Hypothermia
Classification and external resources
During Napoleon Bonaparte's retreat from Russia in the winter of 1812 many troops suffered from hypothermia.
ICD-10	T68
ICD-9	991.6
DiseasesDB	6542
eMedicine	med/1144
MeSH	D007035

Hypothermia (from Greek υποθερμία) 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.

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 13.0 °C (55.4 °F), in a near-drowning incident involving a 7-year-old girl in Sweden in December 2010.^[1]

Classification[link]

Normal human body temperature in adults is 34.4–37.8 °C (94–100 °F).^[8] Sometimes a narrower range is stated, such as 36.5–37.5 °C (98–100 °F).^[9] 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).^[10] 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).^[5]

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.^[11]
• Frostbite involves the freezing and destruction of tissue.^[11]
• Frostnip is a superficial cooling of tissues without cellular destruction.^[12]
• Trench foot or immersion foot is due to repetitive exposure to wet, non-freezing temperatures.^[11]

Signs and symptoms[link]

The signs and symptoms vary depending on the degree of hypothermia and may be divided by the three stages of severity.

Mild[link]

Symptoms of mild hypothermia may be vague^[13] with sympathetic nervous system excitation (shivering, hypertension, tachycardia, tachypnea, and vasoconstriction). These are all physiological responses to preserve heat.^[14] Cold diuresis, mental confusion, as well as hepatic dysfunction may also be present.^[15] Hyperglycemia may be present, as glucose consumption by cells and insulin secretion both decrease, and tissue sensitivity to insulin may be blunted.^[16] Sympathetic activation also releases glucose from the liver. In many cases, however, especially in alcoholic patients, hypoglycemia appears to be a more common presentation.^[16] Hypoglycemia is also found in many hypothermic patients because hypothermia often is a result of hypoglycemia.^[17]

Moderate[link]

Low body temperature results in shivering becoming more violent. Muscle mis-coordination becomes apparent.^[18][19][20] 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[link]

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).^[15]

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.^{[citation needed]}

Paradoxical undressing[link]

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.^[21][22]

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.^[23]

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.^[23]

Terminal burrowing[link]

An apparent self-protective behaviour known as terminal burrowing, or hide-and-die syndrome^[24], occurs in the final stages of hypothermia. The afflicted will enter small, enclosed spaces, such as underneath beds or behind wardrobes. It is often associated with paradoxical undressing.^[25]

Causes[link]

The rate of hypothermia is strongly related to age in the United States.

Hypothermia usually occurs from exposure to low temperatures, and is frequently complicated by alcohol. Any condition that decreases heat production, increases heat loss, or impairs thermoregulation, however, may contribute.^[26] 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.^[27][28] Hypothermia also occurs frequently in major trauma. Hypothermia also is observed in severe cases of anorexia nervosa.

Alcohol[link]

Alcohol 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.^[29] Between 33 and 73% of cases of hypothermia are complicated by alcohol.^[30][31]

Water[link]

Hypothermia continues to be a major limitation to diving in cold water.^[18] The limitation of finger dexterity due to pain or numbness decreases general safety and work capacity, which consequently increases the risk of other injuries.^[18][20] 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.^[18]

Heat is lost more quickly in water^[18] 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.^[32] A notable example of this occurred during the sinking of the Titanic, in which most people who entered the −2 °C (28 °F) water died within 15–30 minutes.^[33]

Water at a temperature of 26 °C (79 °F) will, after prolonged exposure, lead to hypothermia.^[34]

Pathophysiology[link]

Heat is primarily generated in muscle tissue, including the heart, and in the liver, while it is lost through the skin (90%) and lungs (10%).^[13] Heat production may be increased 2 to 4 fold through muscle contractions ( i.e. exercise and shivering ).^[13] Rates of bodily heat loss are determined, as with any object, by convection, conduction, and radiation.^[13] 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.^[35]

Diagnosis[link]

Atrial fibrillation and Osborn J waves in a person with hypothermia. Note what could be mistaken for ST elevation.

Accurate determination of core temperature often requires a special low temperature thermometer, as most clinical thermometers do not measure accurately below 34.4 °C (93.9 °F).^[14] A low temperature thermometer can be placed rectally, esophageally, or in the bladder. The classical ECG finding of hypothermia is the Osborn J wave. Also, ventricular fibrillation frequently occurs at <28 °C (82 °F) and asystole at <20 °C (68 °F).^[13] The Osborn J may look very similar to those of an acute ST elevation myocardial infarction.^[15] 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.^[36]

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.^[37]

Prevention[link]

Appropriate clothing helps to prevent hypothermia. Synthetic 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.^{[citation needed][38]} A heat escape lessening position can be used to increase survival in cold water.

Management[link]

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.^[14] 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.^[36]

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.^[39]

Rewarming[link]

Rewarming can be achieved using a number of different methods including passive external rewarming, active external rewarming, and active internal rewarming.^[40] 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.^[41] It is recommended for those with mild hypothermia.^[41] Active external rewarming involves applying warming devices externally such as warmed forced air (a Bair Hugger is a commonly used device).^[41] In austere environments hypothermia can sometimes be treated by placing a hot water bottle in both armpits and groin.^[42] It is recommended for moderate hypothermia.^[41] 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.^[40] Extracorporeal rewarming is the fastest method for those with severe hypothermia.^[41]

Intravenous fluids[link]

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).^[14]

Rewarming collapse[link]

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.^[43][44] There is theoretical concern that external rewarming rather than internal rewarming may increase the risk. However, recent studies have not supported these concerns.^[36]

Prognosis[link]

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.^[45] 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%^[46][47] and 75%.^[13] If there are obvious fatal injuries or the chest is too frozen, compression resuscitation is futile.^[36]

Epidemiology[link]

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.^[27][48]

History[link]

The armies of Napoleon retreat from Russia in 1812.

Snow-storm: Hannibal and His Army Crossing the Alps, J. M. W. Turner

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 the Second Punic War (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.^[49]

Civilian examples of deaths caused by hypothermia are found during the sinkings of the RMS Titanic and RMS Lusitania, and more recently of the MS Estonia.^[50][51][52]

In other animals[link]

Many animals other than humans often induce hypothermia during hibernation 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.

See also[link]

Underwater diving portal

References[link]

Bibliography

External links[link]

Find more about Hypothermia on Wikipedia's sister projects:
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	Textbooks from Wikibooks

• Princeton Outdoor Guide to Hypothermia
• Wilderness Management of Hypothermia

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'Chris Ryan'
Born	1961 (age 50–51) Rowlands Gill, England
Allegiance	United Kingdom
Service/branch	British Army
Years of service	1978–1994
Rank	Sergeant
Unit	Special Air Service
Battles/wars	Gulf War
Awards	Military Medal
Other work	Author, Security Consultant.

Sergeant ‘Chris Ryan’ MM (born 1961, Rowlands Gill, Tyne and Wear) is the pseudonym of a former British Special Forces operative and soldier turned novelist.^[1] Ryan came to public prominence for being the only member of the eight-man SAS mission Bravo Two Zero to escape, during the First Gulf War, 1991.

He has subsequently written several books, including The One That Got Away and "One Good Turn", a specially commissioned story for the Quick Reads Initiative, aimed at improving adult literacy. 'The One that Got Away' has since been heavily criticised by Trooper Mike Coburn and Sergeant Andy McNab, two of the surviving members of the patrol, particularly in regard to its negative portrayal of Sergeant Vince Phillips, who died of hypothermia during the patrol's attempted escape.^{[citation needed]}

Background[link]

Ryan was born in Rowlands Gill, Tyne and Wear, North East England. After attending Hookergate secondary school, he enrolled in the Army as a boy soldier at 16. His cousin was in the 23rd SAS Reserves and invited Ryan to come up and "see what it's like to be in the army".^[2] Ryan did this nearly every weekend, almost passing selection several times, but he was too young to continue and do 'test week'. When he was old enough, he passed selection into the 23rd SAS. Shortly after that he began selection for the Regular 22 Regiment and joined 'B' squadron as a medic. Needing a parent regiment, Ryan and a soldier who had joined the SAS from the Royal Navy, spent eight weeks with the Parachute Regiment before returning to 'B' Squadron.^[3] He spent the next seven years carrying out both covert and overt operations with the SAS around the world.

Ryan's assignment included training Khmer Rouge troops in 1981 to attack Vietnamese forces that had pushed them out of Cambodia. Journalist John Pilger wrote in October 2009, "Incredibly, the Thatcher government had continued to support the defunct Pol Pot regime in the United Nations and even sent the SAS to train his exiled troops in camps in Thailand and Malaysia."^[4] In March 2009 Ryan admitted: "John Pilger, the foreign correspondent, discovered we were training the Khmer Rouge in the Far East. We were sent home and I had to return the £10,000 we'd been given to pay for food and accommodation."^[5]

Bravo Two Zero[link]

Ryan was a team member of the ill-fated Bravo Two Zero patrol in Iraq during the First Gulf War. The patrol was sent to "gather intelligence,... find a good LUP (lying up position) and set up an OP"^[6] on the main supply route (MSR) between Baghdad and North-Western Iraq, and eventually take out the Scud Missile Launchers. However, they were compromised and forced to head towards Syria on foot.

Ryan made SAS history with the "longest escape and evasion by an SAS trooper or any other soldier", covering 100 miles (160 km) more than SAS trooper Jack Sillito had in the Sahara Desert in 1942. Ryan completed a 300 kilometres (190 mi) tab from an observation point on the Iraq Main Supply Route (MSR) between Baghdad and North-Western Iraq to the Syrian Border.^[7]

During his escape, Ryan suffered injuries from drinking water contaminated with nuclear waste. Besides suffering severe muscle atrophy, he lost a potentially fatal 16 kg (35 lb) and did not return to operational duties. Instead, he selected and trained potential recruits, finally being honourably discharged from the SAS in 1994.

Zaire[link]

Ryan was also a member of an SAS team sent to protect the British Embassy in Zaire. The SAS were to ensure that all British diplomatic staff were safely evacuated from the country before the First Congo War. The operation was meant to last only three days, but eventually took one month.^[8]

Post-SAS work[link]

Since leaving the SAS, Ryan has written several books. The One That Got Away, his non-fiction account of the Bravo Two Zero mission, is well known, as are fictional best-sellers like Strike Back (2007), which was adapted into the TV show, and Firefight (September 2008). He also writes fictional books for teenage readers, including the Alpha Force Series and "Code Red". Ryan combines successfully writing his best-selling books with giving security lectures and presenting television documentaries such as Hunting Chris Ryan.

In 2005, Ryan presented a Sky One show called How Not to Die, detailing how not to die in various life-threatening situations, including violent burglary, mugging, and violent attacks. He acted as the military advisor on the video game I.G.I.-2: Covert Strike, helping to make the game more accurate to real-life military operations, tactics, weapons and equipment. Ryan both co-created, and starred in the TV show Ultimate Force, was a military, technical advisor and played the role of Blue Troop leader Johnny Bell in series 1. He trained and managed a six-man team to represent Team GB at Sure for Men's Extreme Pamplona Chase in Spain, and starred in Hunting Chris Ryan with the BBC which later aired on the Military Channel as 'Special Forces Manhunt'. Ryan produced several programmes titled Terror Alert: Could You Survive, in each programme he demonstrated how to survive disasters including, flooding, nuclear terrorist attack, mass blackouts, and plane hi-jacking.

He was featured in the Derren Brown Series, Mind Control episode 3 in which Ryan had to booby-trap a course for Derren to follow whilst blind folded.

He lectures in business motivation, and is currently a bodyguard in the USA. In 2009 Ryan starred in "Elite World Cops" aired on Bravo. In the show, Ryan spends time with various law enforcement agencies around the world, giving him an insight to the war on terrorism and drug trade but from a law enforcement perspective.^[9]

Ryan has a new program currently showing on Bravo called Armed and Dangerous.

He has written a romantic novel, The Fisherman's Daughter, under the pseudonym Molly Jackson.^[10]

Books[link]

Ryan has written the following books:^[11]

Non-Fiction[link]

• The One That Got Away (1995)
• Chris Ryan's SAS Fitness Book (1999)
• Chris Ryan's Ultimate Survival Guide (2003)
• Chris Ryan fight to win (2009)

Fiction[link]

Geordie Sharp (character)

• Stand By, Stand By (1996)
• Zero Option (1997)
• The Kremlin Device (1998)
• Tenth Man Down (1999)

Matt Browning (character)

• Greed (2003)
• The Increment (2004)

Other

• The Hit List (2000)
• The Watchman (2001)
• Land Of Fire (2002)
• Blackout (2005)
• Ultimate Weapon (2006)
• Strike Back (2007)
• Firefight (2008)
• Who Dares Wins (2009)
• The Kill Zone' (2010)
• Agent 21 (2011)
• Medal of Honor (2011)
• Killing for the Company (2011)

Code Red

• Flash Flood (2006)
• Wildfire (2007)
• Outbreak (2007)
• Vortex (2008)
• Twister (2008)
• Battleground (2009)

Alpha Force

• Alpha Force 1: Survival (2002)
• Alpha Force 2: Rat-catcher (2002)
• Alpha Force 3: Desert Pursuit (2003)
• Alpha Force 4: Hostage (2003)
• Alpha Force 5: Red Centre (2004)
• Alpha Force 6: Hunted (2004)
• Alpha Force 7: Blood Money (2005)
• Alpha Force 8: Fault Line (2005)
• Alpha Force 9: Black Gold (2005)
• Alpha Force 10: Untouchable (2005)

Quick Reads

• One Good Turn (2008)

Agent 21

• Agent 21 (2011)
• Agent 21: Reloaded (2012)

References[link]

External links[link]

• Official Facebook page
• Official Website
• Chris Ryan at the Internet Movie Database
• Chris Ryan's Elite Police DVD release
• List of books
• Chris Ryan audio interview, November 2008 with Scottish Book Trust
• Chris Ryan's Strike Back on Sky 1
• Chris Ryan's Strike Back Video Trailer