Hypothermia

Definition:-
Hypothermia  is a condition in which core temperature drops below the required temperature for normal metabolism and body functions which is defined as 35.0 °C (95.0 °F). Body temperature is usually maintained near a constant level of 36.5–37.5 °C (98–100 °F) 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.

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When your body temperature drops, your heart, nervous system and other organs cannot work correctly. Left untreated, hypothermia eventually leads to complete failure of your heart and respiratory system and to death.

Hypothermia is most often caused by exposure to cold weather or immersion in a cold body of water. Primary treatments are methods to warm the body back to a normal temperature.

Hypothermia is the opposite of hyperthermia which is present in heat exhaustion and heat stroke. The lowest documented body temperature from which anyone has recovered was 13.0 °C (55.4 °F), in a drowning incident involving a 7-year-old girl in Sweden in December 2010

Clasification:
Normal human body temperature in adults is 34.4–37.8 °C (94–100 °F). Sometimes a narrower range is stated, such as 36.5–37.5 °C (98–100 °F). Hypothermia is defined as any body temperature below 35.0 °C (95.0 °F). It is subdivided into four different degrees, mild 32–35 °C (90–95 °F); moderate, 28–32 °C (82–90 °F); severe, 20–28 °C (68–82 °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:

*Chilblains are superficial ulcers of the skin that occur when a predisposed individual is repeatedly exposed to cold.
*Frostbite involves the freezing and destruction of tissue.
*Frostnip is a superficial cooling of tissues without cellular destruction.
*Trench foot or immersion foot is due to repetitive exposure to wet, non-freezing temperatures

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 (shivering, 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.

Moderate:
Low body temperature results in shivering becoming more violent.(Shivering is your body’s automatic defense against cold temperature — an attempt to warm itself. Constant shivering is a key sign of hypothermia) 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:
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 victim exhibits incoherent/irrational behavior including terminal burrowing or even a stupor. Pulse and respiration rates decrease significantly, but fast heart rates (ventricular tachycardia, atrial fibrillation) can occur. Major organs fail. Clinical death occurs. Because of decreased cellular activity in stage 3 hypothermia, the body will actually take longer to undergo brain death.

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 °F).

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, 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:
In the final stages of hypothermia, the brain stem produces a burrowing-like behavior. Similar to hibernation behavior in animals, individuals with severe hypothermia are often found in small, enclosed spaces, such as under the bed or behind wardrobes.

Cause:
Hypothermia occurs when your body loses heat faster than it produces it. The most common causes of hypothermia are exposure to cold weather conditions or cold water, but prolonged exposure to any environment colder than your body can lead to hypothermia if you aren’t dressed appropriately or can’t control the conditions. Specific conditions leading to hypothermia include:

*Wearing clothes that aren’t warm enough for weather conditions

*Staying out in the cold too long

*Unable to get out of wet clothes or move to a warm, dry location

*Accidental falls in water, as in a boating accident

*Inadequate heating in the home, especially for older people and infants

*Air conditioning that is too cold, especially for older people and infants

How your body loses heat
The mechanisms of heat loss from your body include the following:

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*Radiated heat. Most heat loss is due to heat radiated from unprotected surfaces of your body. Your head has a large surface area and accounts for about half of all heat loss.

*Direct contact. If you’re in direct contact with something very cold, such as cold water or the cold ground, heat is conducted away from your body. Because water is very good at transferring heat from your body, body heat is lost much faster in cold water than in cold air. Water that is 65 F (18 C) — a relatively mild air temperature — can lead to hypothermia very quickly. Similarly, heat loss from your body is much faster if your clothes are wet, as when you’re caught out in the rain.Wind.

*Wind removes body heat by carrying away the thin layer of warm air at the surface of your skin. A wind chill factor is important in causing heat loss. For example, if the outside temperature is 32 F (0 C) and the wind chill factor is minus 15 F (minus 26 C), your body loses heat as quickly as if the actual temperature outside were minus 15 F (minus 26 C).

Risk Factors:
A number of factors can increase the risk of developing hypothermia:

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*Older age. People age 65 and older are more vulnerable to hypothermia for a number of reasons. The body’s ability to regulate temperature and to sense cold may lessen with age. Older people are also more likely to have a medical condition that affects temperature regulation. Some older adults may not be able to communicate when they are cold or may not be mobile enough to get to a warm location.

*Very young age. Children lose heat faster than adults do. Children have a larger head-to-body ratio than adults do, making them more prone to heat loss through the head. Children may also ignore the cold because they’re having too much fun to think about it. And they may not have the judgment to dress properly in cold weather or to get out of the cold when they should. Infants may have a special problem with the cold because they have less efficient mechanisms for generating heat.

*Mental impairment. People with a mental illness, dementia or another condition that impairs judgment may not dress appropriately for the weather or understand the risk of cold weather. People with dementia may wander from home or get lost easily, making them more likely to be stranded outside in cold or wet weather.Alcohol and drug use.

*Alcohol may make your body feel warm inside, but it causes your blood vessels to dilate, or expand, resulting in more rapid heat loss from the surface of your skin. The use of alcohol or recreational drugs can impair your judgment about the need to get inside or wear warm clothes in cold weather conditions. If a person is intoxicated and passes out in cold weather, he or she is likely to develop hypothermia.

*Certain medical conditions. Some health disorders affect your body’s ability to regulate body temperature. Examples include underactive thyroid (hypothyroidism), malnutrition, stroke, severe arthritis, Parkinson’s disease, trauma, spinal cord injuries, burns, disorders that affect sensation in your extremities (for example, nerve damage in the feet of people with diabetes), dehydration and any condition that limits activity or restrains the normal flow of blood.

*Medications. A number of antipsychotic drugs and sedatives can impair the body’s ability to regulate its temperature.

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 Osborne J wave. 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.

Treatment:-
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

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 bottle 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.

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 pressure 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.

Prognosis:-
There is considerable evidence that children who suffer near-drowning 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 chest is too frozen, compression resuscitation is futile

Prevention:
The Government offers extra support for some of the most vulnerable people in the form of winter fuel payments, to help keep their homes warm.

Other ways to prevent hypothermia include:
•Stay indoors as much as possible and limit your exposure to the cold
•Eat regularly and include plenty of carbohydrates (the body needs a reliable and constant energy supply to generate heat)
•Keep as active as possible
•Avoid alcohol – it causes dilation of peripheral blood vessel, increasing heat loss
•Avoid caffeine – it’s a diuretic and increases the risk of dehydration, which aggravates heat loss
•Avoid nicotine – it constricts blood vessels and increases the risk of cold damage such as frostbite
•Wear multiple thin layers of clothing that help to trap air layers and hence traps heat, rather than one thick jumper
•If you go outside, always wear a hat (it can prevent as much as 20 per cent of heat loss), scarf and gloves
•Take a flask of caffeine-free hot drink with you, and click-activated heat pads you can keep in your pockets to set off when you need them

Disclaimer: This information is not meant to be a substitute for professional medical advise or help. It is always best to consult with a Physician about serious health concerns. This information is in no way intended to diagnose or prescribe remedies.This is purely for educational purpose

Resources:
http://www.bbc.co.uk/health/physical_health/conditions/hypothermia1.shtml
http://www.mayoclinic.com/health/hypothermia/DS00333
http://en.wikipedia.org/wiki/Hypothermia

http://trialx.com/curebyte/2011/05/22/clinical-trials-and-images-of-hypothermia/

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