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Hypothermia is a medical condition in which the victim's core body temperature has dropped to significantly below normal and normal metabolism begins to be impaired. This begins to occur when the core temperature drops below 35 degrees Celsius (95 degrees Fahrenheit). If body temperature falls below 32 °C (90 °F), the condition can become critical and eventually fatal. Body temperatures below 27 °C (80 °F) are almost uniformly fatal, though body temperatures as low as 14 °C (57.5 °F) have been known to survive. The opposite condition, where temperature is too high, is hyperthermia. more...

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For unknown reasons, people who fall critically unconscious (and arguably die, though there are some who argue that any reversible condition is not, by definition, death) in very cold water can, in rare cases, be resuscitated, even though they would be expected to have died of drowning and/or hypothermia. See Mammalian diving reflex.


There are three types of hypothermia, acute, subacute, and chronic.

  • Acute hypothermia is the most dangerous; the body temperature drops very swiftly, often in a matter of seconds or minutes, such as when a victim falls through an ice-covered lake.
  • Subacute hypothermia occurs on a scale of hours, most commonly by remaining in a cold environment for an extended period of time.
  • Chronic hypothermia is typically caused by an underlying disease.


  • Amnesia
  • Ataxia
  • Cold skin, even in torso
  • Confusion, progressing to delirium
  • Diuresis
  • Dysarthria
  • Gray complexion (pallor)
  • Hypokinesia
  • Increased muscle tone
  • Low blood pressure (hypotension)
  • Peripheral cyanosis
  • Rapid breathing (tachypnea) and heart rate (tachycardia), slowing and weakening as temperature decreases
  • Shivering
  • Tremor
  • Uncontrollable bleeding due to reduced coagulation enzyme activity
  • Weakness


Treatment for hypothermia involves raising the core body temperature of the victim.

The first aid response to someone experiencing hypothermia, however, must be made with caution.

  • Do not rub or massage the casualty
  • Do not give alcohol
  • Do not treat any frostbite
  • Do not allow the body to become vertical

Any of these actions will divert blood from the critical internal organs and will worsen the situation.

What you should do:

  • Call the emergency services
  • Get the patient to shelter
  • If possible, put the patient in a bath with medium-temperature water, with the clothes on
  • Place hot water bottles (wrapped in a cotton sock) in the patient's armpits and between their legs
  • Give food and warm drinks
  • Monitor the patient and be prepared to give Cardio-pulmonary resuscitation.
  • Remove wet clothing if and only if a dry change is available

If the hypothermia has become severe, notably if the patient is incoherent or unconscious, re-warming must be done under strictly controlled circumstances in a hospital. Bystanders should only remove the patient from the cold environment, give warm drinks (not too warm because it can lead to temperature shock) and get the patient to advanced medical care as quickly as possible.


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Hypothermia-related deaths—Philadelphia, 2001, and United States, 1999
From Morbidity and Mortality Weekly Report, 2/7/03

Hypothermia is defined as the unintentional lowering of the deep body (core) temperature below 95.0 [degrees] F (35.0[degrees] C). Hypothermia can be mild (90.0[degrees] F-<95.0[degrees] F [32.2[degrees] C-<35.0[degrees] C]), moderate (82.5[degrees] F-.<90.0[degrees] F [28.00 C-<32.2[degrees] C]), or severe (<82.5[degrees] F [<28.0[degrees] C]). Common risk factors for hypothermia include exposure to cold while under the influence of alcohol or drugs, altered mental status, and immersion in cold water (1). During 1979-1998, approximately 700 persons (range: 420-1,024) died annually in the United States from hypothermia; approximately half of these deaths were attributed to extremely cold weather (2). This report presents three cases of hypothermia-related deaths in Philadelphia during 2001 as examples of risk factors for hypothermia and summarizes information about hypothermia-related deaths in the United States during 1999. Hypothermia deaths are preventable; by avoiding hypothermia, persons also can prevent other adverse health effects of cold weather.

Case Reports

Case 1. In January 2001, a man aged 60 years was found dead by police; he was lying on a sofa inside an abandoned house that had no heat or electricity. Other inhabitants in the house reported that the man had been drinking alcohol before his death. During the 24 hours before the man was found, the minimum temperature was 21.0[degrees] F (-6.0[degrees] C). On autopsy, the man was found to have a blood alcohol concentration (BAC) of 0.23 g/dL; in Pennsylvania, drivers are considered intoxicated if their BAC is [greater than or equal to]0.10 g/dL.

Case 2. In January 2001, paramedics were called to assist a man aged 25 years who was found unresponsive on a sidewalk late at night. The low temperature during the previous 24 hours was 31.0[degrees] F (-0.6[degrees] C). The man was transported to a hospital, where he was resuscitated through advanced cardiac life support protocol. He remained in a vegetative state and died 9 days later. His BAC at the time of admission was 0.48 g/dL; the underlying cause of death was listed as acute alcohol intoxication, with hypothermia as a contributing factor.

Case 3. In February 2001, a woman aged 48 years was found collapsed along a roadside. During the previous day, approximately 2 inches of snow had fallen, and the minimum ambient temperature had been 29.0[degrees] F (1.6[degrees] C). After transport to a hospital, her core body temperature was 91.5[degrees] F (33.0[degrees] C). The woman died despite extensive efforts at resuscitation, including intravenous infusion and peritoneal lavage with warmed fluids. Autopsy revealed bilateral pneumonia and positive blood toxicology for morphine and diphenhydramine. Sepsis was listed as the primary cause of death, with hypothermia as a contributing factor.

United States

Since 1999, CDC's National Center for Health Statistics (NCHS) has used information from death certificates categorized with International Classification of Diseases, Tenth Revision (ICD-10) codes to estimate national mortality trends. During 1999, exposure to excessive natural cold (ICD-10 code X31) was listed as the underlying cause of death (i.e., the circumstance of the accident that produced the fatal injury) for 598 persons in the United States (Figure), and hypothermia (ICD-10 code T68) was listed as a nature of injury (i.e., an injury that occurred to the decedent) in 1,139 deaths (2). Of the 598 hypothermia-related deaths, 380 (64%) occurred among males, and 359 (60%) of the 597 persons who died of hypothermia and whose age was known were aged [greater than or equal to]65 years. During 1999, Pennsylvania and New York had the greatest number of hypothermia-related deaths (36 each) (2), and Alaska had the highest crude death rate (1.9 per 100,000 population), approximately twice that of Montana, which had second-highest rate (0.9).

Reported by: H Mirchandani, MD, Medical Examiners Office; C Johnson, MD, Div of Disease Control, Philadelphia Dept of Public Health, Pennsylvania. Div of Environmental Hazards and Health Effects, National Center for Environmental Health; C Newbern, PhD, C Sanchez, MD, EIS Officers, CDC.

Editorial Note: Hypothermia is an important cause of preventable deaths in the United States, especially among persons who abuse alcohol (3). Ethanol causes vasodilation, which produces a brief "warming" sensation that interferes with peripheral vasoconstriction, the physiological defense against cold, while also inducing hypoglycemia. Alcohol consumption in cold surroundings is a dangerous practice. Unattended children and persons aged >65 years also are at greater risk for hypothermia (3).

Hypothermia during cold weather is the result of decreased heat production, increased heat loss, or impaired thermoregulation (1). Older persons, who have a decreased basal metabolic rate, might be at further risk for hypothermia because of impaired physical exertion, which produces heat to keep the body warm (4). Inactivity limits heat production through physical exertion, but overexertion can increase evaporation from the respiratory tract and cause fatigue. Shivering also can cause enough lactate generation eventually to produce acidosis and fatigue. Exposure to high winds can further increase heat loss. As body temperature decreases, the hypothalamus fails to compensate body temperature, and the central nervous system follows the progressive systemic depression of metabolism. Finally, metabolic impairment from alcoholism, malnutrition, hypothyroidism, or advanced age can cause poor endurance to cold (4).

Warning symptoms for hypothermia in adults include shivering, confusion, memory loss, drowsiness, exhaustion, fumbling hands, and slurred speech. In children, symptoms include bright red, cold skin and extreme low energy (5). Immersion in warm water is highly efficient in raising body temperature but might hinder cardiopulmonary resuscitation (CPR) and more invasive techniques if needed. Drinking warm, nonalcoholic beverages can help raise body temperature if the person is conscious (5). However, none of these procedures substitutes adequately for proper medical attention, and special care should be taken when handling and transporting a patient because skin can become numb and slough easily.

In the presence of severe hypothermia with cardiac arrest, CPR should be initiated on site and continued during transportation (5). Because of the protective effect that a low temperature might have on brain ischemia (especially if asphyxia has not preceded circulatory arrest), attempts at rewarming victims with severe hypothermia and cardiac arrest outside the hospital are not recommended (6). Core body temperature before rewarming might not be a good predictive factor for positive outcome, and persons with a core temperature as low as 59.0[degrees] F (15.0[degrees] C) have survived (1). The time between rescue and rewarming does not predict outcome (1); in the most extreme case, a boy aged 5 years recovered without apparent cerebral sequelae after 40 minutes of submersion in ice-cold water (7).

Overall death rates from all causes increase during winter (3); in addition to hypothermia, cold temperature is associated with excess mortality from ischemic heart disease (8) and cerebrovascular disease (9). Cold-induced vasoconstriction and later hemoconcentration can result in rupture of atheromatous plaques and arterial thrombosis. Cold temperature also can lower the immune system's resistance to respiratory infection, causing an increase in respiratory disease mortality (9).

Hypothermia-related morbidity is not exclusive to cold northern climates. Persons from regions with warmer winters might be at greater risk from the indirect effects of cold weather than persons from regions with colder and longer winters (9,10). However, geographic distributions might represent not only seasonal temperature variations but also socioeconomic status (which can limit access to controlled indoor temperature), cultural backgrounds (which can influence behavior toward individual protection from cold as well as outdoor activity), or populations with a higher proportion of elderly persons (10).

Persons should rake precautions to maintain body temperature both inside and outside during cold weather by heating the home (taking care to avoid carbon monoxide intoxication), especially at night, and by wearing properly insulated clothes while performing outdoor activities. The outer layer of clothing should be tightly woven and wind resistant. Inside layers of wool, silk, or polypropylene are preferred over cotton. Persistent shivering always is a signal to return indoors.



(1.) Lazar HL. The treatment of hypothermia. N Engl J Med 1997;337:1545-7.

(2.) National Center for Health Statistics. Compressed mortality file. Hyattsville, Maryland: U.S. Department of Health and Human Services, CDC, National Center for Health Statistics, 2002.

(3.) Kilbourne EM. Illness due to thermal extremes. In: Last JM, Wallace RB, eds. Public Health and Preventive Medicine, 13th ed. New York, New York: McGraw-Hill, 1992.

(4.) Danzl DF, Pozos RS. Accidental hypothermia. N Engl J Med 1994;331:1756-60.

(5.) CDC. Extreme cold: a prevention guide to promote your personal health and safety. Atlanta, Georgia: U.S. Department of Health and Human Services, CDC, 1996. Available at

(6.) Offenstadt G, Harries M, MacKenzie MA, Walpoth BH, Mattle HP, Althaus U. Accidental deep hypothermia. N Engl J Med 1998;338:1160-2.

(7.) Sibke H, Rod T, Brievik H, Link B. Survival after 40 minutes submersion without cerebral sequelae. Lancet 1975;1:1275-7.

(8.) Seretakis D, Lagiou P, Lipworth L, et al. Changing seasonality of mortality from coronary heart disease. JAMA 1997;278:1012-4.

(9.) The Eurowinter Group. Cold exposure and winter mortality from ischaemic heart disease, cerebrovascular disease, respiratory disease, and all causes in warm and cold regions of Europe. Lancet 1997;349:1341-6.

(10.) Curriero FC, Heiner KS, Samet JM, Zeger SL, Strug L, Patz JA. Temperature and mortality in 11 cities of the eastern United States. Am J Epidemiol 2002;155:80-7.

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