Hypothermia is the generalized lowering of body temperature, resulting in a slowing of all physiologic processes, including those of the circulatory, respiratory, and nervous systems. It is caused by any prolonged condition in which body heat loss is greater than metabolic and exertion-related heat production. An annual average of 723 deaths were attributed to hypothermia in the United States between 1979 and 1995.

Hypothermia may be precipitated by accidental cold exposure, immersion, or trauma. In the elderly, hypothermia may develop over hours or days as a result of poor autonomic heat conservation mechanisms, diminished perception of cold, and inadequate environmental heating in the winter. Endocrinologic disorders such as hypothyroidism, hypopituitarism, and hypoadrenalism may result in decreased heat production.

The most significant manifestations of hypothermia are those related to the cardiovascular and central nervous systems. Hypothermia can result in decreased depolarization of cardiac pacemaker cells, reduction in mean arterial pressure and cardiac output, and severe arrhythmias. In addition, metabolism of the central nervous system seems to slow down as core temperature drops.

• Exposure to cold
• Immersion in cold water
• Severe trauma, especially brain injury or burns
• Immobilization
• Age-related autonomic defects in elderly with borderline hypothermia: low peripheral resting blood flow, a nonconstrictive vasomotor response to cold, and easily provoked orthostatic hypotension. A diminished perception of cold and inadequate heat conserving mechanisms in the body contribute to hypothermia in the elderly. Half of all hypothermia-related deaths occur in people over 65.
• Preexisting disease: Heart failure, hypothyroidism, hypopituitarism, hypoadrenalism, uremia, Addison's disease, pulmonary infection, sepsis, ketoacidosis
• Dehydration
• Drugs: Alcohol, tranquilizers, sedatives, hypnotics, antipsychotics
• Poverty, malnutrition, homelessness
• Social isolation or mental illness

• Skin cold to the touch
• Cessation of shivering
• Lethargy, drowsiness
• Weakness, clumsiness
• Irritability, combativeness
• Confusion, delirium, hallucinations
• Depressed reflexes
• Seizure, stupor, or coma
• Slowed, shallow, or arrested respiration
• Slowed, irregular, or arrested heartbeat

• Heart disease
• Diabetic coma
• Hyperinsulinism
• Cerebrovascular accident
• Substance abuse

A core temperature of less than 95 degrees Fahrenheit (35 degrees Celsius) is indicative of hypothermia. Feet, hands, and abdomen are cold to the touch, but shivering is absent except in early cold exposure. Face may be puffy and appear pink or blue. Respirations may be shallow and infrequent. Pulse is slow and patient may be hypotensive.

Blood gases and electrolytes must be monitored carefully, as they may change rapidly during rewarming.

In the hospital setting, core temperature is best monitored using a low-temperature probe in the bladder, rectum, or esophagus.

In some hypothermic patients, an ECG may show a characteristic J wave. In the elderly, the ECG often shows a baseline oscillation produced by rapid fine muscle tremor.

Mild hypothermia is characterized by low body temperature (34 to 35 degrees Celsius, or 93 to 95 degrees Fahrenheit), sluggishness, shivering, confusion, and decreased fine motor coordination. It can be treated by rewarming the conscious patient; simple techniques include the use of blankets, hot water bottles, warm baths, and chemical heat packs placed under the arms and on the chest, neck, and groin. Wet clothing should be removed and replaced with dry, warm clothing and/or blankets.

Severe hypothermia, defined as less than 30 degrees Celsius (86 degrees Fahrenheit) and characterized by very cold skin and an unresponsive state, is a life-threatening emergency. Although respiration and heartbeat may be arrested, the patient should not be considered dead until he or she has been warmed, unless there are other injuries that are obviously not survivable. In the hospital setting or if the hospital is nearby, CPR should be started and sustained, if necessary. A cold heart is prone to ventricular tachycardia or fibrillation. Therefore, a hypothermic patient must be transported very carefully, and there is some controversy as to when or whether to start CPR before reaching the hospital.

At the hospital, fluid and electrolyte balance should be restored using heated IV fluids. Lactated Ringer's is not recommended due to the inability of the hypothermic liver to handle lactate. Elderly patients must be restored to normal temperature slowly (no more than one degree Fahrenheit per hour) or irreversible hypotension is likely. They should be wrapped with blankets in a warm room. Other patients may be immersed in a large tub of water at 113 to 118 degrees Fahrenheit (45 to 48 degrees Celsius) for more rapid warming. All hypothermia victims should be monitored closely.

For profoundly hypothermic patients with cardiac ectopy, a starting dose of bretylium 5 mg/kg IV, repeated at 10 mg/kg as needed, may prevent conversion to ventricular arrhythmia, although there are some conflicting reports of the value of this medication for hypothermia.

Nutritional measures can be quite helpful in preventing the development of hypothermia. Animal studies suggest that Western and Chinese herbal therapies influence body temperature and, therefore, may translate into a possible protective benefit for prevention of hypothermia if used prior to, or just following, cold exposure. Depending on results from future scientific studies, they may also be a useful treatment once hypothermia has set in. Vasodilating herbal and supplemental substances may compound the adverse effects of hypothermia and must be avoided. Similarly, specific acupuncture points may induce hypothermia.

While not proven in clinical trials, consumption of sufficient caloric intake of proteins and fats before and during exposure to cold weather conditions is advisable, particularly for the elderly. Patients in such situations may be advised to carry high—calorie snacks such as protein bars and nuts and to not wait until hunger develops in order to eat. Regular intake of fluids - water, juices, and electrolyte replacement drinks—prevents dehydration; similar to food, patients at risk should be advised not to wait for thirst in order to drink fluids (Semenza et al. 1995; Worfolk 2000). Alcohol and caffeine should be avoided because of their vasodilating effects, which allows blood to be shunted to the periphery, promoting cooling of the central core.

An Indian composite herbal preparation (CIHP-I) containing Withania somnifera, Asparagus racemosus, Pueraria tuberosa, Mucuna pruriens, Dioscorea bulbifera, Argyria speciosa, Piper longum, and asphalt has been evaluated for its properties as an adaptogen. (Asphalt, a mixture of fresh and modified remnants of humus mixed with plant and microbial metabolites, is found at moderately high altitudes throughout the world.) Rat studies demonstrated a beneficial cumulative effect of increased thermoregulation capacity under extreme conditions in CIHP-I-treated rats. After exposing rats to low temperatures and atmospheric pressure and inducing hypothermia, CIHP-I was found to mobilize free fatty acids for extra energy generation and to spare carbohydrate reserves, evidenced by better-maintained blood glucose and muscle glycogen levels in the CIHP-I treatment group (Kumar et al. 1999). (Note: Although individual herbs are available in health food stores, it is advisable to obtain combinations of herbs from a trained Ayurvedic practitioner.)

Although this herbal composite needs to be studied in a human population, these early results raise questions about whether this combination may prove to be of value as a preventive agent either prior to, or following, cold exposure, or as a treatment in the early phases of hypothermia.

Although it has not been studied in relation to hypothermia treatment specifically, ginseng (Eleutherococcus senticosus and Panax ginseng) is also traditionally known as an adaptogen (a substance that helps to rebuild strength and regenerate the body after stress or fatigue), according to Murray and Pizzorno (1999) and is used to enhance resistance to adverse conditions such as hypothermia (Blumenthal et al. 2000). This may be of benefit as a preventive measure in people who are regularly subjected to extreme weather conditions, in elderly populations, and in those with debility and chronic disease.

The Chinese herbal medicine, Danggui-sini-jia-wuzhuyu-shengjiang-tang [Toki-shigyakuka-gosyuyu-syokyo-to (TSGS-to) in Japanese], was evaluated for its ability to elevate temperature by increasing peripheral circulation. The formulas contain Angelicae radix, Cinnamomi cortex, Evodiae fructus, Glycyrrhizae radix, Zingiberis rhizoma, Akebiae caulis, Zizyphi fructus, Asiasari radix, and Paeoniae radix. Thermographic studies were performed on rats receiving a single oral dose of TSGS-to compared to a control group receiving only boiled water. TSGS-to administration significantly elevated the calories of heat radiating from rat tails 10 minutes after uptake; the increase in temperature remained constant for more than 20 minutes, only decreasing 60 minutes after uptake and returning to baseline after 90 minutes. The untreated group had a transient temperature elevation 5 minutes after water uptake with a return to baseline 10 minutes later. Upon concluding, the researchers raise the possibility that TSGS-to may ultimately prove useful for patients with autonomic disorders who, despite warm conditions and improvement in core temperature with treatment for hypothermia, continue to complain of cold extremities (Kanai et al. 1997).

Certain herbs used in Traditional Chinese Medicine (TCM) may induce hypothermia. Rats administered Clerodenron fragrans (Ventenaceae), for instance, became hypothermic in moderate and cold temperatures because of decreased metabolic heat production. In warm temperatures, there was no thermoregulatory effect (Lin et al. 1981). In addition, TCM remedies used to treat fever, such as Huang chin (Scutellaria baicalensis George) may induce hypothermia as demonstrated in rat studies (Lin et al. 1980).

Homeopathic remedies have been used clinically in first aid and other acute situations; however, the specific value for hypothermia remains to be explored in scientific studies.

Caution must be exercised when using acupuncture to treat fever. Needle stimulation of acupuncture points, chu-chih (LI-11) and ho-ku (LI-4), has been found to produce hypothermia in 18 normal adults as a result of decreases in metabolic heat production and cutaneous vasodilation (Lin et al. 1981).

Massage is contraindicated until core temperature has normalized because of the potential risk of peripheral vasodilatation and circulatory collapse.

Hypothermia can generally be prevented by preparing appropriately for environmental conditions, coupled with early recognition of symptoms of exposure and prompt medical attention. In cold weather, people who plan to be outdoors for extended periods should wear insulated or layered moisture-wicking clothing, including headgear. They should avoid overexertion, maintain adequate food and fluid intake, and abstain from alcohol (see section entitled Nutrition for more details). Hypothermia-prone populations such as elderly or homeless people should be referred to social service agencies, if necessary, for assistance in maintaining adequate housing, heat, and clothing. The elderly should be routinely monitored for low body temperature.

• Hypoxia
• Tissue necrosis
• Gangrene of the extremities
• Pancreatitis
• Pulmonary edema
• Pneumonia
• Metabolic acidosis
• Renal failure
• Ventricular fibrillation and other arrhythmias

Patients with mild hypothermia have an excellent prognosis; this form of the condition is not associated with significant morbidity or mortality. However, even moderate hypothermia (characterized by delirium, slowed reflexes, and a body temperature of 86 to 93.2 degrees Fahrenheit (or 30 to 34 degrees Celsius)) presents a 21% mortality rate. Children are more likely to recover from severe hypothermia than adults. The overall mortality rate for accidental hypothermia in the elderly is about 50%, with survival largely determined by how soon the temperature fall is interrupted, and the presence and severity of complications.

Hypothermia victims have recovered without permanent brain damage from immersion in icy water for up to 1 hour, and in rare cases even longer, with core temperatures as low as 79 degrees Fahrenheit (26 degrees Celsius). In small children, hypothermia from immersion in cold water may protect the brain from hypoxia in near-drownings.

Beers MH, Berkow R, eds. The Merck Manual of Diagnosis and Therapy. Whitehouse Station, NJ: Merck & Co. 1999:2451-2452, 2507-2508.

Blumenthal M, ed. The Complete German Commission E Monographs: Therapeutic Guide to Herbal Medicines. Boston, Mass: Integrative Medicine Communications; 1998:138-139, 142-143, 148-149, 197.

Blumenthal M, Goldberg A, Brinckmann J, eds. Herbal Medicine: Expanded Commission E Monographs. Newton, Mass: Integrative Medicine Communications; 2000:106-109, 170-177.

Centers for Disease Control and Prevention. Hypothermia-related deaths: Georgia, January 1996–December 1997, and United States, 1979–1995. MMWR Morb Mortal Wkly Rep. 1998;47:1037-1040.

Decker W. Hypothermia. In: Adler J, et al. eds. Emergency Medicine: An On-line Medical Reference. Accessed at www.emedicine.com on January 19, 2000.

Hayward JS, Eckerson JD, Kemna D. Thermal and cardiovascular changes during three methods of resuscitation from mild hypothermia. Resuscitation. 1984;11:21-33.

Kanai S, Okano H, Abe H. Efficacy of Toki-shigyakuka-gosyuyu-syokyo-to (Danggui-sini-jia-wuzhuyu-shengjiang-tang) on peripheral circulation in autonomic disorders. Am J Chin Med. 1997;25(1):69-78.

Kumar R, Grover SK, Shyam R, Divekar HM, Gupta AK, Srivastava KK. Enhanced thermogenesis in rats by a composite Indian herbal preparation-I and its mechanism of action. J Altern Complement Med. 1999;5(3):245-251.

Lin MT, Chandra A, Chen-Yen SM, Chern YF. Needle stimulation of acupuncture loci chu-chih (LI-11) and ho-ku (LI-4) induces hypothermia effects and analgesia in normal adults. Am J Chin Med. 1981;9(1):74-83.

Lin MT, Ho ML, Chandra A, Hsu HK. Serotoninergic mechanisms of the hypothermia induced by Clerodenron fragrans (Ventenaceae) in the rat. Am J Chin Med. 1981;9(2):144-154.

Lin MT, Liu GG, Wu WL, Chern YF. Effects of Chinese herb, Huang chin (Scutellaria baicalensis George) on thermoregulation in rats. Jpn J Pharmacol. 1980;30(1):59-64.

Murray JE, Pizzorno MT, eds. Textbook of Natural Medicine. Edinburgh: Churchill Livingstone; 1999: 531.

Weinberg AD. Hypothermia. Ann Emerg Med. 1993;22 (Pt 2):370-377.

Semenza JC, McCullough JE, Flanders WD, McGeehin MA, Lumpkin JR. Excess hospital admissions during the July 1995 heat wave in Chicago. Am J Prev Med 1999;16(4):269-277.

Worfolk JB. Heat waves: their impact on the health of elders. Geriatric Nursing: American Journal of Care for the Aging. 2000;21(2):70-77.