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Perspectives in Disease Prevention and Health Promotion Hypothermia-Associated Deaths -- United States, 1968-1980

Mortality data from the National Center for Health Statistics show that, during the 13-year period from 1968 to 1980, 6,460 deaths were attributed to the effects of cold. The risk of death from hypothermia varies by both age and sex (Table 1). After the first year of life, death rates increase with age; elderly persons are at highest risk of mortality. A clear differential exists between the sexes, with the rates for males exceeding those for females for all but one age group. This differential is largest for persons 10-14 years of age, when males are almost nine times more likely to die from hypothermia. For this period, the age-adjusted mortality rate (deaths per million persons) for males was 4.2, compared with 1.0 for women. Reported by Div of Environmental Hazards and Health Effects, Center for Environmental Health, CDC.

Editorial Note

Editorial Note: Since hypothermia is an important cause of mortality in the United States during the winter season, and recent reports indicate that mortality rates have increased (1,2), physicians should be familiar with the diagnostic criteria and risk factors for hypothermia.

Hypothermia is defined as a lowering of core body temperature to 35 C (95 F) or below. The severity of hypothermia is indicated by the degree to which core temperature is lowered: mild hypothermia (34-35 C (93-95 F)); moderate hypothermia (30-34 C (86-93 F)); and severe hypothermia (less than 30 C (86 F)). Hypothermia can also be classified as primary or secondary. Primary hypothermia results directly from an overwhelming cold stress, whereas secondary hypothermia is part of other clinical conditions. Clinical syndromes associated with secondary hypothermia may be acute and severe, such as shock or sepsis.

Signs of hypothermia include poor coordination, stumbling, slurred speech, irrationality and poor judgment, amnesia, hallucinations, blueness or puffiness of the skin, dilation of the pupils, decreased respiratory rate, weak or irregular pulse, and stupor (3). Symptoms of hypothermia include muscle tensing, fatigue, a feeling of deep cold or numbness, intense shivering, poor coordination, stumbling, and disorientation (3). Unfortunately, these signs and symptoms are nonspecific. The only reliable method of diagnosis is measuring core body temperature. Accurate diagnosis is often hindered because thermometers are used that measure body temperature only in the range of 35-42 C (95-104 F). For accurately measuring core body temperature, rectal, rather than oral, temperature should be taken with a low-reading thermometer capable of measuring temperatures from 25 C to 40 C (77 F to 104 F) (4).

The highest mortality rates occur in the elderly. Studies of the regulation of body temperature in the elderly show that physiologic and behavioral components of thermoregulation contribute to an increased vulnerability to hypothermia. Both vasoconstriction and shivering, two primary adaptive physiologic measures to conserve heat, appear to be decreased in some elderly individuals (5-7). Other studies of the behavioral aspects of the response to cold show that, while the elderly prefer temperatures similar to those preferred by the young, a significant number do not discriminate temperatures well, lack precision in adjusting the thermal environment (8), and are less comfortable in cold environments (9).

Gender as a risk factor has been shown in a previous report (10), with males being at greater risk. This could be the result of differences in factors related to physical condition and behavior. Some of these factors include poor physical condition, inadequate nutrition, inadequate insulation/protection or increased exposure to wind, rain, and snow, fatigue, alcohol intoxication, drug overdose, and illness. These factors influence the rate at which the body loses heat when exposed to cold temperatures (4).

Several appropriate prevention goals exist for reducing the risk factors of hypothermia. One goal is to educate the elderly and their health-care providers on the etiology, symptoms, and significance of hypothermia. In implementing this strategy, the elderly who live in poverty and social isolation should be identified and followed. Cases of hypothermia, or situations hastening the onset of hypothermia, could then be more readily recognized and corrected. Another goal is to assure adequate food supply and intake. The production of optimal body heat from metabolic processes will lessen the risk of hypothermia. Finally, assuring adequate space heating is a key preventive measure. For younger persons at risk, activities and travel during cold weather should be attempted only with sufficient clothing and planning, e.g., keeping blankets in the car and the gas tank always at least half full.

References

  1. CDC. Hypothermia--United States. MMWR 1983;32:46-8.

  2. Rango N. Exposure-related hypothermia mortality in the United States, 1970-79. Am J Public Health 1984;74:1159-60.

  3. CDC. Hypothermia fact sheet. Atlanta, Georgia: U.S. Department of Health, Education, and Welfare, Public Health Service, Centers for Disease Control, January 1982.

  4. Collins KJ. Hypothermis: the facts. New York: Oxford University Press, 1983.

  5. Collins KJ, Dore C, Exton-Smith AN, Fox RH, et al. Accidental hypothermia and impaired temperature homoeostasis in the elderly. Br Med J 1977;1:353-6.

  6. Collins KJ, Easton JC, Exton-Smith NA. Shivering thermogenesis and vasomotor responses with convective cooling in the elderly. (Abstract) J Physiol 1981;320:76.

  7. Wagner JA, Robinson S, Marino RP. Age and temperature regulation of humans in neutral and cold environments. J Appl Physiol 1974;37:562-5.

  8. Collins KJ, Exton-Smith AN, Dore C. Urban hypothermia: preferred temperature and thermal perception in old age. Br Med J 1981;282:175-7.

  9. Watts AJ. Hypothermia in the aged: a study of the role of cold-sensitivity. Environ Res 1972;5:119-26.

  10. CDC. Exposure-related hypothermia deaths--District of Columbia, 1972-1982. MMWR 1982;31:669-71.



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