Skip to main content
Select Source:

Hypothermia

Hypothermia

Definition

Hypothermia, a potentially fatal condition, occurs when body temperature falls below 95°F (35°C).

Description

Although hypothermia is an obvious danger for people living in cold climates, many cases have occurred when the air temperature is well above the freezing mark. Elderly people, for instance, have succumbed to hypothermia after prolonged exposure to indoor air temperatures of 50-65°F (10-18.3°C). In the United States, hypothermia is primarily an urban phenomenon associated with alcoholism, drug addiction, mental illness, and coldwater immersion accidents. The victims are often homeless male alcoholics. Officially, 11,817 deaths were attributed to hypothermia in the United States from 1979 to 1994, but experts suspect that many fatal cases go unrecognized. Nearly half the victims were 65 or older, with males dominating every age group. Nonwhites were also overrepresented in the statistics. Among males 65 and older, nonwhites outnumbered whites by more than four to one.

Causes and symptoms

Measured orally, a healthy person's body temperature can fluctuate between 97°F (36.1°C) and 100°F (37.8°C). Survival depends on maintaining temperature stability within this range by balancing the heat produced by metabolism with the heat lost to the environment through (for the most part) the skin and lungs. When environmental or other changes cause heat loss to outpace heat production, the brain triggers physiological and behavioral responses to restore the balance. The involuntary muscular activity of shivering, for example, aids heat production by accelerating metabolism. But if the cold stress is too great and the body's defenses are overwhelmed, body temperature begins to fall. Hypothermia is considered to begin once body temperature reaches 95°F (35°C), though even smaller drops in temperature can have an adverse effect.

Hypothermia is divided into two types: primary and secondary. Primary hypothermia occurs when the body's heat-balancing mechanisms are working properly but are subjected to extreme cold, whereas secondary hypothermia affects people whose heat-balancing mechanisms are impaired in some way and cannot respond adequately to moderate or perhaps even mild cold. Primary hypothermia typically involves exposure to cold air or immersion in cold water. The cold air variety usually takes at least several hours to develop, but immersion hypothermia will occur within about an hour of entering the water, since water draws heat away from the body much faster than air does. In secondary hypothermia, the body's heat-balancing mechanisms can fail for any number of reasons, including strokes, diabetes, malnutrition, bacterial infection, thyroid disease, spinal cord injuries (which prevent the brain from receiving crucial temperature-related information from other parts of the body), and the use of medications and other substances that affect the brain or spinal cord. Alcohol is one such substance. In smaller amounts it can put people at risk by interfering with their ability to recognize and avoid cold-weather dangers. In larger amounts it shuts down the body's heat-balancing mechanisms.

Secondary hypothermia is often a threat to the elderly, who may be on medications or suffering from illnesses that affect their ability to conserve heat. Malnutrition and immobility can also put the elderly at risk. Some medical research suggests as well that shivering and blood vessel narrowingtwo of the body's defenses against coldmay not be triggered as quickly in older people. For these and other reasons, the elderly can, over a period of days or even weeks, fall victim to hypothermia in poorly insulated homes or other surroundings that family, friends, and caregivers may not recognize as life threatening. Another risk for the elderly is the fact that hypothermia can easily be misdiagnosed as a stroke or some other common illness of old age.

The signs and symptoms of hypothermia follow a typical course, though the body temperatures at which they occur vary from person to person depending on age, health, and other factors. The impact of hypothermia on the nervous system often becomes apparent quite early. Coordination, for instance, may begin to suffer as soon as body temperature reaches 95°F (35°C). The early signs of hypothermia also include cold and pale skin and intense shivering; the latter stops between 90°F (32.2°C) and 86°F (30°C). As body temperature continues to fall, speech becomes slurred, the muscles go rigid, and the victim becomes disoriented and experiences eyesight problems. Other harmful consequences include dehydration as well as liver and kidney failure. Heart rate, respiratory rate, and blood pressure rise during the first stages of hypothermia, but fall once the 90°F (32.2°C) mark is passed. Below 86°F (30°C) most victims are comatose, and below 82°F (27.8°C) the heart's rhythm becomes dangerously disordered. Yet even at very low body temperatures, people can survive for several hours and be successfully revived, though they may appear to be dead.

Diagnosis

Information on the patient's prior health and activities often helps doctors establish a correct diagnosis and treatment plan. Pulse, blood pressure, temperature, and respiration require immediate monitoring. Because the temperature of the mouth is not an accurate guide to the body's core temperature, readings are taken at one or two other sites, usually the ear, rectum, or esophagus. Other diagnostic tools include electrocardiography, which is used to evaluate heart rhythm, and blood and urine tests, which provide several kinds of key information; a chest x ray is also required. A computed tomography scan (CT scan) or magnetic resonance imaging (MRI) may be needed to check for head and other injuries.

Treatment

Emergency medical help should be summoned whenever a person appears hypothermic. The danger signs include intense shivering; stiffness and numbness in the arms and legs; stumbling and clumsiness; sleepiness, confusion, disorientation, amnesia, and irrational behavior; and difficulty speaking. Until emergency help arrives, a victim of outdoor hypothermia should be brought to shelter and warmed by removing wet clothing and footwear, drying the skin, and wrapping him or her in warm blankets or a sleeping bag. Gentle handling is necessary when moving the victim to avoid disturbing the heart. Rubbing the skin or giving the victim alcohol can be harmful, though warm drinks such as clear soup and tea are recommended for those who can swallow. Anyone who aids a victim of hypothermia should also look for signs of frostbite and be aware that attempting to rewarm a frostbitten area of the body before emergency help arrives can be extremely dangerous. For this reason, frostbitten areas must be kept away from heat sources such as campfires and car heaters.

Rewarming is the essence of hospital treatment for hypothermia. How rewarming proceeds depends on the body temperature. Different approaches are used for patients who are mildly hypothermic (the patient's body temperature is 90-95 °F [32.2-35 °C]), moderately hypothermic (86-90 °F [30-32.2 °C]), or severely hypothermic (less than 86 °F [30 °C]). Other considerations, such as the patient's age or the condition of the heart, can also influence treatment choices.

Mild hypothermia is reversed with passive rewarming. This technique relies on the patient's own metabolism to rewarm the body. Once wet clothing is removed and the skin is dried, the patient is covered with blankets and placed in a warm room. The goal is to raise the patient's temperature by 0.5-2 °C an hour.

Moderate hypothermia is often treated first with active external rewarming and then with passive rewarming. Active external rewarming involves applying heat to the skin, for instance by placing the patient in a warm bath or wrapping the patient in electric heating blankets.

Severe hypothermia requires active internal rewarming, which is recommended for some cases of moderate hypothermia as well. There are several types of active internal rewarming. Cardiopulmonary bypass, in which the patient's blood is circulated through a rewarming device and then returned to the body, is considered the best, and can raise body temperature by 1-2 °C every 3-5 minutes. However, many hospitals are not equipped to offer this treatment. The alternative is to introduce warm oxygen or fluids into the body.

Hypothermia treatment can also include, among other things, insulin, antibiotics, and fluid replacement therapy. When the heart has stopped, both cardiopulmonary resuscitation (CPR) and rewarming are necessary. Once a patient's condition has stabilized, he or she may need treatment for an underlying problem such as alcoholism or thyroid disease.

Prognosis

Victims of mild or moderate hypothermia usually enjoy a complete recovery. In regard to severely hypothermic patients, the prognosis for survival varies due to differences in people's physiological responses to cold.

KEY TERMS

Antibiotics Substances used against microorganisms that cause infection.

Computed tomography A process that uses x rays to create three-dimensional images of structures inside the body.

Esophagus A muscular tube through which food and liquids pass on their way to the stomach.

Insulin A substance that regulates blood glucose levels. Glucose is a sugar.

Magnetic resonance imaging The use of electromagnetic energy to create images of structures inside the body.

Metabolism The chemical changes by which the body breaks down food and other substances and builds new substances necessary for life.

Nervous system The system that transmits information, in the form of electrochemical impulses, throughout the body. It comprises the brain, spinal cord, and nerves.

Rectum The lower section of the large intestine. The intestines are part of the digestive system.

Stroke A condition involving loss of blood flow to the brain.

Thyroid A gland (fluid-secreting structure) in the neck. It plays an important role in metabolism.

Prevention

People who spend time outdoors in cold weather can reduce heat loss by wearing their clothing loosely and in layers and by keeping their hands, feet, and head well covered (30-50% of body heat is lost through the head). Because water draws heat away from the body so easily, staying dry is important, and wet clothing and footwear should be replaced as quickly as possible. Wind- and water-resistant outer garments are also crucial. Alcohol should be avoided because it promotes heat loss by expanding the blood vessels that carry body heat to the skin.

Preventing hypothermia among the elderly requires vigilance on the part of family, friends, and caregivers. An elderly person's home should be properly insulated and heated, with living areas kept at a temperature of 70 °F (21.1 °C). Warm clothing and bedding are essential, as are adequate food, rest, and exercise; warming the bed and bedroom before going to sleep is also recommended. Older people who live alone should be visited regularlyat least once a day during very cold weatherto ensure that their health remains sound and that they are taking good care of themselves. For help and advice, family members and others can turn to government and social service agencies. Meals on wheels and visiting nurse programs, for instance, may be available, and it may be possible to obtain financial aid for winterizing and heating homes.

Resources

BOOKS

Petty, Kevin J. "Hypothermia." In Harrison's Principles of Internal Medicine, edited by Anthony S. Fauci, et al. New York: McGraw-Hill, 1997.

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"Hypothermia." Gale Encyclopedia of Medicine, 3rd ed.. . Encyclopedia.com. 14 Nov. 2018 <https://www.encyclopedia.com>.

"Hypothermia." Gale Encyclopedia of Medicine, 3rd ed.. . Encyclopedia.com. (November 14, 2018). https://www.encyclopedia.com/medicine/encyclopedias-almanacs-transcripts-and-maps/hypothermia

"Hypothermia." Gale Encyclopedia of Medicine, 3rd ed.. . Retrieved November 14, 2018 from Encyclopedia.com: https://www.encyclopedia.com/medicine/encyclopedias-almanacs-transcripts-and-maps/hypothermia

Learn more about citation styles

Citation styles

Encyclopedia.com gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).

Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

http://www.mla.org/style

The Chicago Manual of Style

http://www.chicagomanualofstyle.org/tools_citationguide.html

American Psychological Association

http://apastyle.apa.org/

Notes:
  • Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most Encyclopedia.com content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
  • In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.

hypothermia

hypothermia has been reported during marathons, on the mountains, in caving and canoeing, at work on land and at sea, and in and under water. It may occur, even during the summer, among the elderly and the very young, in the operating theatre, and in association with some medical disorders. Geographically hypothermia has in fact been recorded from most parts of the world even at low altitudes in the Sahara and from tropical Kampala.

Thermally the body can be divided into zones. The temperature of the ‘core’, including the vital organs, heart, and brain, is kept stable over a surprising range of environmental conditions. The ‘shell’ is superficial, and its size and temperature varies considerably. Hypothermia is defined as a core temperature below 35°C. However, hypothermia is not a diagnosis, but a sign that changes must have occurred in the body, which vary with the circumstances which have led to cooling. During cold exposure the body ‘burns’ carbohydrate to generate heat and the amount of fuel left depends on the rate of cooling. Also fluid is lost through increased urine output, and there are complex movements of fluids in the body, related in magnitude to the duration of exposure to cold, which reverse during rewarming. There are therefore different types of hypothermia.(i) In ‘immersion’ hypothermia the cold stress is so great that the body's heat-generating capacity is overwhelmed and the core temperature is forced down. Because energy reserves are available, the person will have very little difficulty in rewarming once removed from the severe environment. Falling into cold water is the commonest accidental cause, and hypothermia deliberately induced for medical reasons is of this type.(ii) In ‘exhaustion’ hypothermia the body maintains the temperature until energy sources are exhausted. Then, since the heat-generating ability is reduced, even relatively mild cold exposure may cause continued cooling. Thermal protection must therefore take account of every avenue of heat loss, because even small variations of available heat may make the difference between life and death. This is the type most commonly found in mountaineers or hill walkers.(iii) With ‘urban’ hypothermia, the cold has been mild but prolonged. The core temperature remains normal (35°C or above) possibly for days or weeks, with massive fluid shifts. The temperature eventually drifts down, or faster cooling is precipitated by some other factor such as a fall. This is the most usual type found in the elderly or in association with malnutrition.(iv) ‘Submersion’ hypothermia occurs in people who have been totally submerged in very cold water. Recovery has been known even after 15–60 min (typical submersion survival is about 3 min). Survival, more likely in children, depends on resuscitation being started immediately on rescue.

The case history distinguishes the different types, though they may overlap. A climber in a snowstorm disabled by a broken leg will cool as rapidly as if immersed, because the shock of the injury increases the rate of heat loss, and the fracture prevents heat generation from voluntary activity or shivering. A deep diver may suffer ‘immersion’ hypothermia, even in a dry pressure chamber, because of the tremendous heat transfer capacity of the compressed oxyhelium gas mixture which he is breathing. A swimmer lost overboard in relatively warm water is a candidate for ‘exhaustion’ hypothermia. A middle-aged man or a child with severe malnutrition is likely to develop ‘urban’ hypothermia, whereas a fit 70-year-old out walking in the hills would be liable to ‘exhaustion’ hypothermia.

When a person is in a situation where hypothermia is imminent there is a great temptation to continue to move in order both to keep generating heat from the activity and to escape the situation. This may not be the best option for survival, since the activity increases the rate of heat loss and aggravates exhaustion. The best prospect of survival at sea is not to try to swim but to stay with a capsized boat. Similarly in the hills in bad weather the macho response of trying to battle a way out has resulted in many deaths, whereas those who ‘go to ground’ — taking shelter until the weather improves — usually survive.

A variety of signs and symptoms of hypothermia have been described (see table). However there is great individual variation. For example, loss of consciousness may occur at a core temperature as high as 33°C, but in one case consciousness was still present at a rectal temperature of 24.3°C, and other causes of unconsciousness may confuse the issue. Shivering is considered to cease usually at 30°C — but shivering has been recorded at a core temperature of 24°C. At the other extreme some experimental subjects can cool without shivering and many mountain rescue cases never shiver.

Signs and symptoms in hypothermia

Core temperature °C

37.6

‘Normal’ rectal temperature.

37

‘Normal’ oral temperature.

36

Increased metabolic rate to balance heat loss. Breathing and pulse faster.

35

Shivering at a maximum.

Reflexes exaggerated; speech disordered; thinking slowed.

34

Usually responsive; normal blood pressure.

Lower limit compatible with continued exercise.

33–31

Retrograde amnesia; consciousness clouded; blood pressure low; pupils dilated;

shivering usually ceased.

30–28

Progressive loss of consciousness; increased muscular rigidity;

slow pulse and respiration; irregular heart beat.

Susceptible to ventricular fibrillation if heart mechanically irritated.

27

Voluntary movement lost.

26

Pupillary light reflex and deep tendon and skin reflexes lost.

Victims seldom conscious.

24–21

100% mortality in shipwreck victims in World War II

20

Heart standstill.

17

No electrical activity in brain.

14.4

Lowest known accidental hypothermic patient with recovery.

9

Lowest artificially cooled hypothermic patient with recovery.

4

Monkeys revived successfully.

1–7

Rats and hamsters revived successfully.



Diagnosis requires measurement of core temperature, usually rectal, but since this route may not be practical in the field, the person should be treated as a ‘cold casualty’ if the armpit feels ‘as cold as marble’ to the rescuer's hand. In hypothermia the diagnosis of other accompanying conditions is difficult. Slurred speech, staggering, incoordination or a change in personality may be due to hypothermia and not necessarily brain damage. In hypothermia the reflexes are affected and there is stiffness of the muscles; there are changes in the electrical and mechanical functions of the heart; and the lungs may show clinical and X-ray features similar to pneumonia, though these clear on rewarming. It is therefore important that the patient should be restored to normal body temperature before any diagnosis is made or any irrevocable treatment started.

If the heart stops, the lack of circulation, and therefore of oxygen supply to the brain would ordinarily cause permanent brain damage in about three minutes. Although hypothermia can give some protection for the brain by prolonging the time before oxygen lack causes permanent damage, it is cardiac function that is most important for survival. As the heart cools it becomes more susceptible to ventricular fibrillation (VF) (an uncoordinated electrical activity of the heart which produces no actual pumping of blood). This may be triggered by mechanical irritation (which may be as mild as rolling a patient for bedmaking), by hypoxia of the heart muscle, or by rapid changes in pH or electrolytes in the blood, or in temperature gradients within the heart muscle. Inappropriate rewarming techniques add to the hazard.

Rescue and care

Profound accidental hypothermia can be very difficult to distinguish from death. The only certain diagnosis of death in hypothermia is failure to recover on rewarming. However hypothermia is seldom present in isolation. Victims may also be injured or have some illness, possibly cold-related. In water, drowning may precede or follow cooling. If neither heart nor breathing activity can be detected and there is evidence that the person was alive within the previous two hours, the rescuers should start resuscitation, though only if this can be continued until the casualty has been rewarmed or has reached hospital: otherwise members of the rescue team will become exhausted and may then become hypothermic casualties themselves. Also, the heart may occasionally still be beating and providing some circulation, even when this cannot be detected; the mechanical effects of active resuscitation attempts may trigger ventricular fibrillation, and the patient would then be in a worse state and needing continuing resuscitation.

Evan L. Lloyd

Bibliography

Lloyd, E. L. (1986). Hypothermia and cold stress. Croom Helm, London.


See also cold exposure; near-drowning; survival at sea; temperature regulation.

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"hypothermia." The Oxford Companion to the Body. . Encyclopedia.com. 14 Nov. 2018 <https://www.encyclopedia.com>.

"hypothermia." The Oxford Companion to the Body. . Encyclopedia.com. (November 14, 2018). https://www.encyclopedia.com/medicine/encyclopedias-almanacs-transcripts-and-maps/hypothermia-0

"hypothermia." The Oxford Companion to the Body. . Retrieved November 14, 2018 from Encyclopedia.com: https://www.encyclopedia.com/medicine/encyclopedias-almanacs-transcripts-and-maps/hypothermia-0

Learn more about citation styles

Citation styles

Encyclopedia.com gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).

Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

http://www.mla.org/style

The Chicago Manual of Style

http://www.chicagomanualofstyle.org/tools_citationguide.html

American Psychological Association

http://apastyle.apa.org/

Notes:
  • Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most Encyclopedia.com content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
  • In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.

Hypothermia

Hypothermia

An important facet of a forensic investigation into a death is the determination of the cause of death . In cases where outward signs of physical trauma (i.e., gunshot or stab wounds) are absent, a forensic investigator may be presented with more subtle indicators of death.

One example is hypothermia; the intentional or accidental reduction of core body temperature to below 95°F (35°C) which, in severe instances, is fatal. Humans are endothermic (warm-blooded) creatures, whose core body temperature is physiologically regulated at approximately 98.6°F (37°C), even in fluctuating environmental temperatures. An abnormal rise in this core temperature can cause heat stroke, with an abnormal decrease representing hypothermia.

Intentional hypothermia is used in medicine in both regional and total-body cooling. The body's metabolic rate (the rate at which cells provide energy for the body's vital functioning) decreases 8% with each 1.8°F (1°C) reduction in core body temperature, thus requiring reduced amounts of oxygen. Total-body hypothermia lowers the body temperature and slows the metabolic rate, protecting organs from reduced oxygen supply during the interruption of blood flow necessary in certain surgical procedures. In some procedures, like heart repair and organ transplantation, individual organs are preserved by intentional hypothermia of the organ involved. In open-heart surgery, blood supply to the chilled heart can be totally interrupted while the surgeon repairs the damaged organ. Organ and tissue destruction using extreme hypothermia -212 to -374°F (-100 to -190°C) is utilized in retinal and glaucoma surgery and to destroy pre-cancerous cells in some body tissue. This is called cryosurgery.

In contrast to these beneficial uses of intentional hypothermia, accidental hypothermia (i.e., falling into icy water, or exposure to cold weather without appropriate protective clothing) is potentially fatal and is of forensic interest.

Hypothermia is classified into four states. In mild cases, 9589.6°F (3532°C), symptoms include feeling cold, shivering (which helps raise body temperature), increased heart rate, and a desire to urinate, and some loss of coordination. Moderate hypothermia, 87.878.8°F (3126°C) causes a decrease or inhibition of shivering, along with weakness, sleepiness, confusion, slurred speech, and lack of coordination. Deep hypothermia, 7768°F (2520°C) is extremely dangerous, as the body can no longer produce heat. Sufferers may behave irrationally, become comatose, lose the ability to see, and often cannot follow commands. In profound cases, 6657°F (1914°C), the sufferer will become rigid and may even appear dead, with dilated pupils, extremely low blood pressure, and barely perceptible heartbeat and breathing. This state usually requires complete, professional cardiopulmonary resuscitation for survival.

Normally, the body's core temperature represents a homeostatic balance between heat generation due to metabolic processes, and the loss of heat through conduction, convection, evaporation, and respiration, and radiation.

Conduction occurs when direct contact is made between the body and a cold object, and heat passes from the body to that object. Convection is when cold air or water makes contact with the body, becomes warm, and moves away to be replaced by another volume of cold air or water. The cooler the air or water, and the faster it moves, the faster the core body temperature drops.

Evaporation through perspiration and respiration provides almost 30% of the body's natural cooling mechanism. Because cold air contains little water and readily evaporates perspiration; and because physical exertion produces sweating, even in extreme cold, heat loss through evaporation takes place even at very low temperatures. When heat loss involves both evaporation and convection, for instance when someone is outdoors in wet clothes, body temperature can quickly plummet to dangerously low levels.

see also Death, cause of; Death, mechanism of.

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"Hypothermia." World of Forensic Science. . Encyclopedia.com. 14 Nov. 2018 <https://www.encyclopedia.com>.

"Hypothermia." World of Forensic Science. . Encyclopedia.com. (November 14, 2018). https://www.encyclopedia.com/science/encyclopedias-almanacs-transcripts-and-maps/hypothermia

"Hypothermia." World of Forensic Science. . Retrieved November 14, 2018 from Encyclopedia.com: https://www.encyclopedia.com/science/encyclopedias-almanacs-transcripts-and-maps/hypothermia

Learn more about citation styles

Citation styles

Encyclopedia.com gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).

Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

http://www.mla.org/style

The Chicago Manual of Style

http://www.chicagomanualofstyle.org/tools_citationguide.html

American Psychological Association

http://apastyle.apa.org/

Notes:
  • Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most Encyclopedia.com content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
  • In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.

Hypothermia

HYPOTHERMIA

DEFINITION


Hypothermia (pronounced hi-po-ther-mee-ah) occurs when the body temperature falls below 95°F (35°C). The condition is often fatal.

DESCRIPTION


People who live in cold climates are obviously at risk for hypothermia. They may be stranded out of doors overnight without protection from the cold. Their body temperatures may drop so low that they develop hypothermia. Eventually, they may freeze to death.

Hypothermia also occurs in more moderate climates during cold weather. The problem is more likely to occur among elderly and homeless people. Elderly people may not remember to keep their homes heated properly. Or they may be too poor to pay their heating bills. Their homes may remain at a constant temperature of 50° to 65°F (10° to 17°C). A continuous exposure to this temperature can cause hypothermia.

Homeless people may have to spend most of their lives out of doors. In cold weather, their body temperatures may drop to dangerously low levels. Official records indicate that nearly twelve thousand homeless people died of hypothermia between 1979 and 1994. However, these numbers are probably not accurate. Many deaths of homeless people from hypothermia probably go unreported.

Males, non-whites, and alcoholics are at high risk for hypothermia. These groups make up a large fraction of the homeless population.

Hypothermia: Words to Know

Electrocardiogram:
A test used to determine the electrical activity of the heart to see if it is functioning normally.
Frostbite:
A medical condition in which some part of the body has become frozen.
Malnutrition:
A condition in which a person is not eating enough of the right kinds of foods.
Stroke:
A serious medical condition caused by a loss of blood flow to the brain.
Thyroid:
An organ that controls a number of important bodily functions.

CAUSES


The human body functions normally over a very narrow range of temperatures. If body temperature goes higher than about 100°F (38°C) or lower than about 97°F (36°C), problems develop. The chemical changes that take place in cells begin to occur either too rapidly or too slowly. At low temperatures, those chemical changes may slow down so much that the body ceases to function entirely. That condition is known as hypothermia.

Hypothermia is divided into two types: primary and secondary. Primary hypothermia occurs when the body's heat-balancing mechanisms are working properly but the body is subjected to extremely cold conditions. For example, a person might fall into an icy lake. The conditions are so cold that hypothermia develops in spite of the otherwise healthy body.

In secondary hypothermia, the body's heat-balancing mechanisms are not working properly. Hypothermia may develop even if a person is exposed to even mildly cold conditions. Some conditions that can cause secondary hypothermia are stroke (see stroke entry), diabetes (see diabetes mellitus entry), malnutrition, bacterial infection, thyroid condition, spinal cord injury (see spinal cord injury entry), and the use of certain medications and other substances. Alcohol is one such substance. It can interfere with portions of the heat-balancing system. A person may not recognize when he or she is becoming dangerously cooled.

Secondary hypothermia is often a threat to the elderly. They are likely to be on medications or suffering from some medical condition that can cause secondary hypothermia. Elderly people sometimes keep their homes cool to save money on heating costs. They may develop hypothermia even if the temperature is no colder than 60°F (15.5°C).

SYMPTOMS


The signs and symptoms of hypothermia follow a typical course. Though the body temperature at which they occur vary from person to person depending on age, health, and other factors.

Some of the first signs of hypothermia may be lack of coordination, cold and pale skin, and intense shivering. As body temperature begins to fall, speech becomes slurred, muscles go rigid, vision problems develop, and the patient becomes disoriented.

At body temperatures below 90°F (32°C), heart rate, respiratory (breathing) rate, and blood pressure fall. Eventually the patient loses consciousness and may appear to be dead. At even very low temperatures, however, a person may survive for several hours. They can sometimes be successfully revived.

DIAGNOSIS


The situation in which a person is found is often an important clue to diagnosis. Someone pulled from a lake in the middle of winter, for example, is likely to be suffering from hypothermia. Pulse, blood pressure, temperature, and respiration should be checked immediately and monitored. Oral (mouth) temperatures are often not accurate at cold temperatures. Instead, the temperature is taken at some other part of the body, such as in the ear or rectum.

A doctor might use an electrocardiogram (ECG; pronounced ih-LEK-trocar-DEE-uh-gram; it measure electrical activity of the heart to make sure it is functioning normally) to get information on the functioning of the patient's heart. Blood and urine tests may also be ordered to see how well body functions are operating.

TREATMENT


A person with hypothermia requires immediate medical attention. First aid for such patients is not as obvious as it may seem, however. For example, rubbing the patient's skin or giving him or her a drink of alcohol can be dangerous. Also, the patient should be checked for signs of frostbite (see frostbite entry). Attempting to warm a frostbitten area can be very dangerous.

The first step is to move the patient to a warm, dry location. Gentle handling is necessary to void disturbing the heart. Giving the patient a warm drink can be helpful if he or she can swallow.

Once a patient has reached the hospital, the warming procedure depends on the seriousness of the patient's condition. The stage of hypothermia is defined by the patient's body temperature. The three stages of hypothermia and the temperatures at which they occur are as follows:

  • Mild hypothermia: 90° to 95°F (32° to 35°C)
  • Moderate hypothermia: 86° to 90°F (30° to 32°C)
  • Severe hypothermia: less than 86°F (30°C)

Mild hypothermia is treated with passive rewarming. That is, the patient's body is allowed to come back to its normal temperature on its own. Wet clothing is removed and the patient is covered with blankets and placed in a warm room.

Moderate hypothermia is first treated with active rewarming. That is, the patient is wrapped in an electric heating blanket or placed in a warm bath. As his or her temperature begins to rise, these aids are removed. The body is allowed to return to its normal temperature on its own.

Severe hypothermia usually requires internal rewarming. Some method is needed to start warming the patient's internal organs and tissues. For example, patients may be provided with warm oxygen to breathe. Or they may be given warm fluids to drink. In extreme cases, a procedure known as a cardiopulmonary bypass may be used. In this procedure, a tube is inserted into the patient's blood vessels. Blood is directed out of the body and through an external machine. The external machine warms up the blood. The blood is then returned to the body. This treatment is not available in all hospitals.

PROGNOSIS


People who experience mild or moderate hypothermia usually enjoy a complete recovery. The prognosis for people who experience severe hypothermia is less certain. Recovery depends on a number of factors, such as the person's own body chemistry and how soon treatment was provided.

PREVENTION


Hypothermia can be prevented by following some simple rules. First, people who have to spend time outdoors in cold weather should wear adequate clothing. Head covering is especially important since 30 to 50 percent of body heat is lost through the head. Clothing should also be kept as dry as possible. Water absorbs heat faster than air, so wet clothes cause body temperature to drop quickly. Alcoholic beverages should be avoided also. Alcohol causes blood vessels to expand, causing the body to lose heat faster.

For a number of reasons, hypothermia is a special problem among elderly people. They may be subject to a variety of medical problems that make them more sensitive to cold temperatures. The medications they take may also make them more subject to hypothermia. Elderly people sometimes forget to take necessary precautions against chills, such as keeping the house warm enough and getting adequate meals.

Friends and neighbors can play an important role in preventing the elderly from developing hypothermia. They can check up on older relatives and friends to make sure that they continue to take necessary precautions against hypothermia.

FOR MORE INFORMATION


Forgey, William W. The Basic Essentials of Hypothermia. Guilford, CT: Globe, Pequot Press, 1999.

Hall, Christine B. Cold Can Kill: Hypothermia. University of Alaska Sea Grant, 1994.

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"Hypothermia." UXL Complete Health Resource. . Encyclopedia.com. 14 Nov. 2018 <https://www.encyclopedia.com>.

"Hypothermia." UXL Complete Health Resource. . Encyclopedia.com. (November 14, 2018). https://www.encyclopedia.com/medicine/news-wires-white-papers-and-books/hypothermia

"Hypothermia." UXL Complete Health Resource. . Retrieved November 14, 2018 from Encyclopedia.com: https://www.encyclopedia.com/medicine/news-wires-white-papers-and-books/hypothermia

Learn more about citation styles

Citation styles

Encyclopedia.com gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).

Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

http://www.mla.org/style

The Chicago Manual of Style

http://www.chicagomanualofstyle.org/tools_citationguide.html

American Psychological Association

http://apastyle.apa.org/

Notes:
  • Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most Encyclopedia.com content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
  • In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.

hypothermia

hypothermia (hy-poh-therm-iă) n.
1. accidental reduction of body temperature below the normal range. It is particularly liable to occur in babies and the elderly.

2. deliberate lowering of body temperature for therapeutic purposes. This may be done during surgery, in order to reduce the patient's requirement for oxygen.

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"hypothermia." A Dictionary of Nursing. . Encyclopedia.com. 14 Nov. 2018 <https://www.encyclopedia.com>.

"hypothermia." A Dictionary of Nursing. . Encyclopedia.com. (November 14, 2018). https://www.encyclopedia.com/caregiving/dictionaries-thesauruses-pictures-and-press-releases/hypothermia

"hypothermia." A Dictionary of Nursing. . Retrieved November 14, 2018 from Encyclopedia.com: https://www.encyclopedia.com/caregiving/dictionaries-thesauruses-pictures-and-press-releases/hypothermia

Learn more about citation styles

Citation styles

Encyclopedia.com gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).

Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

http://www.mla.org/style

The Chicago Manual of Style

http://www.chicagomanualofstyle.org/tools_citationguide.html

American Psychological Association

http://apastyle.apa.org/

Notes:
  • Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most Encyclopedia.com content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
  • In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.

hypothermia

hypothermia Low body temperature (normal is around 37 °C). Occurs among elderly people far more readily than in younger adults, often with fatal results. Also used in connection with deliberate reduction of body temperature to 28 °C to permit heart and brain surgery.

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"hypothermia." A Dictionary of Food and Nutrition. . Encyclopedia.com. 14 Nov. 2018 <https://www.encyclopedia.com>.

"hypothermia." A Dictionary of Food and Nutrition. . Encyclopedia.com. (November 14, 2018). https://www.encyclopedia.com/education/dictionaries-thesauruses-pictures-and-press-releases/hypothermia

"hypothermia." A Dictionary of Food and Nutrition. . Retrieved November 14, 2018 from Encyclopedia.com: https://www.encyclopedia.com/education/dictionaries-thesauruses-pictures-and-press-releases/hypothermia

Learn more about citation styles

Citation styles

Encyclopedia.com gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).

Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

http://www.mla.org/style

The Chicago Manual of Style

http://www.chicagomanualofstyle.org/tools_citationguide.html

American Psychological Association

http://apastyle.apa.org/

Notes:
  • Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most Encyclopedia.com content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
  • In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.

hypothermia

hypothermia Fall in body temperature to below 35°C. Most at risk are newborns and the elderly. Insidious in onset, it can progress to coma and death. Hypothermia is sometimes induced during surgery to lower the body's oxygen demand. It occurs naturally in animals during hibernation.

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"hypothermia." World Encyclopedia. . Encyclopedia.com. 14 Nov. 2018 <https://www.encyclopedia.com>.

"hypothermia." World Encyclopedia. . Encyclopedia.com. (November 14, 2018). https://www.encyclopedia.com/environment/encyclopedias-almanacs-transcripts-and-maps/hypothermia

"hypothermia." World Encyclopedia. . Retrieved November 14, 2018 from Encyclopedia.com: https://www.encyclopedia.com/environment/encyclopedias-almanacs-transcripts-and-maps/hypothermia

Learn more about citation styles

Citation styles

Encyclopedia.com gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).

Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

http://www.mla.org/style

The Chicago Manual of Style

http://www.chicagomanualofstyle.org/tools_citationguide.html

American Psychological Association

http://apastyle.apa.org/

Notes:
  • Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most Encyclopedia.com content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
  • In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.

hypothermia

hy·po·ther·mi·a / ˌhīpəˈ[unvoicedth]ərmēə/ • n. the condition of having an abnormally low body temperature, typically one that is dangerously low.

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"hypothermia." The Oxford Pocket Dictionary of Current English. . Encyclopedia.com. 14 Nov. 2018 <https://www.encyclopedia.com>.

"hypothermia." The Oxford Pocket Dictionary of Current English. . Encyclopedia.com. (November 14, 2018). https://www.encyclopedia.com/humanities/dictionaries-thesauruses-pictures-and-press-releases/hypothermia-0

"hypothermia." The Oxford Pocket Dictionary of Current English. . Retrieved November 14, 2018 from Encyclopedia.com: https://www.encyclopedia.com/humanities/dictionaries-thesauruses-pictures-and-press-releases/hypothermia-0

Learn more about citation styles

Citation styles

Encyclopedia.com gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).

Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

http://www.mla.org/style

The Chicago Manual of Style

http://www.chicagomanualofstyle.org/tools_citationguide.html

American Psychological Association

http://apastyle.apa.org/

Notes:
  • Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most Encyclopedia.com content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
  • In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.

hypothermia

hypothermia •Grasmere • cashmere •Emyr, premier •macadamia, Mesopotamia •academia, anaemia (US anemia), Bohemia, Euphemia, hypoglycaemia, leukaemia (US leukemia), septicaemia (US septicemia), uraemia •bulimia, Ymir •arrhythmia • Vladimir • encomia •costumier • Windermere •Hermia, hyperthermia, hypothermia

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"hypothermia." Oxford Dictionary of Rhymes. . Encyclopedia.com. 14 Nov. 2018 <https://www.encyclopedia.com>.

"hypothermia." Oxford Dictionary of Rhymes. . Encyclopedia.com. (November 14, 2018). https://www.encyclopedia.com/humanities/dictionaries-thesauruses-pictures-and-press-releases/hypothermia

"hypothermia." Oxford Dictionary of Rhymes. . Retrieved November 14, 2018 from Encyclopedia.com: https://www.encyclopedia.com/humanities/dictionaries-thesauruses-pictures-and-press-releases/hypothermia

Learn more about citation styles

Citation styles

Encyclopedia.com gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).

Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

http://www.mla.org/style

The Chicago Manual of Style

http://www.chicagomanualofstyle.org/tools_citationguide.html

American Psychological Association

http://apastyle.apa.org/

Notes:
  • Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most Encyclopedia.com content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
  • In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.

Hypothermia

Hypothermia

Intentional hypothermia

Accidental hypothermia

Primary and secondary hypothermia

Resources

Hypothermia is the intentional or accidental reduction of core body temperature to below 95°F (35°C) which, in severe instances, is fatal. Because humans are endothermicwarm-blooded creatures producing their own body heatthe core body temperature remains relatively constant at 98.6°F (37°C), even in fluctuating environmental temperatures. However, in extreme conditions, a healthy, physically fit persons core body temperature can rise considerably above this norm and cause heatstroke or fall below it far enough to cause hypothermia. Elderly people, for instance, have succumbed to hypothermia after prolonged exposure to indoor air temperatures of 50 to 65°F (10.0 to 18.3°C). Between 1979 and 2005, deaths from hypothermia in the United States has ranged from about 400 to about 1,100 annually.

Intentional hypothermia

Intentional hypothermia is used in medicine in both regional and total-body cooling for organ and tissue protection, preservation, or destruction. Interrupted blood flow starves organs of oxygen and may cause permanent organ damage or death. The bodys metabolic rate (the rate at which cells provide energy for the bodys vital functioning) decreases 8% with each 1.8°F (1°C) reduction in core body temperature, thus requiring reduced amounts of oxygen. Total-body hypothermia lowers the body temperature and slows the metabolic rate, protecting organs from reduced oxygen supply during the interruption of blood flow necessary in certain surgical procedures. In some procedures, like heart repair and organ transplantation, individual organs are preserved by intentional hypothermia of the organ involved. In open-heart surgery, blood supply to the chilled heart can be totally interrupted while the surgeon repairs the damaged organ. Organ and tissue destruction using extreme hypothermia -212 to -374°F (-100 to -190°C) is utilized in retinal and glaucoma surgery and to destroy pre-cancerous cells in some body tissue. This is called cryosurgery.

History of medical use of intentional hypothermia

Intentional hypothermia is not a modern phenomenon. With it, ancient Egyptians treated high fevers; as did Hipparchus (c. 166-125 BC)who also understood its analgesic (pain-killing) properties; the Romans; and Europeans of the Middle Ages. Napoleons surgeon general used cryoanalgesia when performing amputations. He discovered that packing a limb in ice and snow not only killed most of the pain, it also helped prevent bleeding. Today, intentional hypothermia is most commonly used in heart surgery.

Accidental hypothermia

Accidental hypothermia is potentially fatal. It can happen as simply as falling off a log. Falling into icy water, or exposure to cold weather without appropriate protective clothing, can quickly result in death. Hypothermia is classified into four states. In mild cases of 95 to 89.6°F (35 to 32°C), symptoms include feeling cold, shivering (which helps raise body temperature), increased heart rate, desire to urinate, and some loss of coordination. Moderate 87.8 to 78.8°F (31 to 26°C) hypothermia causes a decrease in, or cessation of, shivering; weakness; sleepiness; confusion; slurred speech; and lack of coordination. Deep hypothermia 77 to 68°F (25 to 20°C) is extremely dangerous as the body can no longer produce heat. Sufferers may behave irrationally, become comatose, lose the ability to see, and often cannot follow commands. In profound cases 66 to 57°F (19 to 14°C), the sufferer will become rigid and may even appear dead, with dilated pupils, extremely low blood pressure, and barely perceptible heartbeat and breathing. This state usually requires complete, professional cardiopulmonary resuscitation for survival.

Primary and secondary hypothermia

Hypothermia is also divided into two types: primary and secondary. Primary hypothermia occurs when the bodys heat-balancing mechanisms are working properly but are subjected to extreme cold, such as exposure to cold air or cold water. Hypothermia due to cold air usually takes at least several hours to develop, but immersion hypothermia will occur within about an hour of entering the water because water draws heat away from the body much faster than air does. Secondary hypothermia affects people whose heat-balancing mechanisms are impaired in some way and, thus, cannot respond adequately to moderate or perhaps even mild cold. Among the reasons for the failure of the bodys heat-balancing are diabetes, malnutrition, bacterial infection, thyroid disease, and the use of medications and other substances that affect the brain or spinal cord, such as alcohol.

Secondary hypothermia is often a threat to the elderly, who may be on medications or suffering from illnesses that affect their ability to conserve heat. Malnutrition and immobility can also put the elderly at risk. Some medical research also suggests that shivering and blood vessel narrowing (two of the bodys defenses against cold) may not be triggered as quickly in older people. For these and other reasons, the elderly can, over a period of days or even weeks, fall victim to hypothermia in poorly insulated homes or other surroundings. In addition, hypothermia can easily be misdiagnosed as a stroke or some other common illness of old age.

Causes of accidental hypothermia

Although overexertion in a cold environment causes most accidental hypothermia, it may occur during anesthesia, primarily due to central nervous system depression of the bodys heat-regulating mechanism; and in babies, elderly, and ill people whose homes are inadequately heated. The human body loses heat to the environment through conduction, convection, evaporation and respiration, and radiation. It generates heat through the metabolic process.

Conduction occurs when direct contact is made between the body and a cold object, and heat passes from the body to that object. Convection is when cold air or water makes contact with the body, become warm, and move away to be replaced by more of the same. The cooler the air or water, and the faster it moves, the faster the core body temperature drops.

Evaporation through perspiration and respiration provides almost 30% of the bodys natural cooling mechanism. Because cold air contains little water and readily evaporates perspiration; and because physical exertion produces sweating, even in extreme cold; heat loss through evaporation takes place even at very low temperatures. The dry air that humans inhale attracts moisture from the lining of the nose and throat. This can happen so quickly that, by the time the air reaches the lungs, it is completely saturated. Combined, evaporation and convection from wet clothes will reduce the body temperature dangerously quickly.

KEY TERMS

Cryoanalgesia Using cold as a pain reducing anaesthetic.

Cryosurgery Freezing the tissue to be dissected.

Endothermic Capable of producing body heat.

When the body is warmer than its environment, it radiates heat into that environment. Radiation is the greatest source of heat loss, and the colder the environment, the greater the potential for heat loss. Most clothing is of little help because body heat radiates into clothing and from clothing into the atmosphere or object with which it comes into contact.

Preventing accidental hypothermia

Although profound hypothermia can be reversed in some instances, even mild states can quickly lead to death. However, through knowledge and common sense, hypothermia is avoidable. Two factors essential in preventing accidental hypothermia are reducing loss of body heat and increasing body heat production.

Appropriate clothing, shelter, and diet are all essential. Apart from new, synthetic fabrics that allow undergarments to wick perspiration away from the body while remaining dry and warm, and outer garments that breathe while keeping wind and moisture out, natural wool fibers contain millions of air pockets that act as excellent insulators. Even when saturated, wool maintains 80% of its dry insulation value. Because it provides no insulation and becomes extremely cold when wet, cotton is often called killer cotton by experienced outdoors people. As 60% of body heat is lost by radiation from the head, hats can be lifesavers. Fingers, toes, hands, and feet lose heat quickly, and excellent quality boots, gloves, and mittens are a must.

Regular consumption of high-energy food rich in carbohydrates aids the body in heat production, while 13 to 17 c (3 to 4 L) of water a day prevents rapid dehydration from evaporation. Exercising large muscleslike those in the legsis the best generator of body heat; however, overexertion must be avoided as it will only speed the onset of hypothermia.

Resources

BOOKS

Blumberg, Mark Samuel. Body Heat: Temperture and Life on Earth. Cambridge, MA: Harvard University Press, 2002.

Jessen, Claus. Temperature Regulation in Humans and Other Mammals. Berlin, Germany, and New York: Springer, 2001.

Mayer, Stephan, and Daniel I. Sessler, eds. Therapeutic Hypothermia. New York: Marcel Dekker, 2005.

Marie L. Thompson

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"Hypothermia." The Gale Encyclopedia of Science. . Encyclopedia.com. 14 Nov. 2018 <https://www.encyclopedia.com>.

"Hypothermia." The Gale Encyclopedia of Science. . Encyclopedia.com. (November 14, 2018). https://www.encyclopedia.com/science/encyclopedias-almanacs-transcripts-and-maps/hypothermia-0

"Hypothermia." The Gale Encyclopedia of Science. . Retrieved November 14, 2018 from Encyclopedia.com: https://www.encyclopedia.com/science/encyclopedias-almanacs-transcripts-and-maps/hypothermia-0

Learn more about citation styles

Citation styles

Encyclopedia.com gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).

Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

http://www.mla.org/style

The Chicago Manual of Style

http://www.chicagomanualofstyle.org/tools_citationguide.html

American Psychological Association

http://apastyle.apa.org/

Notes:
  • Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most Encyclopedia.com content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
  • In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.

Hypothermia

Hypothermia

Hypothermia is the intentional or accidental reduction of core body temperature to below 95°F (35°C) which, in severe instances, is fatal. Because humans are endothermic—warm-blooded creatures producing our own body heat—our core body temperature remains relatively constant at 98.6°F (37°C), even in fluctuating environmental temperatures. However, in extreme conditions, a healthy, physically fit person's core body temperature can rise considerably above this norm and cause heat stroke or fall below it far enough to cause hypothermia.


Intentional hypothermia

Intentional hypothermia is used in medicine in both regional and total-body cooling for organ and tissue protection, preservation, or destruction. Interrupted blood flow starves organs of oxygen and may cause permanent organ damage or death. The body's metabolic rate (the rate at which cells provide energy for the body's vital functioning) decreases 8% with each 1.8°F (1°C) reduction in core body temperature, thus requiring reduced amounts of oxygen. Total-body hypothermia lowers the body temperature and slows the metabolic rate, protecting organs from reduced oxygen supply during the interruption of blood flow necessary in certain surgical procedures. In some procedures, like heart repair and organ transplantation, individual organs are preserved by intentional hypothermia of the organ involved. In open heart surgery , blood supply to the chilled heart can be totally interrupted while the surgeon repairs the damaged organ. Organ and tissue destruction using extreme hypothermia - 212 to -374°F (-100 to -190°C) is utilized in retinal and glaucoma surgery and to destroy pre-cancerous cells in some body tissue. This is called cryosurgery.

History of medical use of intentional hypothermia

Intentional hypothermia is not a modern phenomenon. With it, ancient Egyptians treated high fevers; as did Hippocrates—who also understood its analgesic (pain-killing) properties; the Romans; and Europeans of the Middle Ages. Napoleon's surgeon general used cryoanalgesia when performing amputations. He discovered that packing a limb in ice and snow not only killed most of the pain , it also helped prevent bleeding. Today, intentional hypothermia is most commonly used in heart surgery.


Accidental hypothermia

Accidental hypothermia is potentially fatal. It can happen as simply as falling off a log. Falling into icy water , or exposure to cold weather without appropriate protective clothing, can quickly result in death. Hypothermia is classified into four states. In mild cases 95–89.6°F (35–32°C), symptoms include feeling cold, shivering (which helps raise body temperature), increased heart rate and desire to urinate, and some loss of coordination. Moderate 87.8–78.8°F (31–26°C) hypothermia causes a decrease in, or cessation of, shivering; weakness; sleepiness; confusion; slurred speech ; and lack of coordination. Deep hypothermia 77–68°F (25–20°C) is extremely dangerous as the body can no longer produce heat. Sufferers may behave irrationally, become comatose, lose the ability to see, and often cannot follow commands. In profound cases 66–57°F (19–14°C), the sufferer will become rigid and may even appear dead, with dilated pupils, extremely low blood pressure , and barely perceptible heartbeat and breathing. This state usually requires complete, professional cardiopulmonary resuscitation for survival.


Causes of accidental hypothermia

Although overexertion in a cold environment causes most accidental hypothermia, it may occur during anesthesia , primarily due to central nervous system depression of the body's heat-regulating mechanism; and in babies, elderly, and ill people whose homes are inadequately heated. The human body loses heat to the environment through conduction, convection , evaporation and respiration , and radiation . It generates heat through the metabolic process.

Conduction occurs when direct contact is made between the body and a cold object, and heat passes from the body to that object. Convection is when cold air or water make contact with the body, become warm, and move away to be replaced by more of the same. The cooler the air or water, and the faster it moves, the faster the core body temperature drops.

Evaporation through perspiration and respiration provides almost 30% of the body's natural cooling mechanism. Because cold air contains little water and readily evaporates perspiration; and because physical exertion produces sweating, even in extreme cold; heat loss through evaporation takes place even at very low temperatures. The dry air we inhale attracts moisture from the lining of our nose and throat so quickly that, by the time the air reaches our lungs, it is completely saturated. Combined, evaporation and convection from wet clothes will reduce the body temperature dangerously quickly.

When the body is warmer than its environment, it radiates heat into that environment. Radiation is the greatest source of heat loss, and the colder the environment, the greater the potential for heat loss. Most clothing is of little help because body heat radiates into clothing and from clothing into the atmosphere or object with which it comes into contact.


Preventing accidental hypothermia

Although profound hypothermia can be reversed in some instances, even mild states can quickly lead to death. However, through knowledge and common sense, hypothermia is avoidable. Two factors essential in preventing accidental hypothermia are reducing loss of body heat and increasing body heat production.

Appropriate clothing, shelter, and diet are all essential. Apart from new, synthetic fabrics which allow undergarments to "wick" perspiration away from the body while remaining dry and warm, and outergarments which "breathe" while keeping wind and moisture out, natural wool fibers contain millions of air pockets which act as excellent insulators. Even when saturated, wool maintains 80% of its dry insulation value. Because it provides no insulation and becomes extremely cold when wet, cotton is often called "killer cotton" by experienced outdoors people. As 60% of body heat is lost by radiation from the head, hats can be lifesavers. Fingers, toes, hands, and feet lose heat quickly, and excellent quality boots, gloves, and mittens are a must.

Regular consumption of high-energy food rich in carbohydrates aids the body in heat production, while 13-17 c (3-4L) of water a day prevents rapid dehydration from evaporation. Exercising large muscles-like those in the legs—is the best generator of body heat; however, overexertion must be avoided as it will only speed the onset of hypothermia.


Resources

books

Auerbach, Paul S. Medicine for the Outdoors: A Guide to Emergency Medical Procedures and First Aid. U.S.A./Canada: Little, Brown & Company, Limited.

Schönbaum, E., and Peter Lomax, ed. Thermoregulation: Pathology, Pharmacology, and Therapy.

Wilkerson, James A. Hypothermia, Frostbite, and Other Cold Injuries. Vancouver: Douglas & McIntyre, Ltd., 1986.


Marie L. Thompson

KEY TERMS

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Cryoanalgesia

—Using cold as a pain reducing anaesthetic.

Cryosurgery

—Freezing the tissue to be dissected.

Endothermic

—Capable of producing body heat.

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"Hypothermia." The Gale Encyclopedia of Science. . Encyclopedia.com. 14 Nov. 2018 <https://www.encyclopedia.com>.

"Hypothermia." The Gale Encyclopedia of Science. . Encyclopedia.com. (November 14, 2018). https://www.encyclopedia.com/science/encyclopedias-almanacs-transcripts-and-maps/hypothermia-1

"Hypothermia." The Gale Encyclopedia of Science. . Retrieved November 14, 2018 from Encyclopedia.com: https://www.encyclopedia.com/science/encyclopedias-almanacs-transcripts-and-maps/hypothermia-1

Learn more about citation styles

Citation styles

Encyclopedia.com gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).

Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

http://www.mla.org/style

The Chicago Manual of Style

http://www.chicagomanualofstyle.org/tools_citationguide.html

American Psychological Association

http://apastyle.apa.org/

Notes:
  • Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most Encyclopedia.com content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
  • In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.

Hypothermia

Hypothermia

Hypothermia is the physical state in which the core temperature of the body is significantly below its healthy norm of 98.6°F (37°C). Hypothermia is a condition that is the opposite of hyperthermia, the excessively elevated temperature present in an overheated body. Hypothermia most typically occurs in cold weather circumstances, where the body is inadequately protected from the elements, or where external sources of heat are not available. The ability of the human body to dissipate heat through perspiration and the functions of the cardiovascular system is far better than its ability to retain heat in response to environmental conditions.

Hypothermia is not itself an illness or an injury, but it represents the triggering mechanism for a number of cold-related outcomes, including organ damage and failure of the cardiovascular system. Hypothermia is a separate and unrelated condition to the injury known as frostbite, which is a freezing of the tissue and skin; given the cause of frostbite, hypothermia and frostbite often occur in the same circumstances.

Hypothermia is popularly associated with cold, snowy, and intemperate weather. While such conditions are a background to hypothermic events, this condition can occur where the air temperature is 40°F (4°C) or lower; it is also a common result for sailors, paddlers, or rowers that become soaked in cold water temperatures, either through the spray created by moving boats, or if the athlete is actually immersed in cold water. Athletes that are either waiting to join a competition, such as cross-country runners prior to race start, or football players standing on a sideline, are also vulnerable to hypothermia in some conditions.

The generally recognized risk factors associated with the potential for hypothermia include:

  • Low air temperatures, often combined with inadequate clothing or protection; the reflex action of the body to cold exposure is to shiver, an involuntary effort to generate heat.
  • Wind chill, the combined effect of temperature and wind on the human body; wind chill is a deceptive phenomenon, as it may occur in all types of cold weather environments, including sunshine. As a general proposition, at temperatures below 40°F (4°C), winds at speeds as low as 5 mph (8 km/h) can significantly induce increased sensations of cold; the greater the wind speed, the more pronounced the effect of cold will be.
  • Moisture; skin that is wet, though either excess perspiration or environmental effects, will freeze more readily than dry skin. Moisture will also magnify the effect of wind chill.
  • Consumption of alcohol, which tends to stimulate blood flow in the peripheral parts of the body, an action that contributes to heat loss.
  • Amount of skin exposed to the elements by the athlete; exposed skin permits heat to be lost by both convection and radiation to the immediate environment.
  • Consumption of caffeine or any other diuretic, which acts to reduce fluid volumes in the cardiovascular system.

In its mildest manifestation, hypothermia causes pronounced shivering, numbness, and a cold feeling through out the body. As the body temperature remains low, the symptoms become more pronounced, as the person will experience an inability to move quickly or decisively, accompanied by dizziness and confused thinking. At its most extreme, the affected person will experience a rigidity of the muscles, followed by a lapse into coma. At a body temperature of less than 95°F (35°C), the person must receive immediate attention or, as a result of a progressive decline in the function of the organs and the internal systems, death will result.

Once detected, the management of hypothermia is a straightforward process. The first and most important consideration is the removal of the injured person from the cold environment. It is important that while the person is made warmer, that he or she not be so heated as to induce perspiration, which will result in a reduction of body fluid available to circulate and slowly warm the person. The second treatment step is the removal of any wet clothing and dressing the person with dry clothes, or wrapping the person in a blanket, as wet clothing has very poor thermal qualities. The temptation to rub or otherwise seek to stimulate circulation in the extremities of the hypothermic person should be resisted; such efforts may direct cold blood from the limbs to the heart, causing a sudden shock to that organ. The warming of the hypothermic person is best done gradually.

In outdoor cold weather endurance events, such as cross-country skiing, it is possible for a case of hypothermia to occur at the same time the athlete is experiencing dehydration. The return to normal fluid levels will determine how quickly the thermoregulatory system can resume normal function.

see also Acclimatization; Cold-related illnesses and emergencies; Hydration; Hypothermia; Thermoregulatory system.

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"Hypothermia." World of Sports Science. . Encyclopedia.com. 14 Nov. 2018 <https://www.encyclopedia.com>.

"Hypothermia." World of Sports Science. . Encyclopedia.com. (November 14, 2018). https://www.encyclopedia.com/sports/sports-fitness-recreation-and-leisure-magazines/hypothermia

"Hypothermia." World of Sports Science. . Retrieved November 14, 2018 from Encyclopedia.com: https://www.encyclopedia.com/sports/sports-fitness-recreation-and-leisure-magazines/hypothermia

Learn more about citation styles

Citation styles

Encyclopedia.com gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).

Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

http://www.mla.org/style

The Chicago Manual of Style

http://www.chicagomanualofstyle.org/tools_citationguide.html

American Psychological Association

http://apastyle.apa.org/

Notes:
  • Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most Encyclopedia.com content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
  • In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.