Howard D. Backer, David R. Shlim

Background

Foreign travel involves heading into new environments, and climate is one of the most important factors to consider. Travelers may encounter temperature and weather extremes that are either much hotter or colder than they are used to, and either extreme can have health consequences.

Travelers should try to determine the likely climate extremes that they will face during their journey and to prepare with proper clothing, knowledge, and equipment. This section gives a brief overview of the topic.

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 or biking in the heat may have significant risk, especially travelers coming from cool or temperate climates who are not in good physical condition and unacclimatized to the heat.

Clinical Presentations

Physiology of Heat Injuries

Tolerance to heat depends primarily on physiologic factors, unlike cold environments where adaptive behaviors are more important. The major means of heat dissipation are radiation 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 greatly 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. Dehydration is the most important predisposing factor in heat illness; 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 1–2 L/hr, which may result in significant fluid and sodium loss.

Minor Heat Disorders

Heat cramps are painful muscle contractions following exercise in heat. They begin an hour or more after stopping exercise, most often involving heavily used muscles in the calves, thighs, and abdomen. If rest and passive stretching of the muscle do not resolve cramps, an oral salt solution, as in rehydration solutions, will rapidly relieve symptoms.

Heat syncope is sudden fainting in heat that occurs in unacclimatized people while standing 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 treatments.

Heat edema is mild swelling of the hands and feet, which is 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 acclimatization and cause dehydration.

Prickly heat (e.g., miliaria, heat rash) manifests as small, red, pruritic lesions on the skin caused by obstruction of the sweat ducts. It is best prevented by wearing light, loose clothing and avoiding heavy, continuous sweating.

Major Heat Disorders

Heat Exhaustion

• Most people who experience acute collapse or other symptoms associated with exercise in the heat are suffering from heat exhaustion, simply defined as 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, but neurologic signs, such as seizures or coma, would indicate heat stroke or hyponatremia.
• Body temperature may be normal or elevated.
• Most cases can be treated with supine rest in a cool place and oral water or fluids containing glucose and salt. Spontaneous cooling occurs, and patients recover within hours, preventing progression to more serious illness. An oral solution for treating minor heat disorders or for fluid and electrolyte replacement can be made by adding ¼ teaspoon or two l-gm salt tablets to l liter of water, plus 4–8 tsp of sugar if desired for taste.
• 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.

Exercise-Induced Hyponatremia

• Some travelers are so concerned about preventing heat illness and dehydration that they adopt the attitude that “you can’t drink too much.” Sadly, this attitude can lead to tragic outcomes.
• Hyponatremia due to excessive water intake occurs in both endurance athletes and recreational hikers, particularly if the person is replacing sodium loss through sweating with plain water.
• In the field setting, altered mental status with normal body temperature and a history of large volumes of water intake are highly suggestive of hyponatremia. The vague and nonspecific symptoms are the same as those described for hyponatremia in other settings (e.g., anorexia, nausea, emesis, headache, muscle weakness, lethargy, confusion, and seizures).
• Until clinically apparent alterations in mental status appear, heat exhaustion is difficult to distinguish from early hyponatremia.
• A delay before onset of major symptoms or deterioration after cessation of exercise and heat exposure are unique aspects of hyponatremia.
• Prevention includes sodium supplementation with prolonged exercise or heat exposure. For hikers and wilderness users, food is the most efficient vehicle for salt replacement. Trail snacks should include salty foods (e.g., trail mix, crackers, pretzels, jerky), and not just sweets.

Heat Stroke

• 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. As a result of uncontrolled fever and circulatory collapse, organ damage can occur in the brain, liver, kidneys, and heart.
• The onset of heat stroke may be acute (exertional heat stroke) or gradual (nonexertional heat stroke, also referred to as classic or epidemic).
• A presumptive diagnosis of heatstroke is made when patients have hyperpyrexia and marked alteration of mental status.
• Body temperatures in excess of 106° F (41° C) can be observed; even without a thermometer, these patients will feel hot to touch. If a thermometer is available, a rectal temperature is the safest and most reliable way to check the temperature in someone who may have heatstroke.
• In the field, institute evaporative cooling by maximizing skin exposure, spraying tepid water on the skin, and maintaining air movement over the body by fans. If ice is available, apply cold packs to the neck, axillas, and groin and massage the skin with ice. Immersion in a nearby pool or natural body of water can initiate cooling.
• Unless the recovery is very rapid, the person should be evacuated to a hospital. If that is not possible, encourage rehydration, if the person is able to take oral fluids, and monitor closely for several hours.

Prevention of Heat Disorders

Heat Acclimatization

Heat acclimatization is a process of physiologic adaptation to a hot environment that occurs in both residents and visitors. The result of acclimatization is an increase in sweating, 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 exercise is taken each day in the heat. 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 at least 1 hour daily in the heat. If this is not possible before departing, exercise in heat during the first week of travel should be limited in intensity and duration (30- to 90-minute periods) with rest in between. 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

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 significant dehydration. During mild to moderate exertion, electrolyte replacement offers no advantage over plain water. However, for those exercising many hours in heat, a weak solution similar to commercial electrolyte drinks is recommended. Salty snacks or light salting of 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 two tablets can be dissolved in one liter of water. Urine volume and color are a readily available 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 (12° C–14° C). 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 may get lost in a storm. Even in a temperate climate, the traveler in a small boat that overturns in very cold water can rapidly become hypothermic.

Clinical Presentations

Hypothermia

Hypothermia can be defined, in general terms, as having a core body temperature of <95° F (35° C). When persons 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. At that point, body temperature continues to decrease, dependent upon 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) 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 be encouraged to ask questions and research appropriate clothing and equipment.

Travelers who will be recreating or working around cold water face a different sort of risk. Immersion hypothermia can render a person unable to swim or keep floating within 30–60 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

The nonfreezing cold injuries are—

• Trench foot (immersion foot): This condition 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 (chilblains): Pernio are localized, inflammatory lesions that occur mainly on the hands of susceptible individuals. They can occur 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: This condition involves the formation of localized or general wheals and itching after exposure to cold. It is not the absolute temperature that induces this form of urticara, but the rate of change of temperature in the skin.

Freezing Cold Injury

Categories of Frostbite

• Frostbite is the term that is used to describe tissue damage from direct freezing of the skin.
• Modern equipment and clothing have greatly decreased the risk of frostbite in most adventurous tourist destinations, and frostbite occurs mainly during an accident, severe unexpected weather, or as a result of poor planning.
• Once frostbite injury 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, and if the tissue is completely devascularized, amputation will be necessary.

Management of Frostbite

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 maintain the water at the correct temperature. Rewarming can be associated with severe pain, and analgesics can be given if needed. Once the area is rewarmed, it must be safeguarded against freezing again. It is thought to be 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 leads more directly to the need for amputation.

Once the area has rewarmed, it can be examined. If blisters are present, it is important to 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. Treatment consists of avoiding further mechanical trauma to the area and preventing infection. Reasonable field treatment consists of washing the area thoroughly with a disinfectant such as povidone–iodine, putting dressings between the toes or fingers to prevent maceration, using fluffs (expanded gauze sponges) for padding, and covering 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.

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. By that time the dead tissue has begun to separate from viable tissue, and the surgeon can plan surgery that maximizes the remaining digits.

References

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5. McCauley RL, Killyon GW, Smith DJ Jr, et al. Frostbite. In: Auerbach PS, editor. Wilderness medicine. 5th ed. Philadelphia: Mosby; 2007.