolism and shivering), or
increased loss from exposure to extreme cold or impaired
cardiovascular response, especially loss of vasomotor tone.
Acute hypothermia is usually the result of
submersion in cold water, sub acute hypothermia often results from
cold air while chronic hypothermia relates to underlying disease
with disordered or insufficient auto regulation.
Metabolic processes slow and cerebral blood
flow diminishes about 6% for each 10°C decrease in body temperature.
At 28°C the metabolic rate falls to half normal. At less than 25°C
the patient looks dead and has asystole.
With severe hypothermia of 25°C there is loss
of cerebrovascular autoregulation. Cerebral blood flow declines in
a pressure passive manner along with systemic blood pressure fall.
EEG synaptic activity fails.
Both intrinsic and extrinsic coagulation
systems are affected in hypothermia. Platelet function becomes
ineffective because thromboxane B2 is inhibited Fibrinolytic
activity is increased. A heparin-like substance is released. Reduced
enzyme activities necessary to initiate and maintain platelet-fibrin
clots results in net increase in bleeding tendency. These features
produce a disseminated intravascular coagulation-like syndrome but
with a marked hemorrhagic tendency. This can be aggravated in the
hypothermic trauma patient who may require massive transfusions for
blood loss.
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Clinical Features
Clinical features of mild hypothermia include shivering,
tachycardia, tachypnea, diuresis, peripheral cyanosis. It is
important to feel the temperature of the trunk. In hypothermia the
trunk and normally warm regions such as the axillae, groins are
cold. A low-reading thermometer should he used to take a rectal
temperature. The patient with chronic hypothermia may resemble one
with hypothyroidism with puffy facies, slow hoarse speech and mental
changes. The skin has a doughy consistency. Neurological features
include dysarthria, ataxia and amnesia.
With worsening, the pulse gets weaker and
slower, shivering ceases, respirations are slow and shallow and the
patient becomes very pale. Deep tendon reflexes are increased above
32°C; hyporeflexia occurs between 26-32°C and areflexia is present
below 26°C. Confusion worsens sometimes to delirium and muscular
rigidity develops. Further deterioration leads to stupor or coma.
Coma does not usually occur above 28°C; other causes for coma should
be sought if the patient is comatose with a core T of >28°C. The
pupils may become fixed to light; the heart may develop ventricular
fibrillation without palpable pulse or audible heart beat.
The clinical context of the hypothermia is
often the best clue to the underlying cause. Environmental exposure
to cold or a history or findings or a high cervical cord lesion,
polyneuropathy, hypothyroidism are usually obvious. The patient who
presents with hypothermia in the summer usually has a serious
illness, e.g., Wernicke's encephalopathy (even if ocular movement
abnormalities are not present), sepsis, drug overdose (e.g.,
neuroleptics, high dose barbiturates) or, sometimes combinations of
causes.4
Laboratory Features
The EEG develops evolutionary changes with generalized slowing
beginning at 30°C, then changes to a burst-suppression pattern by
20-22°C and becomes flat at 18°C. Evoked responses are less
affected. At 29°C, wave forms are delayed by 33% but are still
identifiable. Latencies become lengthened progressively to
unrecordable levels as 19°C is approached and waveforms may
disappear altogether.6 7 Barbiturates and hypoxia modify the evoked
responses to hypothermia.8 Transcranial motor evoked responses
increase in amplitude and latency to reach a maximum at 28°C.9 This
effect is modified by anesthesia and carbon dioxide concentration.
A series of cardiac abnormalities occurs with
progressive hypothermia: obscured P waves, prolonged PR, QRS and QT
intervals, atrial fibrillation and ventricular dysrhythmias.
Ventricular fibrillation may develop at or < 28°C.
Serum potassium should be checked, as
hyperkalemia is a common accompaniment.10 A coagulation screen
should probably be performed. Tests to confirm or exclude diagnostic
impressions for the underlying cause are usually necessary, but are
context-dependent (see above).
As a general policy, patients found in an
acute hypothermic situation should not be pronounced dead until they
are assessed after rewarming to at least 33°C core temperature.
Outcome / Prognosis
An overall mortality associated with
hypothermia is about 17%. This involves all ages, etiologies and
classifications of hypothermia Those with extreme hyperkalernia
(mean serum potassium of 14.5 mmol/L) are always in cardiopulmonary
arrest and have a poor prognosis for successful resuscitation
(Schaller et al.1990). Markedly elevated serum ammonia is also a
marker of cell lysis.
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Hypothermia can be divided into accidental,
primary and secondary (Table 1).
Table 1. Classification of Hypothermia
Type |
Cause |
Examples |
Accidental
|
Exposure to extreme cold
|
Outdoor activities; falls with immobilization in
cold indoors |
Primary
|
Hypothalamic disorder affecting thermoregulation
|
Hypothalarnic lesion,Wernicke's encephalopathy,
Spontaneous cyclic hypothermia, congenital CNS
abnormalities |
Secondary
|
Underlying cardiovascular, neurological or
endocrine disease. Mentall illness, drug abuse,
alcoholism and malnutrition may contribute. |
Quadriplegia, severe Parkinsonism, autonomic
neuropathy (affecting efferent flow), adrenal
insufficiency, hypothyroidism, Wernicke's
encephalopathy, advanced sepsis, alcohol or
drugs, multiple sclerosis (hypothalamic
involvement |
Table 2: Severity Classification of Hypothermia
Level of Hypothermia |
Temeperature
Range |
Physiological
Effect |
Mild |
36.5-32°C |
Catecholamine
release - Peripheral vasoconstriction - Increased
ventiIatory rate - Cold induced diuresis Confusion, Faulty
judgment Shivering, hyppfcnexia |
Moderate |
32-28°C |
Decreased metabolic
rate. Decreased oxygen consumption, enzyme suppression,
sympathetic nervous reduction, hyporeflexia, coagulopathies,
decreased ventilation rate, stupor |
Severe |
28-20°C |
Metabolic acidosis,
increased cardiac irritability, ventricular fibrillation,
severe hypotension, decreased or absent ventilation,
hyperkalemia, coma |
Profound |
<20°C
|
asystole, mimic
brain death, flat EEG |
DISCLAIMER
The information in this website is of a general nature.
Individual circumstances may require modification of general advice
from an appropriate health professional eg Doctor.
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This website was last updated on:07/22/2011