Hypothermia
Encyclopedia
Hypothermia is a condition in which core temperature drops below the required temperature for normal metabolism
and body functions which is defined as 35 °C (95 °F). Body temperature is usually maintained near a constant level of 36.5 – through biologic homeostasis
or thermoregulation
. If exposed to cold and the internal mechanisms are unable to replenish the heat that is being lost, a drop in core temperature occurs. As body temperature decreases, characteristic symptoms occur such as shivering
and mental confusion
.
Hypothermia is the opposite of hyperthermia
which is present in heat exhaustion and heat stroke. One of the lowest documented body temperature from which anyone has recovered was 13 °C (55.4 °F), in a drowning incident involving a 7-year-old girl in Sweden in December 2010.
in adults is 34.4 –. Sometimes a narrower range is stated, such as 36.5 –. Hypothermia is defined as any body temperature below 35 °C (95 °F). It is subdivided into four different degrees, mild 32–35 °C (89.6–95 F); moderate, 28–32 °C (82.4–89.6 F); severe, 20–28 °C (68–82.4 F); and profound at less than 20 °C (68 °F). This is in contrast to hyperthermia
and fever
which are defined as a temperature of greater than 37.5 °C (99.5 °F)-38.3 °C (100.9 °F).
Other cold-related injuries that can either be present alone or in combination with hypothermia include:
, hypertension
, tachycardia
, tachypnea
, and vasoconstriction
). These are all physiological responses to preserve heat. Cold diuresis, mental confusion, as well as hepatic dysfunction
may also be present. Hyperglycemia
may be present, as glucose consumption by cells and insulin secretion both decrease, and tissue sensitivity to insulin may be blunted. Sympathetic
activation also releases glucose from the liver. In many cases, however, especially in alcoholic patients, hypoglycemia appears to be a more common presentation. Hypoglycemia is also found in many hypothermic patients because hypothermia often is a result of hypoglycemia.
Difficulty in speaking, sluggish thinking, and amnesia start to appear; inability to use hands and stumbling is also usually present. Cellular metabolic processes shut down. Below 30 °C (86 °F), the exposed skin becomes blue and puffy, muscle coordination becomes very poor, walking becomes almost impossible, and the person 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
.
Rescuers who are trained in mountain survival techniques are taught to expect this; however, some may assume incorrectly that urban victims of hypothermia have been subjected to a sexual assault.
One explanation for the effect is a cold-induced 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 (known as a loss of vasomotor tone) and relax, leading to a sudden surge of blood (and heat) to the extremities, fooling the person into feeling overheated.
. Any condition that decreases heat production, increases heat loss, or impairs thermoregulation, however, may contribute. Thus, hypothermia risk factors include: any condition that affects judgment (hypoglycemia
), the extremes of age, poor clothing, chronic medical conditions (such as hypothyroidism
and sepsis
), substance abuse, homelessness, and living in a cold environment. Hypothermia also occurs frequently in major trauma. Hypothermia also is observed in severe cases of anorexia nervosa.
consumption increases the risk of hypothermia via its action as a vasodilator. It increases blood flow to the body's skin and extremities, making a person feel warm, while increasing heat loss. Between 33 to 73% of cases of hypothermia are complicated by alcohol.
in cold water. The limitation of finger dexterity due to pain or numbness decreases general safety and work capacity, which consequently increases the risk of other injuries. Due to the use of gas mixtures containing helium at extreme depths, the use of argon inflation for dry suits, or hot water suits become a necessity for diving deep in colder waters.
Other predisposing factors leading to immersion hypothermia include dehydration
, inadequate rewarming with repetitive diving, starting a dive while wearing cold, wet dry suit
undergarments, sweating with work, inadequate thermal insulation
(for example, thin dry suit undergarment), and poor physical conditioning
.
Heat is lost more quickly in water than on land. Water temperatures that would be quite reasonable as outdoor air temperatures can lead to hypothermia. A water temperature of 10 °C (50 °F) often leads to death in one hour, and water temperatures hovering at freezing can lead to death in as little as 15 minutes. Water at a temperature of 26 °C (78.8 °F) will, after prolonged exposure, lead to hypothermia.
, and in the liver
, while it is lost through the skin (90%) and lungs (10%). Heat production may be increased 2 to 4 fold through muscle contractions ( i.e. exercise and shivering ). Rates of bodily heat loss are determined, as with any object, by convection
, conduction, and radiation
. The rates of these can be affected by clothing and other environmental conditions.
Many changes to physiology occur as body temperature decreases. These occur in the cardiovascular system leading to the Osborn J wave
and other dysrhythmias, decreased CNS
electrical activity, cold diuresis, and non-cardiogenic pulmonary edema.
. Also, ventricular fibrillation
frequently occurs at <28°C (82.4°F) and asystole
at <20°C (68°F). The Osborn J may look very similar to those of an acute ST elevation myocardial infarction. Thrombolysis as a reaction to the presence of Osborn J waves is not indicated, as it would only worsen the underlying coagulopathy
caused by hypothermia.
As a hypothermic person's heart rate may be very slow, prolonged palpation could be required before detecting a pulse. In 2005 American Heart Association
recommended at least 30 – 45 seconds to verify the absence of a pulse before initiating CPR.
Most physicians are recommended not to declare a patient dead until their body is warmed to a normal body temperature, since extreme hypothermia can suppress heart and brain function.
and wool
fabrics are superior to cotton as they provide better insulation when wet and dry. Some synthetic fabrics, such as polypropylene and polyester, are used in clothing designed to wick perspiration away from the body, such as liner socks and moisture-wicking undergarments.
The United States Coast Guard
promotes using life vests as a method of protection against hypothermia through the 50/50/50 rule: If someone is in 50 °F (10 °C) water for 50 minutes, he/she has a 50 percent better chance of survival if wearing a life jacket. A heat escape lessening position
can be used to increase survival in cold water.
Aggressiveness of treatment is matched to the degree of hypothermia. Treatment ranges from noninvasive, passive external warming, to active external rewarming, to active core rewarming. In severe cases resuscitation begins with simultaneous removal from the cold environment and concurrent management of the airway, breathing, and circulation. Rapid rewarming is then commenced. A minimum of patient movement is recommended as aggressive handling may increase risks of a dysrhythmia
.
Hypoglycemia
is a frequent complication of hypothermia, and therefore needs to be tested for and treated. Intravenous thiamine
and glucose
is often recommended as many causes of hypothermia are complicated by Wernicke's encephalopathy
.
in both armpits and groin. It is recommended for moderate hypothermia. Active core rewarming involves the use of intravenous warmed fluids, irrigation of body cavities with warmed fluids (the thorax, peritoneal, stomach, or bladder), use of warm humidified inhaled air, or use of extracorporeal
rewarming such as via a heart lung machine. Extracorporeal rewarming is the fastest method for those with severe hypothermia.
in combination with a low cardiac output
which may occur during active treatment of a severely hypothermic person. There is theoretical concern that external rewarming rather than internal rewarming may increase the risk. However, recent studies have not supported these concerns.
accidents in water near 0°C (32°F) can be revived over an hour after losing consciousness. The cold water lowers metabolism
, allowing the brain to withstand a much longer period of hypoxia
. While survival is possible, mortality
from severe or profound hypothermia remains high despite optimal treatment. Studies estimate mortality at between 38% – 75%. If there are obvious fatal injuries or the chest is too frozen, compression resuscitation is futile.
Hypothermia has played a major role in the success or failure of many military campaigns from Hannibal's loss of nearly half his men in 218 B.C. to the near destruction of Napoleon's armies in Russia
in 1812. Loss of life to hypothermia continued through the first and second world wars, especially in the Battle of Stalingrad. Civilian examples of deaths caused by hypothermia are found during the sinkings of the RMS Titanic and RMS Lusitania
.
or torpor
.
Water bears (Tardigrade
), microscopic multicellular organisms, can survive freezing
at low temperatures by replacing most of their internal water with the sugar
trehalose
, preventing it from crystallization that otherwise damage cell membranes.
Metabolism
Metabolism is the set of chemical reactions that happen in the cells of living organisms to sustain life. These processes allow organisms to grow and reproduce, maintain their structures, and respond to their environments. Metabolism is usually divided into two categories...
and body functions which is defined as 35 °C (95 °F). Body temperature is usually maintained near a constant level of 36.5 – through biologic homeostasis
Homeostasis
Homeostasis is the property of a system that regulates its internal environment and tends to maintain a stable, constant condition of properties like temperature or pH...
or thermoregulation
Thermoregulation
Thermoregulation is the ability of an organism to keep its body temperature within certain boundaries, even when the surrounding temperature is very different...
. If exposed to cold and the internal mechanisms are unable to replenish the heat that is being lost, a drop in core temperature occurs. As body temperature decreases, characteristic symptoms occur such as shivering
Shivering
Shivering is a bodily function in response to early hypothermia in warm-blooded animals. When the core body temperature drops, the shivering reflex is triggered to maintain homeostasis. Muscle groups around the vital organs begin to shake in small movements in an attempt to create warmth by...
and mental confusion
Mental confusion
Confusion of a pathological degree usually refers to loss of orientation sometimes accompanied by disordered consciousness and often memory Confusion (from Latin confusĭo, -ōnis, noun of action from confundere "to pour together", also "to confuse") of a pathological degree usually refers to loss...
.
Hypothermia is the opposite of hyperthermia
Hyperthermia
Hyperthermia is an elevated body temperature due to failed thermoregulation. Hyperthermia occurs when the body produces or absorbs more heat than it can dissipate...
which is present in heat exhaustion and heat stroke. One of the lowest documented body temperature from which anyone has recovered was 13 °C (55.4 °F), in a drowning incident involving a 7-year-old girl in Sweden in December 2010.
Classification
Normal human body temperatureNormal human body temperature
Normal human body temperature, also known as normothermia or euthermia, is a concept that depends upon the place in the body at which the measurement is made, and the time of day and level of activity of the person...
in adults is 34.4 –. Sometimes a narrower range is stated, such as 36.5 –. Hypothermia is defined as any body temperature below 35 °C (95 °F). It is subdivided into four different degrees, mild 32–35 °C (89.6–95 F); moderate, 28–32 °C (82.4–89.6 F); severe, 20–28 °C (68–82.4 F); and profound at less than 20 °C (68 °F). This is in contrast to hyperthermia
Hyperthermia
Hyperthermia is an elevated body temperature due to failed thermoregulation. Hyperthermia occurs when the body produces or absorbs more heat than it can dissipate...
and fever
Fever
Fever is a common medical sign characterized by an elevation of temperature above the normal range of due to an increase in the body temperature regulatory set-point. This increase in set-point triggers increased muscle tone and shivering.As a person's temperature increases, there is, in...
which are defined as a temperature of greater than 37.5 °C (99.5 °F)-38.3 °C (100.9 °F).
Other cold-related injuries that can either be present alone or in combination with hypothermia include:
- Chilblains are superficial ulcers of the skin that occur when a predisposed individual is repeatedly exposed to cold.
- FrostbiteFrostbiteFrostbite is the medical condition where localized damage is caused to skin and other tissues due to extreme cold. Frostbite is most likely to happen in body parts farthest from the heart and those with large exposed areas...
involves the freezing and destruction of tissue. - Frostnip is a superficial cooling of tissues without cellular destruction.
- Trench footTrench footTrench foot is a medical condition caused by prolonged exposure of the feet to damp, unsanitary, and cold conditions. It is one of many immersion foot syndromes...
or immersion foot is due to repetitive exposure to wet, non-freezing temperatures.
Signs and symptoms
The signs and symptoms vary depending on the degree of hypothermia and may be divided by the three stages of severity.Mild
Symptoms of mild hypothermia may be vague with sympathetic nervous system excitation (shiveringShivering
Shivering is a bodily function in response to early hypothermia in warm-blooded animals. When the core body temperature drops, the shivering reflex is triggered to maintain homeostasis. Muscle groups around the vital organs begin to shake in small movements in an attempt to create warmth by...
, hypertension
Hypertension
Hypertension or high blood pressure is a cardiac chronic medical condition in which the systemic arterial blood pressure is elevated. What that means is that the heart is having to work harder than it should to pump the blood around the body. Blood pressure involves two measurements, systolic and...
, tachycardia
Tachycardia
Tachycardia comes from the Greek words tachys and kardia . Tachycardia typically refers to a heart rate that exceeds the normal range for a resting heart rate...
, tachypnea
Tachypnea
Tachypnea means rapid breathing. Any rate between 12-20 breaths per minute is normal. Tachypnea is a respiration rate greater than 20 breaths per minute. - Distinction from other breathing terms :...
, and vasoconstriction
Vasoconstriction
Vasoconstriction is the narrowing of the blood vessels resulting from contraction of the muscular wall of the vessels, particularly the large arteries, small arterioles and veins. The process is the opposite of vasodilation, the widening of blood vessels. The process is particularly important in...
). These are all physiological responses to preserve heat. Cold diuresis, mental confusion, as well as hepatic dysfunction
Liver disease
Liver disease is a broad term describing any single number of diseases affecting the liver.-Diseases:* Hepatitis, inflammation of the liver, caused mainly by various viruses but also by some poisons , autoimmunity or hereditary conditions...
may also be present. Hyperglycemia
Hyperglycemia
Hyperglycemia or Hyperglycæmia, or high blood sugar, is a condition in which an excessive amount of glucose circulates in the blood plasma. This is generally a glucose level higher than 13.5mmol/l , but symptoms may not start to become noticeable until even higher values such as 15-20 mmol/l...
may be present, as glucose consumption by cells and insulin secretion both decrease, and tissue sensitivity to insulin may be blunted. Sympathetic
Sympathetic nervous system
The sympathetic nervous system is one of the three parts of the autonomic nervous system, along with the enteric and parasympathetic systems. Its general action is to mobilize the body's nervous system fight-or-flight response...
activation also releases glucose from the liver. In many cases, however, especially in alcoholic patients, hypoglycemia appears to be a more common presentation. Hypoglycemia is also found in many hypothermic patients because hypothermia often is a result of hypoglycemia.
Moderate
Low body temperature results in shivering becoming 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.Severe
As the temperature decreases further physiological systems falter and heart rate, respiratory rate, and blood pressure all decreases. This results in an expected HR in the 30s with a temperature of 28 °C (82.4 °F).Difficulty in speaking, sluggish thinking, and amnesia start to appear; inability to use hands and stumbling is also usually present. Cellular metabolic processes shut down. Below 30 °C (86 °F), the exposed skin becomes blue and puffy, muscle coordination becomes very poor, walking becomes almost impossible, and the person exhibits incoherent/irrational behavior including terminal burrowing or even a stupor
Stupor
Stupor is the lack of critical cognitive function and level of consciousness wherein a sufferer is almost entirely unresponsive and only responds to base stimuli such as pain. This is often mistaken for delirium and treated with Haldol and or other anti-psychotic drugs...
. Pulse
Pulse
In medicine, one's pulse represents the tactile arterial palpation of the heartbeat by trained fingertips. The pulse may be palpated in any place that allows an artery to be compressed against a bone, such as at the neck , at the wrist , behind the knee , on the inside of the elbow , and near the...
and respiration
Respiration (physiology)
'In physiology, respiration is defined as the transport of oxygen from the outside air to the cells within tissues, and the transport of carbon dioxide in the opposite direction...
rates decrease significantly, but fast heart rates (ventricular tachycardia, atrial fibrillation) can occur. Major organs fail. Clinical death
Clinical death
Clinical death is the medical term for cessation of blood circulation and breathing, the two necessary criteria to sustain life. It occurs when the heart stops beating in a regular rhythm, a condition called cardiac arrest. The term is also sometimes used in resuscitation research.Stopped blood...
occurs. Because of decreased cellular activity in stage 3 hypothermia, the body will actually take longer to undergo brain death
Brain death
Brain death is the irreversible end of all brain activity due to total necrosis of the cerebral neurons following loss of brain oxygenation. It should not be confused with a persistent vegetative state...
.
Paradoxical undressing
Twenty to fifty percent of hypothermia deaths are associated with paradoxical undressing. This typically occurs during moderate to severe hypothermia, as the person becomes disoriented, confused, and combative. They may begin discarding their clothing, which, in turn, increases the rate of heat loss.Rescuers who are trained in mountain survival techniques are taught to expect this; however, some may assume incorrectly that urban victims of hypothermia have been subjected to a sexual assault.
One explanation for the effect is a cold-induced malfunction of the hypothalamus
Hypothalamus
The Hypothalamus is a portion of the brain that contains a number of small nuclei with a variety of functions...
, the part of the brain that regulates body temperature. Another explanation is that the muscles contracting peripheral blood vessels become exhausted (known as a loss of vasomotor tone) and relax, leading to a sudden surge of blood (and heat) to the extremities, fooling the person into feeling overheated.
Terminal burrowing
Terminal burrowing, also known as hide-and-die syndrome occurs in the final stages of hypothermia, the brain stem produces a burrowing-like behavior, similar to hibernation behavior in animals, such that those with severe hypothermia are often found in small, enclosed spaces, such as under the bed or behind wardrobes.Causes
Hypothermia usually occurs from exposure to low temperatures, and is frequently complicated by alcoholAlcohol
In chemistry, an alcohol is an organic compound in which the hydroxy functional group is bound to a carbon atom. In particular, this carbon center should be saturated, having single bonds to three other atoms....
. Any condition that decreases heat production, increases heat loss, or impairs thermoregulation, however, may contribute. Thus, hypothermia risk factors include: any condition that affects judgment (hypoglycemia
Hypoglycemia
Hypoglycemia or hypoglycæmia is the medical term for a state produced by a lower than normal level of blood glucose. The term literally means "under-sweet blood"...
), the extremes of age, poor clothing, chronic medical conditions (such as hypothyroidism
Hypothyroidism
Hypothyroidism is a condition in which the thyroid gland does not make enough thyroid hormone.Iodine deficiency is the most common cause of hypothyroidism worldwide but it can be caused by other causes such as several conditions of the thyroid gland or, less commonly, the pituitary gland or...
and sepsis
Sepsis
Sepsis is a potentially deadly medical condition that is characterized by a whole-body inflammatory state and the presence of a known or suspected infection. The body may develop this inflammatory response by the immune system to microbes in the blood, urine, lungs, skin, or other tissues...
), substance abuse, homelessness, and living in a cold environment. Hypothermia also occurs frequently in major trauma. Hypothermia also is observed in severe cases of anorexia nervosa.
Alcohol
AlcoholAlcohol
In chemistry, an alcohol is an organic compound in which the hydroxy functional group is bound to a carbon atom. In particular, this carbon center should be saturated, having single bonds to three other atoms....
consumption increases the risk of hypothermia via its action as a vasodilator. It increases blood flow to the body's skin and extremities, making a person feel warm, while increasing heat loss. Between 33 to 73% of cases of hypothermia are complicated by alcohol.
Water
Hypothermia continues to be a major limitation to divingUnderwater diving
Underwater diving is the practice of going underwater, either with breathing apparatus or by breath-holding .Recreational diving is a popular activity...
in cold water. The limitation of finger dexterity due to pain or numbness decreases general safety and work capacity, which consequently increases the risk of other injuries. Due to the use of gas mixtures containing helium at extreme depths, the use of argon inflation for dry suits, or hot water suits become a necessity for diving deep in colder waters.
Other predisposing factors leading to immersion hypothermia include dehydration
Dehydration
In physiology and medicine, dehydration is defined as the excessive loss of body fluid. It is literally the removal of water from an object; however, in physiological terms, it entails a deficiency of fluid within an organism...
, inadequate rewarming with repetitive diving, starting a dive while wearing cold, wet dry suit
Dry suit
A dry suit or drysuit provides thermal insulation or passive thermal protection to the wearer while immersed in water, and is worn by divers, boaters, water sports enthusiasts, and others who work or play in or near cold water. A dry suit normally protects the whole body except the head, hands, and...
undergarments, sweating with work, inadequate thermal insulation
Thermal insulation
Thermal insulation is the reduction of the effects of the various processes of heat transfer between objects in thermal contact or in range of radiative influence. Heat transfer is the transfer of thermal energy between objects of differing temperature...
(for example, thin dry suit undergarment), and poor physical conditioning
Physical exercise
Physical exercise is any bodily activity that enhances or maintains physical fitness and overall health and wellness. It is performed for various reasons including strengthening muscles and the cardiovascular system, honing athletic skills, weight loss or maintenance, as well as for the purpose of...
.
Heat is lost more quickly in water than on land. Water temperatures that would be quite reasonable as outdoor air temperatures can lead to hypothermia. A water temperature of 10 °C (50 °F) often leads to death in one hour, and water temperatures hovering at freezing can lead to death in as little as 15 minutes. Water at a temperature of 26 °C (78.8 °F) will, after prolonged exposure, lead to hypothermia.
Pathophysiology
Heat is primarily generated in muscle tissue, including the heartHeart
The heart is a myogenic muscular organ found in all animals with a circulatory system , that is responsible for pumping blood throughout the blood vessels by repeated, rhythmic contractions...
, and in the liver
Liver
The liver is a vital organ present in vertebrates and some other animals. It has a wide range of functions, including detoxification, protein synthesis, and production of biochemicals necessary for digestion...
, while it is lost through the skin (90%) and lungs (10%). Heat production may be increased 2 to 4 fold through muscle contractions ( i.e. exercise and shivering ). Rates of bodily heat loss are determined, as with any object, by convection
Convection
Convection is the movement of molecules within fluids and rheids. It cannot take place in solids, since neither bulk current flows nor significant diffusion can take place in solids....
, conduction, and radiation
Radiation
In physics, radiation is a process in which energetic particles or energetic waves travel through a medium or space. There are two distinct types of radiation; ionizing and non-ionizing...
. The rates of these can be affected by clothing and other environmental conditions.
Many changes to physiology occur as body temperature decreases. These occur in the cardiovascular system leading to the Osborn J wave
Osborn wave
Osborn waves are a electrocardiogram finding....
and other dysrhythmias, decreased CNS
Central nervous system
The central nervous system is the part of the nervous system that integrates the information that it receives from, and coordinates the activity of, all parts of the bodies of bilaterian animals—that is, all multicellular animals except sponges and radially symmetric animals such as jellyfish...
electrical activity, cold diuresis, and non-cardiogenic pulmonary edema.
Diagnosis
Accurate determination of core temperature often requires a special low temperature thermometer, as most clinical thermometers do not measure accurately below 34.4°C (94°F). A low temperature thermometer can be placed rectally, esophageally, or in the bladder. The classical ECG finding of hypothermia is the Osborn J waveOsborn wave
Osborn waves are a electrocardiogram finding....
. Also, ventricular fibrillation
Ventricular fibrillation
Ventricular fibrillation is a condition in which there is uncoordinated contraction of the cardiac muscle of the ventricles in the heart, making them quiver rather than contract properly. Ventricular fibrillation is a medical emergency and most commonly identified arrythmia in cardiac arrest...
frequently occurs at <28°C (82.4°F) and asystole
Asystole
In medicine, asystole is a state of no cardiac electrical activity, hence no contractions of the myocardium and no cardiac output or blood flow...
at <20°C (68°F). The Osborn J may look very similar to those of an acute ST elevation myocardial infarction. Thrombolysis as a reaction to the presence of Osborn J waves is not indicated, as it would only worsen the underlying coagulopathy
Coagulopathy
Coagulopathy is a condition in which the blood’s ability to clot is impaired. This condition can cause prolonged or excessive bleeding, which may occur spontaneously or following an injury or medical and dental procedures.The normal clotting process depends on the interplay of various proteins in...
caused by hypothermia.
As a hypothermic person's heart rate may be very slow, prolonged palpation could be required before detecting a pulse. In 2005 American Heart Association
American Heart Association
The American Heart Association is a non-profit organization in the United States that fosters appropriate cardiac care in an effort to reduce disability and deaths caused by cardiovascular disease and stroke. It is headquartered in Dallas, Texas...
recommended at least 30 – 45 seconds to verify the absence of a pulse before initiating CPR.
Most physicians are recommended not to declare a patient dead until their body is warmed to a normal body temperature, since extreme hypothermia can suppress heart and brain function.
Prevention
Appropriate clothing helps to prevent hypothermia. SyntheticSynthetic fabric
Synthetic fabrics are textiles made from synthetic fibers. They are used primarily to make clothing. A synthetic fabric is plastic fabric. It is also used to cover skin of androids so it looks human like. Some of the examples of synthetic clothings were usually made of polyester, acrylic, and nylon....
and wool
Wool
Wool is the textile fiber obtained from sheep and certain other animals, including cashmere from goats, mohair from goats, qiviut from muskoxen, vicuña, alpaca, camel from animals in the camel family, and angora from rabbits....
fabrics are superior to cotton as they provide better insulation when wet and dry. Some synthetic fabrics, such as polypropylene and polyester, are used in clothing designed to wick perspiration away from the body, such as liner socks and moisture-wicking undergarments.
The United States Coast Guard
United States Coast Guard
The United States Coast Guard is a branch of the United States Armed Forces and one of the seven U.S. uniformed services. The Coast Guard is a maritime, military, multi-mission service unique among the military branches for having a maritime law enforcement mission and a federal regulatory agency...
promotes using life vests as a method of protection against hypothermia through the 50/50/50 rule: If someone is in 50 °F (10 °C) water for 50 minutes, he/she has a 50 percent better chance of survival if wearing a life jacket. A heat escape lessening position
Heat escape lessening position
The heat escape lessening position , is a way to position oneself to reduce heat loss in cold water. It is taught as part of the curriculum in Australia, North America and Ireland for lifeguard and boating safety training...
can be used to increase survival in cold water.
Management
| Degree | Rewarming technique |
|---|---|
| Mild | Passive rewarming |
| Moderate | Active external rewarming |
| Severe | Active internal rewarming |
Aggressiveness of treatment is matched to the degree of hypothermia. Treatment ranges from noninvasive, passive external warming, to active external rewarming, to active core rewarming. In severe cases resuscitation begins with simultaneous removal from the cold environment and concurrent management of the airway, breathing, and circulation. Rapid rewarming is then commenced. A minimum of patient movement is recommended as aggressive handling may increase risks of a dysrhythmia
Cardiac dysrhythmia
Cardiac dysrhythmia is any of a large and heterogeneous group of conditions in which there is abnormal electrical activity in the heart. The heart beat may be too fast or too slow, and may be regular or irregular.Some arrhythmias are life-threatening medical emergencies that can result in cardiac...
.
Hypoglycemia
Hypoglycemia
Hypoglycemia or hypoglycæmia is the medical term for a state produced by a lower than normal level of blood glucose. The term literally means "under-sweet blood"...
is a frequent complication of hypothermia, and therefore needs to be tested for and treated. Intravenous thiamine
Thiamine
Thiamine or thiamin or vitamin B1 , named as the "thio-vitamine" is a water-soluble vitamin of the B complex. First named aneurin for the detrimental neurological effects if not present in the diet, it was eventually assigned the generic descriptor name vitamin B1. Its phosphate derivatives are...
and glucose
Glucose
Glucose is a simple sugar and an important carbohydrate in biology. Cells use it as the primary source of energy and a metabolic intermediate...
is often recommended as many causes of hypothermia are complicated by Wernicke's encephalopathy
Wernicke's encephalopathy
Wernicke encephalopathy is a syndrome characterised by ataxia, ophthalmoplegia, confusion, and impairment of short-term memory.It is caused by lesions in the medial thalamic nuclei, mammillary bodies, periaqueductal and periventricular brainstem nuclei, and superior cerebellar vermis, often...
.
Rewarming
Rewarming can be achieved using a number of different methods including passive external rewarming, active external rewarming, and active internal rewarming. Passive external rewarming involves the use of a person's own heat generating ability through the provision of properly insulated dry clothing and moving to a warm environment. It is recommended for those with mild hypothermia. Active external rewarming involves applying warming devices externally such as warmed forced air (a Bair Hugger is a commonly used device). In austere environments hypothermia can sometimes be treated by placing a hot water bottleHot water bottle
A hot water bottle is a container filled with hot water and sealed with a stopper, used to provide warmth, typically whilst in bed, but also for the application of heat to a specific part of the body....
in both armpits and groin. It is recommended for moderate hypothermia. Active core rewarming involves the use of intravenous warmed fluids, irrigation of body cavities with warmed fluids (the thorax, peritoneal, stomach, or bladder), use of warm humidified inhaled air, or use of extracorporeal
Extracorporeal
An extracorporeal medical procedure is a medical procedure which is performed outside the body.-Circulatory procedures:A procedure in which blood is taken from a patient's circulation to have a process applied to it before it is returned to the circulation...
rewarming such as via a heart lung machine. Extracorporeal rewarming is the fastest method for those with severe hypothermia.
Intravenous fluids
As most people are moderately dehydrated due to hypothermia induced cold diuresis, intravenous fluids are often helpful ( 250–500 cc 5% dextrose and normal saline warmed to a temperature of 40–45 C is often recommended ).Rewarming collapse
Rewarming collapse (or rewarming shock) is a sudden drop in blood pressureBlood pressure
Blood pressure is the pressure exerted by circulating blood upon the walls of blood vessels, and is one of the principal vital signs. When used without further specification, "blood pressure" usually refers to the arterial pressure of the systemic circulation. During each heartbeat, BP varies...
in combination with a low cardiac output
Cardiac output
Cardiac output is the volume of blood being pumped by the heart, in particular by a left or right ventricle in the time interval of one minute. CO may be measured in many ways, for example dm3/min...
which may occur during active treatment of a severely hypothermic person. There is theoretical concern that external rewarming rather than internal rewarming may increase the risk. However, recent studies have not supported these concerns.
Prognosis
There is considerable evidence that children who suffer near-drowningDrowning
Drowning is death from asphyxia due to suffocation caused by water entering the lungs and preventing the absorption of oxygen leading to cerebral hypoxia....
accidents in water near 0°C (32°F) can be revived over an hour after losing consciousness. The cold water lowers metabolism
Metabolism
Metabolism is the set of chemical reactions that happen in the cells of living organisms to sustain life. These processes allow organisms to grow and reproduce, maintain their structures, and respond to their environments. Metabolism is usually divided into two categories...
, allowing the brain to withstand a much longer period of hypoxia
Hypoxia (medical)
Hypoxia, or hypoxiation, is a pathological condition in which the body as a whole or a region of the body is deprived of adequate oxygen supply. Variations in arterial oxygen concentrations can be part of the normal physiology, for example, during strenuous physical exercise...
. While survival is possible, mortality
Mortality rate
Mortality rate is a measure of the number of deaths in a population, scaled to the size of that population, per unit time...
from severe or profound hypothermia remains high despite optimal treatment. Studies estimate mortality at between 38% – 75%. If there are obvious fatal injuries or the chest is too frozen, compression resuscitation is futile.
Epidemiology
In the past hypothermia occurred most frequently in homeless people, but recreational exposure to cold environments is now the main cause of hypothermia. Between 1995 and 2004 in the United States an average of 1560 cold-related emergency department visits occurred per year and in the years 1999 to 2004 an average of 647 people died per year due to hypothermia.History
Russia
Russia or , officially known as both Russia and the Russian Federation , is a country in northern Eurasia. It is a federal semi-presidential republic, comprising 83 federal subjects...
in 1812. Loss of life to hypothermia continued through the first and second world wars, especially in the Battle of Stalingrad. Civilian examples of deaths caused by hypothermia are found during the sinkings of the RMS Titanic and RMS Lusitania
RMS Lusitania
RMS Lusitania was a British ocean liner designed by Leonard Peskett and built by John Brown and Company of Clydebank, Scotland. The ship entered passenger service with the Cunard Line on 26 August 1907 and continued on the line's heavily-traveled passenger service between Liverpool, England and New...
.
In other animals
Many animals other than humans often induce hypothermia during hibernationHibernation
Hibernation is a state of inactivity and metabolic depression in animals, characterized by lower body temperature, slower breathing, and lower metabolic rate. Hibernating animals conserve food, especially during winter when food supplies are limited, tapping energy reserves, body fat, at a slow rate...
or torpor
Torpor
Torpor, sometimes called temporary hibernation is a state of decreased physiological activity in an animal, usually characterized by a reduced body temperature and rate of metabolism. Animals that go through torpor include birds and some mammals such as mice and bats...
.
Water bears (Tardigrade
Tardigrade
Tardigrades form the phylum Tardigrada, part of the superphylum Ecdysozoa. They are microscopic, water-dwelling, segmented animals with eight legs. Tardigrades were first described by Johann August Ephraim Goeze in 1773...
), microscopic multicellular organisms, can survive freezing
Freezing
Freezing or solidification is a phase change in which a liquid turns into a solid when its temperature is lowered below its freezing point. The reverse process is melting....
at low temperatures by replacing most of their internal water with the sugar
Sugar
Sugar is a class of edible crystalline carbohydrates, mainly sucrose, lactose, and fructose, characterized by a sweet flavor.Sucrose in its refined form primarily comes from sugar cane and sugar beet...
trehalose
Trehalose
Trehalose, also known as mycose or tremalose, is a natural alpha-linked disaccharide formed by an α,α-1,1-glucoside bond between two α-glucose units. In 1832, H.A.L. Wiggers discovered trehalose in an ergot of rye, and in 1859 Marcellin Berthelot isolated it from trehala manna, a substance made...
, preventing it from crystallization that otherwise damage cell membranes.