Hypothermia

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

  • Breaking down of food during digestion (Metabolism)

  • Muscular energy (75% converted to heat)

  • Shivering

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