Problems with Heat & Cold
International travelers encounter environments that may include extremes of climate to which the traveler is not accustomed. Exposure to heat and cold can result in serious injury or death. Travelers should investigate climate extremes that they will face during their journey and prepare with proper clothing, knowledge, and equipment.
Problems Associated with a Hot Climate
Risk for Travelers
Many of the most popular travel destinations are tropical or desert areas. Travelers who sit on the beach or by the pool and do only short walking tours incur minimal risk of heat illness. Those who do strenuous hiking, biking, or work in the heat are at risk, especially travelers coming from cool or temperate climates who are not in good physical condition and are not acclimatized to the heat.
Physiology of Heat Injuries
Tolerance to heat depends largely on physiologic factors, unlike cold environments where adaptive behaviors are more important. The major means of heat dissipation are radiation while at rest and evaporation of sweat during exercise, both of which become minimal with air temperatures above 95°F (35°C) and high humidity.
The major organs involved in temperature regulation are the skin, where sweating and heat exchange take place, and the cardiovascular system, which must increase blood flow to shunt heat from the core to the surface, while meeting the metabolic demands of exercise. Cardiovascular status and conditioning are the major physiologic variables affecting the response to heat stress at all ages. Many chronic illnesses limit tolerance to heat and predispose to heat illness, including cardiovascular disease, extensive skin disorders or scarring that limits sweating, diabetes, and renal disease.
In addition to environmental conditions and intensity of exercise, dehydration is the most important predisposing factor in heat illness. Dehydration also reduces exercise performance, decreases time to exhaustion, and increases internal heat load. Temperature and heart rate increase in direct proportion to the level of dehydration. Sweat is a hypotonic fluid containing sodium and chloride. Sweat rates commonly reach 1 L per hour and may even exceed this level, which results in substantial fluid and sodium loss.
Minor Heat Disorders
Heat cramps are painful muscle contractions following exercise. They begin an hour or more after stopping exercise and most often involve heavily used muscles in the calves, thighs, and abdomen. Rest and passive stretching of the muscle, supplemented by commercial rehydration solutions or water and salt, will rapidly relieve symptoms. Water with a salty snack is sufficient. An oral salt solution can be made by adding one-fourth to one-half teaspoon of table salt (or two 1-g salt tablets) to 1 L of water. To improve taste, add a few teaspoons of sugar and/or orange juice or lemon juice.
Heat syncope is sudden fainting that occurs in unacclimatized people while standing in the heat or after 15–20 minutes of exercise. Consciousness rapidly returns to normal when the patient is supine. Rest, relief from heat, and oral fluids are sufficient treatment.
Heat edema is mild swelling of the hands and feet (more frequent in women) during the first few days of heat exposure. It resolves spontaneously and should not be treated with diuretics, which may delay heat acclimatization and cause dehydration.
Prickly heat (miliaria or heat rash) manifests as small, red, raised itchy bumps on the skin caused by obstruction of the sweat ducts. It resolves spontaneously, aided by avoiding continued sweating and relief from heat. It is best prevented by wearing light, loose clothing and avoiding heavy, continuous sweating.
Major Heat Disorders
Most people who experience acute collapse or other symptoms associated with exercise in the heat are suffering from heat exhaustion—the inability to continue exertion in the heat. The presumed cause of heat exhaustion is loss of fluid and electrolytes, but there are no objective markers to define the syndrome, which is a spectrum ranging from minor complaints to a vague boundary shared with heat stroke. Transient mental changes, such as irritability, confusion, or irrational behavior may be present in heat exhaustion, but major neurologic signs such as seizures or coma indicate heat stroke or hyponatremia. Body temperature may be normal or mildly to moderately elevated.
Most cases can be treated with supine rest in the shade or other cool place and oral water or fluids containing glucose and salt; subsequently, spontaneous cooling occurs, and patients recover within hours. An oral solution for treating heat exhaustion can be made by adding one-fourth to one-half teaspoon of table salt (or two 1-g salt tablets) to 1 L of water plus 4–6 teaspoons of sugar. To further improve taste, add one-quarter cup of orange juice or 2 teaspoons of lemon juice. Commercial sports-electrolyte drinks are also effective. Plain water plus salty snacks may be more palatable and equally effective. Subacute heat exhaustion may develop over several days and is often misdiagnosed as “summer flu” because of findings of weakness, fatigue, headache, dizziness, anorexia, nausea, vomiting, and diarrhea. Treatment is as described for acute heat exhaustion.
Hyponatremia (low sodium [salt] levels in the blood) occurs in both endurance athletes and recreational hikers, likely due to replacement of fluids with excessive amounts of water. The kidneys fail to correct the excess water because of the influence of inappropriate amounts of antidiuretic hormone that act on the kidney to cause retention of water and loss of sodium. Loss of sodium through sweat also contributes to hyponatremia.
In the field setting, altered mental status with normal body temperature and a history of large volumes of water intake suggest hyponatremia. The vague and nonspecific symptoms are the same as those described for hyponatremia in other settings, including anorexia, nausea, emesis, headache, muscle weakness, lethargy, confusion, and seizures. Symptoms of heat exhaustion and early hyponatremia are similar. Hyponatremia can be distinguished from other heat illnesses by persistent alteration of mental status without elevated temperature, delay in onset of major neurologic symptoms (confusion, seizures, or coma), or deterioration up to 24 hours after cessation of exercise and removal from heat. In organized events, measurement of serum sodium should be used to diagnose hyponatremia and guide treatment. Gaining weight or failure to lose weight increases risk of symptomatic hyponatremia.
The recommendation to force fluid intake during prolonged exercise and the attitude that “you can’t drink too much” are major contributors to exercise-associated hyponatremia. Prevention includes drinking only enough to relieve thirst. During prolonged exercise (>12 hours) or heat exposure, supplemental sodium should be taken. Most sports-electrolyte drinks do not contain sufficient amounts of sodium to prevent hyponatremia; on the other hand, salt tablets often cause nausea and vomiting. For hikers, food is the most efficient vehicle for salt replacement. Trail snacks should include not just sweets, but salty foods such as trail mix, crackers, and pretzels.
If hyponatremia is suspected along with neurologic symptoms in the absence of hyperthermia or other diagnoses, restrict fluid. In conscious patients who can tolerate oral intake, salty snacks may be given with sips of water or a solution of concentrated broth (2–4 bouillon cubes in 1/2 cup of water). Obtunded patients may require hypertonic saline.
Heat stroke is an extreme medical emergency requiring aggressive cooling measures and hospitalization for support. Heat stroke is the only form of heat illness in which the mechanisms for thermal homeostasis have failed, and the body does not spontaneously restore the temperature to normal. As a result of uncontrolled fever and circulatory collapse, organ damage can occur in the brain, liver, kidneys, and heart. Damage is related to duration as well as peak elevation of body temperature. The onset of heat stroke may be acute (exertional heat stroke), which can affect healthy people who are exercising in the heat, or gradual (nonexertional heat stroke, also referred to as classic or epidemic), which occurs from passive heat exposure in those with chronic illness.
Early symptoms are similar to those of heat exhaustion, with confusion or change in personality, loss of coordination, dizziness, headache, and nausea that progress to more severe symptoms. A presumptive diagnosis of heat stroke is made in the field when people have elevation of body temperature (hyperpyrexia) and marked alteration of mental status, including delirium, convulsions, and coma. Body temperatures in excess of 106°F (41°C) can occur in heat stroke; even without a thermometer, people will feel hot to the touch. If a thermometer is available, a rectal temperature is the safest and most reliable way to check the temperature of someone who may have heat stroke; an axillary temperature may give a reasonable estimation.
In the field, immediately institute cooling measures by these methods:
- Maintain the airway if victim is unconscious.
- Move to the shade or a cool place out of the sun.
- Use evaporative cooling: remove excess clothing to maximize skin exposure, spray tepid water on the skin, and maintain air movement over the body by fanning. Alternatively, place cool or cold wet towels over the body and fan to promote evaporation.
- Apply ice or cold packs to the neck, axillas, groin, and as much of the body as possible. Vigorously massage the skin to limit constriction of blood vessels and prevent shivering, which will increase body temperature.
- Immerse the person in cool or cold water, such as a nearby pool or natural body of water or bath—an ice bath cools fastest. Always attend and hold the person while in the water.
- Encourage rehydration for those able to take oral fluids.
Heat stroke victims usually have significant dehydration, so intravenous or oral fluid replacement is indicated. Heat stroke is life threatening, and many complications may occur in the first 24–48 hours, including liver or kidney damage and abnormal bleeding. Most victims require hospital intensive care management. If evacuation to a hospital will be delayed, monitor closely for several hours for temperature swings.
Prevention of Heat Disorders
Heat acclimatization is a process of physiologic adaptation to a hot environment that occurs in both residents and visitors. The result of acclimatization is increased sweating with less salt content, and decreased energy expenditure with lower rise in body temperature for a given workload. Only partial adaptation occurs by passive exposure to heat. Full acclimatization, especially cardiovascular response, requires 1–2 hours of exercise in the heat each day. Most acclimatization changes occur within 10 days, provided a suitable amount of daily exercise. After this time, only increased physical fitness will result in further exercise tolerance. Decay of acclimatization occurs within days to weeks if there is no heat exposure.
Physical Conditioning and Acclimatization
Higher levels of physical fitness improve exercise tolerance and capacity in heat, but not as much as acclimatization. If possible, travelers should acclimatize before leaving by exercising ≥1 hour daily in the heat. If this is not possible before departing, limit exercise intensity and duration during the first week of travel in a hot climate. It is a good idea to conform to the local practice in most hot regions and avoid strenuous activity during the hottest part of the day.
Clothing should be lightweight, loose, and light-colored to allow maximum air circulation for evaporation yet give protection from the sun. A wide-brimmed hat markedly reduces radiant heat exposure.
Fluid and Electrolyte Replacement
During exertion, fluid intake improves performance and decreases the likelihood of illness. Reliance on thirst alone is not sufficient to prevent mild dehydration, but forcing a person who is not thirsty to drink water creates the potential danger of hyponatremia. During mild to moderate exertion, electrolyte replacement offers no advantage over plain water. However, for those exercising many hours in heat, salt replacement is recommended. Eating salty snacks or lightly salting mealtime food or fluids is the most efficient way to replace salt losses. Salt tablets, when swallowed whole, may cause gastrointestinal irritation and vomiting but may be better tolerated if 2 tablets are dissolved in 1 L of water. Urine volume and color are a reasonable means to monitor fluid needs.
Problems Associated with A Cold Climate
Risk for Travelers
Travelers do not have to be in an arctic or high-altitude environment to encounter problems with the cold. Humidity, rain, and wind can produce hypothermia even with temperatures around 50°F (10°C). Even in a temperate climate, a traveler in a small boat that overturns in cold water can rapidly become hypothermic. However, reports of severe hypothermia in international travelers are rare. Many high-altitude destinations are not wilderness areas, and villages offer an escape from extreme weather. In Nepal, trekkers almost never experience hypothermia except in the rare instance in which they get lost in a storm.
Hypothermia can be defined as having a core body temperature below 95°F (35°C). When people are faced with an environment in which they cannot keep warm, they first feel chilled, then begin to shiver, and eventually stop shivering as their metabolic reserves are exhausted. Body temperature continues to decrease, depending on the ambient temperatures. As the core temperature falls, neurologic functioning decreases until almost all hypothermic people with a core temperature of 86°F (30°C) or lower are comatose. The record low core body temperature in an adult who survived is 56°F (13°C). Travelers headed to a cold climate should ask questions and research clothing and equipment. Modern clothing, gloves, and particularly footwear have greatly decreased the chances of suffering cold injury in extreme climates. Cold injuries occur more often after accidents, such as avalanches or unexpected nights outside, than during normal recreational activities.
Travelers engaging in recreational activities or working around cold water face a different sort of risk. Immersion hypothermia can render a person unable to swim or keep floating in <15 minutes. In these cases, a personal flotation device is critical, as is knowledge about self-rescue and righting a capsized boat.
The other medical conditions associated with cold affect mainly the skin and the extremities. These can be divided into nonfreezing cold injuries and freezing injuries (frostbite).
Nonfreezing Cold Injury
Nonfreezing cold injuries include trench foot (immersion foot), pernio (chilblains), and cold urticaria. Trench foot is caused by prolonged immersion of the feet in cold water (32°F–59°F; 0°C–15°C). The damage is mainly to nerves and blood vessels, and the result is pain that is aggravated by heat and a dependent position of the limb. Severe cases can take months to resolve. Unlike the treatment for frostbite, immersion foot should not be rapidly rewarmed, which can make the damage much worse.
Pernio are localized, inflammatory lesions that occur mainly on the hands and with exposure to only moderately cold weather. The bluish-red lesions are thought to be caused by prolonged, cold-induced vasoconstriction. As with trench foot, rapid rewarming should be avoided, as it makes the pain worse. Nifedipine may be an effective treatment.
Cold urticaria involves the formation of localized or general wheals and itching. It is not the absolute temperature that induces this form of urticaria but the rate of change of temperature in the skin.
Freezing Cold Injury
Frostbite is the term that is used to describe tissue damage from direct freezing of the skin. Modern equipment and clothing have decreased the risk of frostbite resulting from adventure tourism, and frostbite occurs mainly during an accident, severe unexpected weather, or as a result of poor planning.
Once frostbite has occurred, little can be done to reverse the changes. Therefore, taking great care to prevent frostbite is crucial. Frostbite is usually graded like burns. First-degree frostbite involves reddening of the skin without deeper damage. The prognosis for complete healing is virtually 100%. Second-degree frostbite involves blister formation. Blisters filled with clear fluid have a better prognosis than blood-tinged blisters. Third-degree frostbite represents full-thickness injury to the skin and possibly the underlying tissues. No blister forms, the skin darkens over time and may turn black. If the tissue is completely devascularized, amputation will be necessary.
Frostbitten skin is numb and appears whitish or waxy. The generally accepted method for treating a frozen digit or limb is through rapid rewarming in water heated to 104°F–108°F (40°C–42°C). The frozen area should be completely immersed in the warm water. A thermometer is needed to ensure the water is kept at the correct temperature. Rewarming can be associated with severe pain, so analgesics can be given if needed. Once the area is rewarmed, it must be safeguarded against freezing again. It is better to keep digits frozen a little longer and rapidly rewarm them, than to allow them to thaw out slowly or to thaw and refreeze. A cycle of freeze-thaw-refreeze is devastating to tissue and can lead to amputation.
Once the area has rewarmed, it can be examined. If blisters are present, note whether they extend to the end of the digit. Proximal blisters usually mean that the tissue distal to the blister has suffered full-thickness damage. For treatment, avoid further mechanical trauma to the area and prevent infection. In the field, wash the area thoroughly with a disinfectant such as povidone-iodine, put dressings between the toes or fingers to prevent maceration, use fluffs (expanded gauze sponges) for padding, and cover with a roller gauze bandage. These dressings can safely be left on for up to 3 days at a time. By leaving the dressings on longer, the traveler can preserve what may be limited supplies of bandages. Prophylactic antibiotics are not needed in most situations.
In the rare situation in which a foreign traveler suffers frostbite and can be evacuated to an advanced medical setting within 24–72 hours, there may be a role for thrombolytics, such as prostacyclin and recombinant tissue plasminogen activator. If you are managing frostbite in the first 72 hours, you should consult someone with expertise in frostbite as soon as possible. The risks and benefits of using these drugs should be carefully considered in each patient. Beyond 72 hours after thawing, these interventions are probably not beneficial.
Once the patient has reached a definitive medical setting, there should be no rush to do surgery. The usual time from injury to surgery is 4–5 weeks. Technetium (Tc)-99 scintigraphy and magnetic resonance imaging can be used to help define the extent of the damage. Once the delineation between dead tissue and viable becomes clear, surgery that preserves the remaining digits can be planned.
- Armstrong LE, Casa DJ, Millard-Stafford M, Moran DS, Pyne SW, Roberts WO. American College of Sports Medicine position stand. Exertional heat illness during training and competition. Med Sci Sports Exerc. 2007 Mar;39(3):556–72. [PMID:17473783]
- Bennett BL, Hew-Butler T, Hoffman MD, Roger sIR, Rosner MH, Wilderness Medical Society. Wilderness Medical Society practice guidelines for treatment of exercise-associated hyponatremia: 2014 update. Wilderness Environ Med. 2014 Dec;25(4 Suppl):S30–42. [PMID:25498260]
- Cauchy E, Cheguillaume B, Chetaille E. A controlled trial of a prostacyclin and rt-PA in the treatment of severe frostbite. N Engl J Med. 2011 Jan 13;364(2): 189–90. [PMID:21226604]
- Epstein Y, Moran DS. Extremes of temperature and hydration. In: Keystone JS FD, Kozarsky PE, Connor BA, Nothdurft HD, editor. Travel Medicine. Philadelphia: Saunders Eslevier; 2013. pp. 381–90.
- Freer L, Imray CHE. Frostbite. In: Auerbach PS, editor. Wilderness Medicine. 6th ed. Philadelphia: Mosby Elsevier; 2012. pp. 181–201.
- Hadad E, Rav-Acha M, Heled Y, Epstein Y, Moran DS. Heat stroke: a review of cooling methods. Sports Med. 2004;34(8):501–11. [PMID:15248787]
- Lipman GS, Eifling KP, Ellis MA, Gaudio FG, Otten EM, Grissom CK, et al. Wilderness Medical Society practice guidelines for the prevention and treatment of heat-related illness: 2014 update. Wilderness Environ Med. 2014 Dec;25(4 Suppl):S55–65. [PMID:25498263]
- O’Brien KK, Leon LR, Kenefick RW. Clinical management of heat-related illnesses. In: Auerbach PS, editor. Wilderness Medicine. 6th ed. Philadelphia: Mosby Elsevier; 2012. pp. 232–8.
- Rogers IR, Hew-Butler T. Exercise-associated hyponatremia: overzealous fluid consumption. Wilderness Environ Med. 2009 Summer;20(2):139–43. [PMID:19594207]
Howard D. Backer, David R. Shlim