Editing Hyperthermia

{{Short description|Elevated body temperature due to failed thermoregulation}}
{{About|hyperthermia as a condition|hyperthermia as a treatment|hyperthermia therapy}}
{{Distinguish|hypothermia|fever}}
{{More citations needed|date=October 2023}}
{{use dmy dates|date=August 2015}}
{{Infobox medical condition
 |name          = Hyperthermia
 |synonym       = Overheating
 |image         = Clinical thermometer 38.7.JPG
 |image_size    =
 |alt           =
 |caption       = An analog [[medical thermometer]] showing a temperature of {{convert|38.7|C|F}}
 |pronounce     =
 |specialty     = [[Critical care medicine]]
 |symptoms      = Lack of perspiration, confusion, [[delirium]], decreased blood pressure, increased heart rate and respiration rate, symptoms of [[dehydration]]
 |complications = [[Organ failure]], [[unconsciousness]]
 |onset         =
 |duration      =
 |types         =
 |causes        = [[Heat stroke]]<ref name="heatstroke-newengland">{{Cite journal|last1=Bouchama|first1=Abderrezak|last2=Knochel|first2=James P.|date=2002-06-20|title=Heat Stroke|url=http://dx.doi.org/10.1056/nejmra011089|journal=New England Journal of Medicine|volume=346|issue=25|pages=1978–1988|doi=10.1056/nejmra011089|pmid=12075060|issn=0028-4793}}</ref>
 |risks         = Exposure to hot and/or humid environments, physical exertion, wearing [[personal protective equipment]] that covers the body, [[heatwaves]]
 |diagnosis     = Based on symptoms or [[body temperature]] above {{convert|37.7|C|F}}<ref name=Harrisons/>
 |differential  = [[Fever]]<ref name=NC08/>
 |prevention    = Maintaining a moderate temperature, regular hydration, taking regular breaks
 |treatment     = '''Mild:''' Staying away from hot environments, rehydrating oneself, mechanical cooling, use of a dehumidifier<br />'''Severe:''' [[intravenous]] [[Fluid replacement|hydration]], [[gastric lavage]] with iced [[Saline water|saline]], [[hemodialysis]], [[cold water immersion|immersing in ice water]]
 |medication    =
 |prognosis     =
 |frequency     =
 |deaths        =
}}

<!-- Definition -->
'''Hyperthermia''', also known simply as '''overheating''', is a condition in which an individual's body temperature is elevated beyond normal due to failed [[thermoregulation]]. The person's body produces or absorbs more [[heat]] than it dissipates. When extreme temperature elevation occurs, it becomes a [[medical emergency]] requiring immediate treatment to prevent disability or death.{{Citation needed|date=February 2022}} Almost half a million deaths are recorded every year from hyperthermia.{{Citation needed|date=February 2022}}

<!-- Cause -->
The most common causes include [[heat stroke]] and adverse reactions to drugs. Heat stroke is an [[body temperature|acute temperature elevation]] caused by exposure to excessive heat, or combination of heat and humidity, that overwhelms the heat-regulating mechanisms of the body. The latter is a relatively rare side effect of many drugs, particularly those that affect the [[central nervous system]]. [[Malignant hyperthermia]] is a rare complication of some types of [[general anesthesia]]. Hyperthermia can also be caused by a [[traumatic brain injury]].<ref>{{Cite journal|last1=Thompson|first1=Hilaire J.|last2=Tkacs|first2=Nancy C.|last3=Saatman|first3=Kathryn E.|last4=Raghupathi|first4=Ramesh|last5=McIntosh|first5=Tracy K.|date=April 2003|title=Hyperthermia following traumatic brain injury: a critical evaluation|url=https://pubmed.ncbi.nlm.nih.gov/12742737/|journal=Neurobiology of Disease|volume=12|issue=3|pages=163–173|doi=10.1016/s0969-9961(02)00030-x|issn=0969-9961|pmid=12742737|s2cid=23680754}}</ref><ref>{{Cite journal|last1=Truettner|first1=Jessie S.|last2=Bramlett|first2=Helen M.|last3=Dietrich|first3=W. Dalton|date=2018-04-01|title=Hyperthermia and Mild Traumatic Brain Injury: Effects on Inflammation and the Cerebral Vasculature|journal=Journal of Neurotrauma|volume=35|issue=7|pages=940–952|doi=10.1089/neu.2017.5303|issn=0897-7151|pmc=5865622|pmid=29108477}}</ref><ref>{{Cite journal|last1=Thompson|first1=H. J.|last2=Pinto-Martin|first2=J.|last3=Bullock|first3=M. R.|date=2003-05-01|title=Neurogenic fever after traumatic brain injury: an epidemiological study|journal=Journal of Neurology, Neurosurgery & Psychiatry|language=en|volume=74|issue=5|pages=614–619|doi=10.1136/jnnp.74.5.614|issn=0022-3050|pmid=12700304|pmc=1738450|doi-access=free}}</ref>

Hyperthermia differs from [[fever]] in that the body's [[Thermoregulation#Normal human temperature|temperature set point]] remains unchanged. The opposite is [[hypothermia]], which occurs when the temperature drops below that required to maintain normal metabolism. The term is from [[Greek language|Greek]]  ὑπέρ, ''hyper'', meaning "above", and θέρμος, ''thermos'', meaning "heat".

==Classification==
{{HumanTemperature}}
In humans, hyperthermia is defined as a temperature greater than {{convert|37.5|–|38.3|C|F}}, depending on the reference used, that occurs without a change in the body's  [[Thermoregulation#Normal human temperature|temperature set point]].<ref name=NC08/><ref name=CC09/>

The [[normal human body temperature]] can be as high as {{convert|37.7|C|F}} in the late afternoon.<ref name=Harrisons/>  Hyperthermia requires an elevation from the temperature that would otherwise be expected. Such elevations range from mild to extreme; body temperatures above {{convert|40|C|F}} can be life-threatening.

==Signs and symptoms==
An early stage of hyperthermia can be "heat exhaustion" (or "heat prostration" or "heat stress"), whose symptoms can include heavy sweating, rapid breathing and a fast, weak pulse. If the condition progresses to heat stroke, then hot, dry skin is typical<ref name=Harrisons/> as [[blood vessel]]s dilate in an attempt to increase heat loss. An inability to cool the body through [[perspiration]] may cause [[dry skin]]. Hyperthermia from neurological disease may include [[anhidrosis|little or no sweating]], cardiovascular problems, and confusion or [[delirium]].

Other signs and symptoms vary. Accompanying dehydration can produce [[nausea]], vomiting, [[headaches]], and [[low blood pressure]] and the latter can lead to [[fainting]] or [[dizziness]], especially if the standing position is assumed quickly.

In severe heat stroke, confusion and aggressive behavior may be observed. Heart rate and respiration rate will increase ([[tachycardia]] and [[tachypnea]]) as blood pressure drops and the heart attempts to maintain adequate [[Circulatory system|circulation]]. The decrease in blood pressure can then cause blood vessels to contract reflexively, resulting in a pale or bluish skin color in advanced cases. Young children, in particular, may have [[seizures]]. Eventually, [[organ failure]], [[unconsciousness]] and death will result.

==Causes==
[[Heat stroke]] occurs when thermoregulation is overwhelmed by a combination of excessive metabolic production of heat (exertion), excessive environmental heat, and insufficient or impaired heat loss, resulting in an abnormally high body temperature.<ref name=Harrisons /> In severe cases, temperatures can exceed {{convert|40|C|F}}.<ref name=EMS>{{cite book |title=Emergency Medicine: A Comprehensive Study Guide, Sixth edition |last=Tintinalli |first=Judith  |year=2004 |publisher=McGraw-Hill Professional |isbn=0-07-138875-3 |page=1187}}</ref> Heat stroke may be ''non-exertional'' (classic) or ''exertional''.

===Exertional===
Significant physical exertion in hot conditions can generate heat beyond the ability to cool, because, in addition to the heat, humidity of the environment may reduce the efficiency of the body's normal cooling mechanisms.<ref name=Harrisons>{{cite book|author-link=Anthony Fauci |last=Fauci |first=Anthony |title= Harrison's Principles of Internal Medicine |edition=17th |publisher=McGraw-Hill Professional |year=2008 |isbn=978-0-07-146633-2 |pages=[https://archive.org/details/harrisonsprincip00asfa/page/n155 117]–121 |display-authors=etal |title-link=Harrison's Principles of Internal Medicine}}</ref> Human heat-loss mechanisms are limited primarily to sweating (which dissipates heat by [[evaporation]], assuming sufficiently low [[humidity]]) and [[vasodilation]] of skin vessels (which dissipates heat by [[convection]] proportional to the [[temperature]] difference between the body and its surroundings, according to [[Newton's law of cooling]]). Other factors, such as insufficient water intake, consuming alcohol, or lack of [[air conditioning]], can worsen the problem.

The increase in body temperature that results from a breakdown in thermoregulation affects the body biochemically. [[Enzyme]]s involved in metabolic pathways within the body such as cellular respiration fail to work effectively at higher temperatures, and further increases can lead them to [[Denaturation (biochemistry)|denature]], reducing their ability to catalyse essential chemical reactions. This loss of enzymatic control affects the functioning of major organs with high energy demands such as the heart and brain.<ref>{{Cite web|date=2020-09-22|title=Medically Sound: Crossing Thermometric Barriers (Searing Heat and Freezing Cold)|url=https://urmedlife.blogspot.com/2020/09/crossing-thermometric-borders-searing.html|access-date=2020-11-07|website=Medically Sound}}</ref> Loss of fluid and electrolytes cause [[heat cramps]] – slow muscular contraction and severe muscular spasm lasting between one and three minutes. Almost all cases of heat cramps involve vigorous physical exertion. Body temperature may remain normal or a little higher than normal and cramps are concentrated in heavily used muscles.

===Situational===
[[File:heat-related deaths.jpg|upright=1.6|thumb|alt=Chart showing number of heat-related deaths by date of occurrence and race of decedent versus heat index, Chicago, July 11–27, 1995]]
Situational heat stroke occurs in the absence of exertion. It mostly affects the young and elderly. In the elderly in particular, it can be precipitated by medications that reduce vasodilation and sweating, such as [[anticholinergic]] drugs, antihistamines, and diuretics.<ref name=Harrisons /> In this situation, the body's tolerance for high environmental temperature may be insufficient, even at rest.

Heat waves are often followed by a rise in the death rate, and these 'classical hyperthermia' deaths typically involve the elderly and infirm. This is partly because thermoregulation involves cardiovascular, respiratory and renal systems which may be inadequate for the additional stress because of the existing burden of aging and disease, further compromised by medications. During the July 1995 heatwave in Chicago, there were at least 700 heat-related deaths. The strongest risk factors were being confined to bed, and living alone, while the risk was reduced for those with working air conditioners and those with access to transportation. Even then, reported deaths may be underestimated as diagnosis can be mis-classified as stroke or heart attack.<ref>{{cite journal|title=Heat-related deaths during the July 1995 heat wave in Chicago |vauthors=Semenza JC, Rubin CH, Falter KH, Selanikio JD, Flanders WD, Howe HL, Wilhelm JL |date=July 1996 |journal=New England Journal of Medicine |volume=335 |issue=2 |pages=84–90 |pmid=8649494 |doi=10.1056/NEJM199607113350203 |url=http://rcin.org.pl/Content/40952|doi-access=free }}</ref>

===Drugs===
Some drugs cause excessive internal heat production.<ref name=Harrisons /> The rate of drug-induced hyperthermia is higher where use of these drugs is higher.<ref name=Harrisons />
* Many psychotropic medications, such as [[selective serotonin reuptake inhibitors]] (SSRIs), [[monoamine oxidase inhibitors]] (MAOIs), and [[tricyclic antidepressants]], can cause hyperthermia.<ref name=Harrisons /> [[Serotonin syndrome]] is a rare adverse reaction to overdose of these medications or the use of several simultaneously. Similarly, [[neuroleptic malignant syndrome]] is an uncommon reaction to [[neuroleptic]] agents.<ref>{{cite book |title=Emergency Medicine: A Comprehensive Study Guide, Sixth edition |last=Tintinalli |first=Judith |year=2004 |publisher=McGraw-Hill Professional |isbn=0-07-138875-3 |page=1818}}</ref> These syndromes are differentiated by other associated symptoms, such as tremor in serotonin syndrome and "lead-pipe" muscle rigidity in neuroleptic malignant syndrome.<ref name=Harrisons />
* Recreational drugs such as [[amphetamines]]<ref>{{cite book |title=Rosen's emergency medicine: concepts and clinical practice |last=Marx |first=John |year=2006 |publisher=Mosby/Elsevier |isbn=978-0-323-02845-5 |page=2894 |url=https://archive.org/details/rosensemergencym0002unse |url-access=registration}}</ref> and [[cocaine]],<ref>{{cite book |title=Rosen's emergency medicine: concepts and clinical practice |last=Marx |first=John |year=2006 |publisher=Mosby/Elsevier |isbn=978-0-323-02845-5 |page=2388 |url=https://archive.org/details/rosensemergencym0002unse |url-access=registration}}</ref>  [[Phencyclidine|PCP]], [[dextromethorphan]], [[LSD]], and [[MDMA]] may cause hyperthermia.<ref name=Harrisons />
* [[Malignant hyperthermia]] is a rare reaction to common anesthetic agents (such as [[halothane]]) or the paralytic agent [[succinylcholine]]. Those who have this reaction, which is potentially fatal, have a genetic predisposition.<ref name=Harrisons />
* The use of [[anticholinergic]]s, more specifically [[muscarinic antagonist]]s are thought to cause mild hyperthermic episodes due to its parasympatholytic effects. The sympathetic nervous system, also known as the "[[fight-or-flight response]]", dominates by raising catecholamine levels by the blocked action of the "rest and digest system".<ref>{{cite news|last=Patel|first=R.J.|pmid=14751484|title=Prevalence of autonomic signs and symptoms in antimuscarinic drug poisonings|journal=J. Emerg. Med.|date=January 2004|volume=26|number=1|pages=89–94|display-authors=etal}}</ref>
* Drugs that decouple [[oxidative phosphorylation]] may also cause hyperthermia. From this group of drugs the most well-known is [[2,4-Dinitrophenol|2,4-dinitrophenol]] which was used as a weight loss drug until dangers from its use became apparent.

===Personal protective equipment===
Those working in industry, in the military, or as [[Certified first responder|first responder]]s may be required to wear [[personal protective equipment]] (PPE) against hazards such as chemical agents, gases, fire, small arms and [[improvised explosive device]]s (IEDs). PPE includes a range of [[hazmat suit]]s, firefighting [[bunker gear|turnout gear]], body armor and [[bomb suit]]s, among others. Depending on design, the wearer may be encapsulated in a microclimate,<ref name=MicroclimateCooling>{{cite web |title=Microclimate Conditioning Systems |publisher=US Army Natick Soldier RD&E Center |url=http://nsrdec.natick.army.mil/media/print/MCC_Systems_Trifold.pdf |date=May 2007 |access-date=2 August 2015 |archive-date=17 August 2016 |archive-url=https://web.archive.org/web/20160817130306/http://nsrdec.natick.army.mil/media/print/MCC_Systems_Trifold.pdf |url-status=dead }}</ref> due to an increase in thermal resistance and decrease in vapor permeability. As physical work is performed, the body's natural thermoregulation (i.e. sweating) becomes ineffective. This is compounded by increased work rates, high ambient temperature and humidity levels, and direct exposure to the sun. The net effect is that desired protection from some environmental threats inadvertently increases the threat of heat stress.

The effect of PPE on hyperthermia has been noted in fighting the [[Ebola virus epidemic in West Africa|2014 Ebola virus epidemic]] in Western Africa. Doctors and healthcare workers were only able to work for 40 minutes at a time in their protective suits, fearing heat stroke.<ref>{{cite news |url=https://www.npr.org/2014/10/07/354230895/ebola-protective-suits-are-in-short-supply |title=Ebola Protective Suits Are In Short Supply |first=Jackie |last=Northam |publisher=National Public Radio |date=7 October 2014 |access-date=21 January 2015}}</ref>

===Other===
Other rare causes of hyperthermia include [[thyrotoxicosis]] and an [[adrenal gland]] tumor, called [[pheochromocytoma]], both of which can cause increased heat production.<ref name=Harrisons /> Damage to the central nervous system from brain hemorrhage, traumatic brain injury, [[status epilepticus]], and other kinds of injury to the hypothalamus can also cause hyperthermia.<ref name=Harrisons />

==Pathophysiology==
[[File:fever-conceptual.svg|thumb|upright=1.6|A summary of the differences between hyperthermia, [[hypothermia]], and fever.<br />Hyperthermia: Characterized on the left. Normal body temperature (thermoregulatory set-point) is shown in green, while the hyperthermic temperature is shown in red. As can be seen, hyperthermia can be considered an increase above the thermoregulatory set-point.<br />Hypothermia: Characterized in the center: Normal body temperature is shown in green, while hypothermic temperature is shown in blue. As can be seen, hypothermia can be conceptualized as a decrease below the thermoregulatory set-point.<br />Fever: Characterized on the right: Normal body temperature is shown in green. It reads "New Normal" because the thermoregulatory set-point has risen. This has caused what was the normal body temperature (in blue) to be considered hypothermic.]]

A [[fever]] occurs when the [[body temperature|core temperature]] is set higher, through the action of the pre-optic region of the [[anterior hypothalamus]]. For example, in response to a [[bacteria]]l or [[virus|viral]] infection, certain white blood cells within the blood will release [[pyrogens]] which have a direct effect on the anterior hypothalamus, causing body temperature to rise, much like raising the temperature setting on a [[thermostat]].

In contrast, hyperthermia occurs when the body temperature rises without a change in the heat control centers.

Some of the gastrointestinal symptoms of acute exertional heatstroke, such as vomiting, diarrhea, and gastrointestinal bleeding, may be caused by barrier dysfunction and subsequent [[endotoxemia]]. Ultraendurance athletes have been found to have significantly increased plasma endotoxin levels. Endotoxin stimulates many inflammatory cytokines, which in turn may cause multiorgan dysfunction. Experimentally, monkeys treated with oral antibiotics prior to induction of heat stroke do not become endotoxemic.<ref>Lambert, Patrick. "Role of gastrointestinal permeability in exertional heatstroke". ''Exercise and Sport Science Reviews.'' '''32'''(4): 185-190. 2004</ref>

There is scientific support for the concept of a temperature set point; that is, maintenance of an optimal temperature for the metabolic processes that life depends on. Nervous activity in the [[Preoptic area|preoptic-anterior hypothalamus]] of the brain triggers heat losing (sweating, etc.) or heat generating (shivering and muscle contraction, etc.) activities through stimulation of the autonomic nervous system. The pre-optic anterior hypothalamus has been shown to contain warm sensitive, cool sensitive, and temperature insensitive neurons, to determine the body's temperature setpoint. As the temperature that these neurons are exposed to rises above {{cvt|37|C}}, the rate of electrical discharge of the warm-sensitive neurons increases progressively. Cold-sensitive neurons increase their rate of electrical discharge progressively below {{cvt|37|C}}.<ref>{{cite web|last=Byrne|first=J.H.|title=Neuroscience Online: An Electronic Textbook for the Neurosciences|url=http://nba.uth.tmc.edu/neuroscience/|publisher=Department of Neurobiology and Anatomy, The University of Texas Medical School at Houston (UTHealth)|access-date=13 January 2013}}</ref>

==Diagnosis==
Hyperthermia is generally diagnosed by the combination of unexpectedly high body temperature and a history that supports hyperthermia instead of a fever.<ref name=Harrisons /> Most commonly this means that the elevated temperature has occurred in a hot, humid environment (heat stroke) or in someone taking a drug for which hyperthermia is a known side effect (drug-induced hyperthermia). The presence of signs and symptoms related to hyperthermia syndromes, such as extrapyramidal symptoms characteristic of neuroleptic malignant syndrome, and the absence of signs and symptoms more commonly related to infection-related fevers, are also considered in making the diagnosis.

If [[antipyretic|fever-reducing drugs]] lower the body temperature, even if the temperature does not return entirely to normal, then hyperthermia is excluded.<ref name=Harrisons />

==Prevention==
When ambient temperature is excessive, humans and many other animals cool themselves below ambient by [[evaporative cooling]] of [[sweat]] (or other aqueous liquid; [[saliva]] in dogs, for example); this helps prevent potentially fatal hyperthermia. The effectiveness of evaporative cooling depends upon [[humidity]]. [[Wet-bulb temperature#Wet-bulb temperature and health|Wet-bulb temperature]], which takes humidity into account, or more complex calculated quantities such as [[wet-bulb globe temperature]] (WBGT), which also takes [[solar radiation]] into account, give useful indications of the degree of heat stress and are used by several agencies as the basis for heat-stress prevention guidelines. (Wet-bulb temperature is essentially the lowest skin temperature attainable by evaporative cooling at a given ambient temperature and humidity.)

A sustained wet-bulb temperature exceeding {{convert|35|C|F}} is likely to be fatal even to fit and healthy people unclothed in the shade next to a fan; at this temperature, environmental heat gain instead of loss occurs. {{As of|2012}}, wet-bulb temperatures only very rarely exceeded {{convert|30|C|F}} anywhere, although significant [[global warming]] may change this.<ref>{{cite journal |title=Thermogeddon: Too hot for humans |first=Hazel |last=Muir |journal=New Scientist |volume=208 |issue=2783 |pages=36–39 |doi=10.1016/S0262-4079(10)62649-8 |date=23 October 2010 |bibcode=2010NewSc.208...36M }}<!--|access-date=2 August 2015--></ref><ref>{{Cite web|last=Madge|first=Grahame|date=2021-11-09|title=One billion face heat-stress risk from 2°C rise|url=https://www.metoffice.gov.uk/about-us/press-office/news/weather-and-climate/2021/2c-rise-to-put-one-in-eight-of-global-population-at-heat-stress-risk|access-date=2021-11-10|website=Met Office|language=en}}</ref>

In cases of heat stress caused by physical exertion, hot environments, or protective equipment, prevention or mitigation by frequent rest breaks, careful hydration, and monitoring body temperature should be attempted.<ref>{{cite web|title=NIOSH Workplace Safety and Health Topics: Heat Stress|url=https://www.cdc.gov/niosh/topics/heatstress/|publisher=National Institute for Occupational Safety and Health|access-date=21 March 2014}}</ref> However, in situations demanding one is exposed to a hot environment for a prolonged period or must wear protective equipment, a personal cooling system is required as a matter of health and safety. There are a variety of active or passive personal cooling systems;<ref name=MicroclimateCooling/> these can be categorized by their power sources and whether they are person- or vehicle-mounted.

Because of the broad variety of operating conditions, these devices must meet specific requirements concerning their rate and duration of cooling, their power source, and their adherence to health and safety regulations. Among other criteria are the user's need for physical mobility and autonomy. For example, active-liquid systems operate by chilling water and circulating it through a garment; the skin surface area is thereby cooled through conduction. This type of system has proven successful in certain military, law enforcement, and industrial applications. Bomb-disposal technicians wearing special suits to protect against improvised explosive devices (IEDs) use a small, ice-based chiller unit that is strapped to one leg; a liquid-circulating garment, usually a vest, is worn over the torso to maintain a safe core body temperature. By contrast, soldiers traveling in combat vehicles can face microclimate temperatures in excess of {{cvt|65|C}} and require a multiple-user, vehicle-powered cooling system with rapid connection capabilities. Requirements for hazmat teams, the medical community, and workers in heavy industry vary further.

==Treatment==
The underlying cause must be removed. Mild hyperthemia caused by exertion on a hot day may be adequately treated through self-care measures, such as increased [[water consumption]] and resting in a cool place. Hyperthermia that results from [[drug]] exposure requires prompt cessation of that drug, and occasionally the use of other drugs as counter measures.

[[Antipyretics]] (e.g., [[acetaminophen]], [[aspirin]], other [[nonsteroidal anti-inflammatory drugs]]) have no role in the treatment of [[heatstroke]] because antipyretics interrupt the change in the [[hypothalamic]] [[Setpoint (control system)|set point]] caused by [[pyrogens]]; they are not expected to work on a healthy [[hypothalamus]] that has been overloaded, as in the case of heatstroke. In this situation, antipyretics actually may be harmful in patients who develop [[hepatic]], [[hematologic]], and [[renal]] [[Complication (medicine)|complications]] because they may aggravate [[bleeding]] tendencies.<ref>{{EMedicine|article|166320|Heatstroke|treatment}}</ref>

When body temperature is significantly elevated, mechanical cooling methods are used to remove heat and to restore the body's ability to regulate its own temperatures.<ref name=Harrisons /> Passive cooling techniques, such as resting in a cool, shady area and removing clothing can be applied immediately. Active cooling methods, such as sponging the head, neck, and [[Trunk (anatomy)|trunk]] with cool water, remove heat from the body and thereby speed the body's return to normal temperatures. When methods such as immersion are impractical, misting the body with water and using a fan have also been shown to be effective.<ref>{{Citation |last1=Wasserman |first1=Deena D. |title=Cooling Techniques for Hyperthermia |date=2023 |url=http://www.ncbi.nlm.nih.gov/books/NBK459311/ |work=StatPearls |access-date=2023-09-02 |place=Treasure Island (FL) |publisher=StatPearls Publishing |pmid=29083764 |last2=Creech |first2=Julie A. |last3=Healy |first3=Megan}}</ref>

Sitting in a bathtub of tepid or cool water (immersion method) can remove a significant amount of heat in a relatively short period of time. It was once thought that immersion in very cold water is counterproductive, as it causes [[vasoconstriction]] in the skin and thereby prevents heat from escaping the body core. However, a British analysis of various studies stated: "this has never been proven experimentally. Indeed, a recent study using normal volunteers has shown that cooling rates were fastest when the coldest water was used."<ref name="ReferenceA">{{cite journal |last1=Smith |first1=J E |title=Cooling methods used in the treatment of exertional heat illness |journal=British Journal of Sports Medicine |volume=39 |issue=8 |pages=503–7; discussion 507 |year=2005 |pmid=16046331 |pmc=1725271 |doi=10.1136/bjsm.2004.013466 }}</ref> The analysis concluded that iced water immersion is the most-effective cooling technique for exertional heat stroke.<ref name="ReferenceA"/> No superior cooling method has been found for ''non-exertional heat stroke''.<ref>{{cite journal |last1=Bouchama |first1=Abderrezak |last2=Dehbi |first2=Mohammed |last3=Chaves-Carballo |first3=Enrique |title=Cooling and hemodynamic management in heatstroke: practical recommendations |journal=Critical Care |volume=11 |issue=3 |pages=R54 |year=2007 |pmid=17498312 |pmc=2206402 |doi=10.1186/cc5910 |doi-access=free }}</ref> Thus, aggressive ''ice-water'' immersion remains the gold standard for ''life-threatening heat stroke''.<ref>{{cite journal |journal=Exerc Sport Sci Rev |date=July 2007 |volume=35 |issue=3 |pages=141–149 |title=Cold water immersion: the gold standard for exertional heatstroke treatment |vauthors=Casa DJ, McDermott BP, Lee EC, Yeargin SW, Armstrong LE, Maresh CM |pmid=17620933 |doi=10.1097/jes.0b013e3180a02bec|s2cid=29436184 |doi-access=free }}</ref><ref>{{cite journal |doi=10.4085/1062-6050-44.1.84 |title=Acute Whole-Body Cooling for Exercise-Induced Hyperthermia: A Systematic Review |year=2009 |last1=McDermott |first1=Brendon P. |last2=Casa |first2=Douglas J. |last3=Ganio |first3=Matthew S. |last4=Lopez |first4=Rebecca M. |last5=Yeargin |first5=Susan W. |last6=Armstrong |first6=Lawrence E. |last7=Maresh |first7=Carl M. |journal=Journal of Athletic Training |volume=44 |pages=84–93 |pmid=19180223 |issue=1 |pmc=2629045}}</ref>

When the body temperature reaches about {{convert|40|C|F}}, or if the affected person is unconscious or showing signs of confusion, hyperthermia is considered a [[medical emergency]] that requires treatment in a proper medical facility. A [[Cardiopulmonary resuscitation#Compressions with rescue breaths|cardiopulmonary resuscitation]] (CPR) may be necessary if the person goes into [[cardiac arrest]] (stop of heart beats). Already in a hospital, more aggressive cooling measures are available, including [[intravenous]] [[Fluid replacement|hydration]], [[gastric lavage]] with iced [[Saline water|saline]], and even [[hemodialysis]] to cool the blood.<ref name=Harrisons />

==Epidemiology== <!-- see similar section in Heat stroke -->
Hyperthermia affects those who are unable to regulate their body heat, mainly due to environmental conditions. The main risk factor for hyperthermia is the lack of ability to sweat. People who are dehydrated or who are older may not produce the sweat they need to regulate their body temperature.<ref>{{Cite journal|last1=Cramer|first1=Matthew N.|last2=Jay|first2=Ollie|date=2016-04-01|title=Biophysical aspects of human thermoregulation during heat stress|journal=Autonomic Neuroscience|series=SI:Thermoregulation|volume=196|pages=3–13|doi=10.1016/j.autneu.2016.03.001|pmid=26971392|s2cid=3779953|issn=1566-0702}}</ref> High heat conditions can put certain groups at risk for hyperthermia including: physically active individuals, soldiers, construction workers, landscapers and factory workers. Some people that do not have access to cooler living conditions, like people with lower socioeconomic status, may have a difficult time fighting the heat. People are at risk for hyperthermia during high heat and dry conditions, most commonly seen in the summer.

Various cases of different types of hyperthermia have been reported. A research study was published in March 2019 that looked into multiple case reports of drug induced hyperthermia. The study concluded that psychotropic drugs such as anti-psychotics, antidepressants, and anxiolytics were associated with an increased heat-related mortality as opposed to the other drugs researched (anticholinergics, diuretics, cardiovascular agents, etc.).<ref>{{Cite journal|last1=Bongers|first1=Koen Sebastiaan|last2=Salahudeen|first2=Mohammed S.|last3=Peterson|first3=Gregory M.|date=2019-10-23|title=Drug-associated non-pyrogenic hyperthermia: a narrative review|journal=European Journal of Clinical Pharmacology|volume=76|issue=1|pages=9–16|doi=10.1007/s00228-019-02763-5|pmid=31642960|s2cid=204835523|issn=0031-6970}}</ref> A different study was published in June 2019 that examined the association between hyperthermia in older adults and the temperatures in the United States. Hospitalization records of elderly patients in the US between 1991 and 2006 were analyzed and concluded that cases of hyperthermia were observed to be highest in regions with arid climates. The study discussed finding a disproportionately high number of cases of hyperthermia in early seasonal heat waves indicating that people were not yet practicing proper techniques to stay cool and prevent overheating in the early presence of warm, dry weather.<ref>{{Cite journal|last1=Liss|first1=Alexander|last2=Naumova|first2=Elena N.|date=2019|title=Heatwaves and hospitalizations due to hyperthermia in defined climate regions in the conterminous USA|journal=Environmental Monitoring and Assessment|volume=191|issue=S2|pages=394|doi=10.1007/s10661-019-7412-5|pmid=31254102|bibcode=2019EMnAs.191S.394L |s2cid=195761385|issn=0167-6369}}</ref>

In urban areas people are at an increased susceptibility to hyperthermia. This is due to a phenomenon called the [[Urban heat island|urban heat island effect]].<ref>{{Cite journal|last1=Basu|first1=Rupa|last2=Samet|first2=Jonathan M.|date=2002-12-01|title=Relation between Elevated Ambient Temperature and Mortality: A Review of the Epidemiologic Evidence|url=https://academic.oup.com/epirev/article/24/2/190/535042|journal=Epidemiologic Reviews|volume=24|issue=2|pages=190–202|doi=10.1093/epirev/mxf007|pmid=12762092|issn=0193-936X|doi-access=free}}</ref> Since the 20th century in the United States, the north-central region (Ohio, Indiana, Illinois, Missouri, Iowa, and Nebraska) was the region with the highest morbidity resulting from hyperthermia. Northeastern states had the next highest. Regions least affected by heat wave-related hyperthermia causing death were Southern and Pacific Coastal states.<ref>{{Cite journal|last=Gover|first=Mary|date=1938|title=Mortality during Periods of Excessive Temperature|journal=Public Health Reports |volume=53|issue=27|pages=1122–1143|doi=10.2307/4582590|issn=0094-6214|jstor=4582590}}</ref> Northern cities in the United States are at greater risk of hyperthermia during heat waves due to the fact that people tend to have a lower minimum mortality temperature at higher latitudes.<ref name=":0">{{Cite journal|last1=Curriero |first1=Frank C. |last2=Heiner |first2=Karlyn S. |last3=Samet |first3=Jonathan M. |last4=Zeger |first4=Scott L. |last5=Strug |first5=Lisa |last6=Patz |first6=Jonathan A. |date=2002-01-01|title=Temperature and Mortality in 11 Cities of the Eastern United States|url=https://academic.oup.com/aje/article/155/1/80/134292|journal=American Journal of Epidemiology|volume=155|issue=1|pages=80–87|doi=10.1093/aje/155.1.80|pmid=11772788|issn=0002-9262 |quote=The authors also found a strong association of the temperature-mortality relation with latitude, with a greater effect of colder temperatures on mortality risk in more-southern cities and of warmer temperatures in more-northern cities.|doi-access=free }}</ref> In contrast, cities residing in lower latitudes within the continental US typically have higher thresholds for ambient temperatures.<ref name=":0" /> In India, hundreds die every year from summer heat waves,<ref>{{cite news |url=http://www.indiaspend.com/cover-story/61-rise-in-heat-stroke-deaths-over-decade-60404 |title=61% Rise In Heat-Stroke Deaths Over Decade |first=Chaitanya |last=Mallapur |publisher=IndiaSpend |date=27 May 2015 |access-date=26 June 2015 |archive-date=29 June 2015 |archive-url=https://web.archive.org/web/20150629084810/http://www.indiaspend.com/cover-story/61-rise-in-heat-stroke-deaths-over-decade-60404 |url-status=dead }}</ref> including [[2015 Indian heat wave|more than 2,500 in the year 2015]].<ref>{{cite news |url=https://www.telegraph.co.uk/news/worldnews/asia/india/11645731/India-heatwave-death-toll-passes-2500-as-victim-families-fight-for-compensation.html |archive-url=https://ghostarchive.org/archive/20220112/https://www.telegraph.co.uk/news/worldnews/asia/india/11645731/India-heatwave-death-toll-passes-2500-as-victim-families-fight-for-compensation.html |archive-date=12 January 2022 |url-access=subscription |url-status=live |title=India heatwave: death toll passes 2,500 as victim families fight for compensation |agency=Reuters |date=2 June 2015 |access-date=26 June 2015}}{{cbignore}}</ref> Later that same summer, the [[2015 Pakistani heat wave]] killed about 2,000 people.<ref>{{cite news |url=https://www.bloomberg.com/news/articles/2015-06-24/heat-wave-death-toll-rises-to-2-000-in-pakistan-s-financial-hub |title=Heat Wave Death Toll Rises to 2,000 in Pakistan's Financial Hub |first1=Kamran |last1=Haider |first2=Khurrum |last2=Anis |publisher=Bloomberg News |date=24 June 2015 |access-date=3 August 2015}}</ref> An extreme [[2003 European heat wave]] caused tens of thousands of deaths.<ref>{{cite journal |doi=10.1016/j.crvi.2007.12.001 |issn=1631-0691 |last=Robine |first=Jean-Marie |display-authors=etal |title=Death toll exceeded 70,000 in Europe during the summer of 2003 |journal=Comptes Rendus Biologies |volume=331 |issue=2 |pages=171–178 |date=February 2008 |pmid=18241810 |url=https://comptes-rendus.academie-sciences.fr/biologies/articles/10.1016/j.crvi.2007.12.001/ }}</ref>

Causes of hyperthermia include dehydration, use of certain medications, using cocaine and amphetamines or excessive alcohol use.<ref name=":1">{{Cite journal|last1=Walter|first1=Edward James|last2=Carraretto|first2=Mike|date=2016|title=The neurological and cognitive consequences of hyperthermia|journal=Critical Care|volume=20|issue=1|pages=199|doi=10.1186/s13054-016-1376-4|issn=1364-8535|pmc=4944502|pmid=27411704 |doi-access=free }}</ref> Bodily temperatures greater than {{convert|37.5|–|38.3|C|F}} can be diagnosed as a hyperthermic case.<ref name=":1" /> As body temperatures increase or excessive body temperatures persist, individuals are at a heightened risk of developing progressive conditions. Greater risk complications of hyperthermia include heat stroke, organ malfunction, organ failure, and death. There are two forms of [[heat stroke]]; classical heatstroke and exertional heatstroke. Classical heatstroke occurs from extreme environmental conditions, such as heat waves. Those who are most commonly affected by classical heatstroke are very young, elderly or chronically ill. Exertional heatstroke appears in individuals after vigorous physical activity. Exertional heatstroke is displayed most commonly in healthy 15-50 year old people. Sweating is often present in exertional heatstroke.<ref>{{Citation|last1=Leon|first1=Lisa R.|title=Heat Stroke|volume=5|issue=2|date=2015|journal=Comprehensive Physiology|pages=611–647|publisher=American Cancer Society|language=en|doi=10.1002/cphy.c140017|pmid=25880507|isbn=978-0-470-65071-4|last2=Bouchama|first2=Abderrezak|url=https://zenodo.org/record/1229151}}</ref> The associated mortality rate of heatstroke is 40 to 64%.<ref name=":1" />

==Research==
Hyperthermia can also be [[hyperthermia therapy|deliberately induced]] using drugs or medical devices, and is being studied and applied in clinical routine as a treatment of some kinds of [[cancer]].<ref>{{cite web |url=http://www.cancer.gov/cancertopics/factsheet/Therapy/hyperthermia |title=Hyperthermia in Cancer Treatment |publisher=[[National Cancer Institute]] |date=31 August 2011 |access-date=2 August 2015}}</ref> Research has shown that medically controlled hyperthermia can shrink tumours.<ref name="Jha 161–167">{{Cite journal |last1=Jha |first1=Sheetal |last2=Sharma |first2=Pramod Kumar |last3=Malviya |first3=Rishabha |date=2016-12-01 |title=Hyperthermia: Role and Risk Factor for Cancer Treatment |journal=Achievements in the Life Sciences |language=en |volume=10 |issue=2 |pages=161–167 |doi=10.1016/j.als.2016.11.004 |issn=2078-1520|doi-access=free }}</ref><ref>{{Cite journal |last1=Wust |first1=P |last2=Hildebrandt |first2=B |last3=Sreenivasa |first3=G |last4=Rau |first4=B |last5=Gellermann |first5=J |last6=Riess |first6=H |last7=Felix |first7=R |last8=Schlag |first8=PM |date=2002-08-01 |title=Hyperthermia in combined treatment of cancer |url=https://doi.org/10.1016/S1470-2045(02)00818-5 |journal=The Lancet Oncology |volume=3 |issue=8 |pages=487–497 |doi=10.1016/s1470-2045(02)00818-5 |pmid=12147435 |issn=1470-2045}}</ref> This occurs when a high body temperature damages cancerous cells by destroying proteins and structures within each cell.<ref>{{Cite journal |last1=van der Zee |first1=Jacoba |last2=González |first2=Dionisio |last3=van Rhoon |first3=Gerard C |last4=van Dijk |first4=Jan DP |last5=van Putten |first5=Wim LJ |last6=Hart |first6=Augustinus AM |date=2000-04-01 |title=Comparison of radiotherapy alone with radiotherapy plus hyperthermia in locally advanced pelvic tumours: a prospective, randomised, multicentre trial |url=https://doi.org/10.1016/S0140-6736(00)02059-6 |journal=The Lancet |volume=355 |issue=9210 |pages=1119–1125 |doi=10.1016/s0140-6736(00)02059-6 |pmid=10791373 |s2cid=25518938 |issn=0140-6736}}</ref><ref name="Jha 161–167"/> Hyperthermia has also been researched to investigate whether it causes cancerous tumours to be more prone to radiation as a form of treatment; which as a result has allowed hyperthermia to be used to complement other forms of cancer therapy.<ref>{{Cite journal |last=Alexander |first=H. R. |date=2001-01-01 |title=Isolation perfusion. |journal=Cancer: Principles and Practice of Oncology |volume=1 |pages=2}}</ref><ref name="Jha 161–167"/> Various techniques of hyperthermia in the treatment of cancer include local or regional hyperthermia, as well as whole body techniques.<ref name="Jha 161–167"/>

==See also==
* [[Effects of climate change on human health]]
* {{annotated link|Hot flash}}
* {{annotated link|Occupational heat stress}}
* {{annotated link|Rhabdomyolysis}}
* [[Space blanket]]

==References==
{{Reflist|colwidth=30em}}

==External links==
* [http://www.redcross.org/news/press-release/American-Red-Cross-Tips-to-Beat-the-Heat Tips to Beat the Heat] {{Webarchive|url=https://web.archive.org/web/20140721024528/http://www.redcross.org/news/press-release/American-Red-Cross-Tips-to-Beat-the-Heat |date=21 July 2014 }}—[[American Red Cross]]
* [http://emergency.cdc.gov/disasters/extremeheat/ Extreme Heat]—CDC Emergency Preparedness and Response
* [https://www.cdc.gov/niosh/topics/heatstress/ Workplace Safety and Health Topics: Heat Stress]—CDC and [[National Institute for Occupational Safety and Health|NIOSH]]
* ''[http://www.epa.gov/hiri/about/pdf/EHEguide_final.pdf Excessive Heat Events Guidebook]''—US EPA
* [http://books.nap.edu/openbook.php?record_id=2094&page=55 Physiological Responses to Exercise in the Heat]—US National Academies

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[[Category:Deaths from hyperthermia| ]]
[[Category:Causes of death]]
[[Category:Heat waves]]
[[Category:Medical emergencies]]
[[Category:Weather and health]]
[[Category:Physiology]]
[[Category:Thermoregulation]]