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Environmental heat-related illnesses.

Environmental heat-related deaths and illnesses in the United States are considered preventable (Centers for Disease Control, 1995a). Through education, acclimation, proper hydration, and advanced event planning, hundreds of individuals would not succumb to heat-related illness (Gutierrez, 1995). The spectrum of heat-related illnesses ranges from mild and easily treatable to severe and life-threatening disorders. The purpose of this article is to provide information on environmental heat-related illnesses. This information will include: (a) identifying individuals at risk and contributing factors, (b) signs and symptoms associated with heat-related illness, and (c) current trends in treatment protocol.

Every year the Centers for Disease Control (CDC) creates a Compressed Mortality File (CMF), which contains information compiled from the death certificates recorded in all 50 states and the District of Columbia. From the CMF, there were 5,379 deaths reported during the years of 1979-1992 which were directly attributed to heat illness (CDC, 1995a). According to the most recent statistical data report for 1993, 299 heat-related deaths occurred (Sharon W., National Center of Health Certificates-Mortality Division, personal communication, July 3, 1996).

Heat index and heat wave are two terms used when describing weather conditions. Heat index, refers to an estimation of the influence of temperature (above 90.0 F) and humidity (up to 60%) on the evaporative and radiative transfer of heat between a human and the atmosphere (CDC, 1995b). For example, in Chicago, during the month of July 1995, the heat index rose to 119.0 F. With the intense temperatures, Chicago's Medical Examiner reported 465 heat-related deaths from July 11-27, 1995. In a year that has a documented heat wave (three or more consecutive days of temperatures 90.0 F), such as in 1980, 1,700 individuals died of heat-related causes in the United States.

Deaths due to hyperthermia (individual core body temperature 105.0 F) are underreported because during a heat wave there is an increased mortality of individuals who have a history of cardiovascular and respiratory disease processes (CDC, 1995a). Hyperthermia is reported as a contributing factor to the death of an individual in conjunction with a primary cause (for example, cardiopulmonary failure). Death due to a heat-related cause cannot be documented on the death certificate as the primary cause unless a core body temperature of 105.0 F is taken at or near the time of death.

Individuals at Risk and Contributing Factors

Any individual is at risk to succumb to heat-related illnesses. However, individuals who are at the greatest risk are elderly, children, infants, and individuals that engage in heavy exertion activities such as athletes, military personnel, construction and field workers. Individuals at risk and contributing factors are summarized in Tables 1, 2, and 3.


The elderly are particularly susceptible to heat illnesses because of their inability to acclimatize to the temperature (the ability to adapt to changes in the environment). Other factors that increase the risk for the elderly is the decreased ability to perspire. In addition, the elderly may suffer from chronic systemic conditions, such as cardiopulmonary and cerebrovascular disease (Caroline, 1995). Children and infants are prone to heat illnesses due to their short stature which exposes them to radiated heat from the ground such as asphalt, blacktop, or concrete. Other factors that increase the risk of heat-related illness in infants and children are hypohydration (inadequate hydration during physical activity), obesity, fewer sweat glands that decrease the ability to dissipate heat, and disease processes such as cystic fibrosis and hyperthyroidism (Gutierrez, 1995).

Athletes, military personnel, and laborers (for example, construction workers and field workers) are also at risk for heat illnesses due to body build, exertional activities, and acclimation. Athletes with well-developed muscle mass are at greater risk than athletes with thinner physiques because of the metabolic calories generated during exertion (Birrer, 1988). Individuals who go hiking, biking, camping, and participate in exertional activities sporadically, and those who are in poor physical condition, and have chronic systemic conditions are more prone to heat-related illnesses. Athletes, military personal, and laborers (for example, field workers) must become acclimatized to the hot and humid conditions; this takes at least 10 to 14 days of gradual exposure. During acclimatization, the body increases sweating to lower the elevation of the core temperature. In an unacclimatized individual sweat rates are 1.5 liters per hour but will increase to 2.5 to 3 liters per hour once acclimatized (Kunkel, 1986).

Signs and Symptoms

Varying degrees of signs and symptoms of heat illness may be present depending upon the magnitude of exposure, individual's age, and previous health status. The signs and symptoms extend from mild to life-threatening disorders. A health care practitioner should obtain an accurate history from the individual or others to determine the factors relating to heat illness. The history should include the description and time of onset of the symptoms, exertional activity, past medical history, current medications, and temperature of the environment (Drake & Nettina, 1994).

Minor heat illnesses include heat rash, heat edema, heat tetany, heat syncope, heat cramps, and heat exhaustion (Urbano-Brown & Prouix, 1992). In the majority of these minor heat illnesses, the symptoms are a consequence of the body's defense mechanisms used to dissipate the heat (Tek & Olshaker, 1992). The major and minor heat-related illness signs and symptoms are summarized in Table 4 (Drake & Nettina, 1994).
Table 4. Signs and Symptoms

Condition                Signs and Symptoms

Heat Rash               Rash that is located on the torso,
                         neck, skin folds, and in areas of
                         heavy perspiration.
                        General appearance is a fine, red,
                         papular rash.
Heat Edema              Edema of hand, feet, and ankles.

Heat Tetany             Severe, intermittent tonic contraction
                         of muscles. Usually limited to
                         carpopedal spasms. Normal serum calcium

Heat Syncope            Syncope, hypotension, and orthostatic

Heat Cramps             Intense and painful muscle spasms of
                         the extremities or abdominal muscles.

Heat Exhaustion         Increase fatigue, weakness, anxiety,
                         headache, sweating profusely,
                         irritability, nausea, vomiting, will
                         progress to circulatory
                         collapse with slow and thready
                         pulse, low blood pressure, cold, pale,
                         clammy skin, and mental deterioration.
                         Rectal temperature 104.0 F

Exertional Heat Stroke  Headache, chills, nausea, vomiting,
                         muscle cramps, ataxia, incoherent
                         speech, changes
                         in mental status, may have sweating,
                         tachycardia, hypotension, and a core
                         body temperature
                         of greater than 105.0 F, disseminated
                         intravascular coagulation (DIC),
                         rhabdomyolysis, hyperuricemia, and acute
                         renal failure

Classic Heat Stroke     Headache, chills, nausea, vomiting,
                         ataxia, incoherent speech, changes
                         in mental status, tachycardia,
                         hypotension, seizures,
                         coma, hot and dry skin, and a core
                         body temperature 105.0 F.

Heat rash (miliaria or prickly heat) is a condition of the sweat ducts. The ducts become obstructed and inflamed and the sweat fails to be excreted. This situation causes irritation and itching. The general appearance of heat rash is a fine, red, papular rash that is found predominately on the torso, neck, and skin folds. Heat rash (miliaria) is usually associated with warm and humid weather, but can be seen in individuals who are overdressed.

Heat edema is a condition of swelling of the hands, feet, and ankles. During heat acclimatization women and the elderly are more prone to heat edema. Once acclimatization has occurred the edema is resolved.

Heat tetany is a result of hyperventilation that may develop after heat exposure. Individuals may experience severe, intermittent tonic contractions, and muscle pain. Heat tetany is distinguished from other tetany conditions by the presence of carpopedal spasm and normal serum calcium levels (Cantor, 1991).

Heat syncope is a condition that is associated with prolonged standing and heat exposure. The individual may experience orthostatic dizziness, hypotension, or syncope. In the elderly population heat syncope is due to inadequate vasomotor tone that accompanies the aging adult (Cantor, 1991).

Heat cramps are intense and painful muscle spasms of the extremities or abdominal muscles that have been stressed by strenuous exertion or exercise. Heat cramps take place most often in young and healthy individuals who are sweating profusely while doing strenuous exercises. These young individuals drink water, but fail to replenish the salt that was lost during excessive sweating. Unfortunately, in some individuals excessive or profuse sweating is not detected because of rapid evaporation. An individual who is experiencing heat cramps will have a rectal temperature ranging from 98.6 F to 101.3 F (Yarbrough, 1991).

Heat exhaustion (heat prostration and heat collapse) is considered a minor heat-related condition, unless circulatory failure occurs. This minor heat illness can be divided into two categories: water depletion heat exhaustion and sodium depletion heat exhaustion (Reed & Anderson, 1986). Water depletion heat exhaustion is more common in the elderly population because of inadequate water intake during prolonged exposure to a high heat index. Sodium depletion heat exhaustion occurs in the individual who is not acclimatized to working or exercising in hot and humid climates, has been drinking adequate amounts of fluid, but receiving an inadequate amount of sodium.

The individual will experience a wide range of symptoms with both types of heat exhaustion. Profuse sweating leads to excessive fluid loss, consequently the individual will experience nonspecific symptoms such as increasing fatigue, weakness, anxiety, headache, irritability, nausea, and vomiting. If treatment is delayed, symptoms will progress to circulatory collapse characterized by a slow and thready pulse, low blood pressure, cold, pale, clammy skin, and mental disorientation (Berkow, 1987). Prognosis is good for complete recovery, unless circulatory failure has been prolonged. Differential diagnosis may be difficult in untreated heat exhaustion and heat stroke. Yarbrough (1991) reports that in heat exhaustion the rectal temperature does not exceed 104.0 F, but with heat stroke the rectal temperature is 105.0 F.

Heat stroke (sunstroke and thermic fever) is a major illness that occurs after failure of the body's thermoregulatory system. There are two types of heat stroke: exertional heat stroke -- a condition of increased heat production; and classic heat stroke -- a condition of heat dissipation. Heat stroke is a extremely serious condition resulting in a mortality rate up to 70% or permanent brain damage (Caroline, 1995).

Exertional heat stroke is seen in young healthy individuals, such as athletes or military personnel, who do not have any other predisposing factors. These young healthy individuals have the ability to deal with heat stress on a daily basis, but are overcome by heat generated during increased strenuous exercise in hot and humid climates. Symptoms may progress rapidly and mimic other diseases or conditions, such as prolonged status epilepticus and diabetic ketoacidosis with sepsis. Symptoms include headache, chills, sweating, nausea, vomiting, muscle cramps, ataxia, incoherent speech, core body temperature greater than 105.0 F, tachycardia, hypotension, changes in mental status, or coma (Drake & Nettina, 1994). Other serious potential conditions that may result from exertional heat stroke are disseminated intravascular coagulation (DIC), rhabdomyolysis, hyperuricemia, and acute renal failure due to prolonged elevated core body temperature.

Classic heat stroke (passive heat stroke) generally occurs during heat waves. Individuals most often affected by classic heat stroke are the elderly, very young, and the debilitated. The debilitated are those individuals that have chronic systemic disease processes such as diabetes, impaired sweat production, and cardiopulmonary disease. The symptoms that an individual will experience are similar to exertional heat stroke. The difference between exertional heat stroke and classic heat stroke is that the skin is hot, dry with the absence of sweating, and without muscle cramps. Individuals with classic heat stroke rarely are diagnosed with DIC, rhabdomyolysis, hyperuricemia, and acute renal failure (Reed & Anderson, 1986).

Treatment Protocol

Treatment protocols range from simple treatments that can be accomplished in any setting to complex invasive treatments done in a acute care setting (see Table 5). Heat exhaustion and heat stroke (exertion and classic) require hospitalization.
Table 5. Treatment of Heat Illnesses

Heat Illness                 Treatment
Heat Rash (prickly heat)     Wear nonrestrictive clothing
                             Regular bathing with proper drying
                             Application of talc powder or
                               baking soda to torso, neck,
                               torso, and skin folds
Heat Edema                   Elevation of affected extremity
                               or extremities
                             Support hose during ambulation
Heat Syncope                 Move to a cool shady location
                             Position supine
                             Fluid and salt replacement per
                               mouth or intravenously
Heat Cramps                  Move to a cool shady location
                             Position supine
                             Fluid and salt replacement per
                               mouth or intravenously
                             Exertional activity stopped and
                               avoided for several days
Heat Exhaustion              Move to a cool shady location
                             Position supine
                             Fluid and salt replacement per
                               mouth or intravenously; severe
                               cases--serum electrolytes to be drawn
Heat Stroke - Prehospital    Move to a cool shady location
                             Begin immediate cooling
                             Remove individual's clothing
                             Replace with wet sheets or towels
                             Apply ice to groin, neck, and torso
                             Fluid and salt replacement per
                               mouth or intravenously
                             Start large bore intravenous
                             Transport immediately to a hospital
Heat Stroke - Hospital       Intubation if necessary
                             Begin immediate cooling
                             Remove individual's clothing
                             Replace with wet sheets or towels
                             Apply ice to groin, neck,
                               and torso
                             Consider ice peritoneal ravage
                             Ice bath immersion
                             Cooling blanket
                             Fluid and salt replacement per
                               mouth or intravenously
                               WATCH FOR FLUID OVERLOAD
                             Start large bore intravenous
                             Foley catheter to monitor urine
                               output and diagnostic studies
                             Insert indwelling rectal
                               thermometer for continuous
                               monitoring of temperature
                             Monitor serum laboratory level
                               results treat as indicated:
                               electrolytes, prothrombin time
                               (PT), partial thromboplastin
                               time (PTT), platelet count,
                               fibrinogen levels and fibrin
                               degradation products, liver enzymes
                               including SOOT, blood urea
                               nitrogen and creatine, blood
                               glucose, complete blood count (CBC),
                               and arterial blood gases
                             Electrocardiograph (ECG)
                             Watch for seizure activity

Heat rash (prickly heat) can be treated by removing restrictive and dark-colored clothing. The use of a talc powder or baking soda on torso, neck, and skin folds may help irritation from the rash. Individuals should be instructed about the importance of regular bathing and the proper drying of their skin.

Heat edema is treated by elevating the affected extremity or extremities. The use of support hose during ambulation may prevent venous stasis when there is a decrease in vasomotor tone in the elderly.

Heat syncope and heat cramps are treated similarly. The individual is moved to a cool shady place and positioned supine. Fluid and salt replacement may be accomplished by mouth or through intravenous therapy. An individual who is experiencing either heat syncope or heat cramps will respond after drinking a mixture of 0.5 to 1 teaspoon of salt in a quart of water. If the individual is unable to swallow, then intravenous therapy is instituted and a liter of 0.9% sodium chloride is infused over 1 to 3 hours (Tek & Olshaker, 1992). If heat cramps are a result of exertional activities it is recommended that the activity be stopped immediately and avoided for several days.

An individual who is experiencing heat exhaustion must also be moved to a cool shady environment. Depending on the severity of the symptoms, hospitalization may be required for rehydration and monitoring. If the individual has mild symptoms and tolerates oral fluids, hydration should begin immediately with a salt solution (0.5 to 1 teaspoon of salt in a quart of water). In more severe cases of heat exhaustion, hospitalization is required, so that serum electrolytes may be evaluated. Results of the serum electrolytes will determine if the individual will require a balanced intravenous electrolyte solution. Most individuals will respond to 1 to 2 liters intravenous infusion of 0.9% sodium chloride or a 5% glucose solution in 0.45% sodium chloride over 1 to 3 hours (Tek & Olshaker, 1992).

Heat stroke (exertional and classic), a life-threatening emergency, requires immediate treatment. Heat stroke mortality is directly related to duration of high core body temperature (Reed & Anderson, 1986). Treatment includes immediate cooling by lowering the core body temperature to 102.0 F within 30 to 60 minutes which is required to prevent death or permanent central nervous system damage. Aggressive cooling of the individual prehospital and hospital is necessary. Cooling can be accomplished in the prehospital setting by removing the clothing and replacing the clothing with cold wet sheets or towels to help lower core temperature. Controversy over the benefits of placing ice at the individual's neck, underarms, and groin regions or immersion in an ice bath has arisen. Some practitioners agree that ice placed in strategic locations or ice bath immersion aids in rapidly lowering body core temperature, while other practitioners believe that this treatment produces violent shivering that increases heat production (Yarbrough, 1991). If available, immersion in an ice bath may help lower the individual's temperature, however it is difficult to assess vital signs, perform cardiopulmonary resuscitation, and control seizures (Cantor, 1991).

During treatment of heat stroke, continuous monitoring of the rectal temperature with an indwelling rectal probe is necessary to stop cooling procedures once core body temperature has reached 102.0 F. Central lines are required in heat stroke for the monitoring of central venous pressure and pulmonary wedge pressures. Intravenous fluids of 0.9% sodium chloride or a 5% glucose solution in 0.45% sodium chloride should be administered through large bore catheters for treatment of shock and to aid electrolyte replacement (Tek & Olshaker, 1992). An indwelling Foley catheter is used to test for proteinuria and myoglobinuria. Respiratory status must be monitored carefully for signs of distress and failure, supportive measures may need to be instituted. Individuals who are comatose will require intubation to maintain an airway. Hematologic disturbances may occur especially in exertional heat stroke. If an individual experiences hematologic complications (for example, DIC) this is a sign of deterioration and increases the possibility of mortality.

Prevention and Conclusion

Heat illnesses are a preventable condition. As health care providers, awareness education programs will help prevent heat-related illnesses and may decrease the incidence of heat-related illnesses and morality in the United States. Education is a key component to help individuals learn who and why individuals are at risk for heat-related illnesses. Elderly and children need to keep cool, maintain hydration, and keep in contact with others, so symptoms of heat illness can be detected. Athletes, military personnel, and individuals who participate in strenuous activities should avoid the hottest times of the day, become acclimated, and replenish lost fluids and salts (Birrer, 1988). Learning to dress for hot climates includes wearing light-colored and loose-fitting clothing that will aid in evaporation of perspiration and will reflect some of the sun's rays (Caroline, 1995). Encourage individuals to bring plenty of fluids, such as salt-containing drinks and water, to replenish fluids lost due to evaporation and sweating. Finally, teach the symptoms of early heat illnesses (headache, nausea, cramps, and dizziness) to high-risk individuals, so early treatment can begin. Following these simple preventative measures will decrease the risk for heat-related illnesses.


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Linda L. Davis, MS, RN, ANP, CNOR, is a recent graduate of Arizona State University, Tempe, AZ.
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Author:Davis, Linda L.
Publication:MedSurg Nursing
Date:Jun 1, 1997
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