Medications and Conditions That Potentiate Heatstroke

Heatstroke is a form of hyperthermia that is accompanied by systemic inflammation, causing multiple organ dysfunction and often death.¹ Heatstroke is caused by exposure to a hot and humid environment, but it can be potentiated by the use of certain medications and the pre-existence of certain conditions; persons aged ≥65 years are particularly vulnerable. This column focuses on medications and conditions that can potentiate heatstroke in seniors.

Deaths associated with excessive heat exposure are more common during summer months in which prolonged heat waves have occurred.² In fact, each year, heat waves in the United States claim more lives than the combination of all other weather phenomena, including earthquakes, floods, hurricanes, and tornadoes.3 When vulnerable individuals are exposed to sustained high temperatures, they are susceptible to dehydration and are at particular risk for heatstroke or heat exhaustion. A large number of the deaths attributed to heat exposure occur in persons older than 65 years.² Death rates from other causes, such as cardiovascular disease and respiratory disease, also rise during summer months, particularly during a heat wave.²

Although heatstroke is uncommon in subtropical climates, it often affects individuals who travel to high-temperature climates (eg, pilgrims to Mecca), particularly those who departed from a cold environment.² Nurse practitioners may help reduce morbidity and mortality associated with heatstroke by raising public awareness, recommending measures for prevention, and encouraging prompt intervention by caregivers, spectators, and other healthcare professionals.¹

Pathophysiology and Predisposing Factors

Although heatstroke is attributed to excessive heat exposure, it is defined as a failure to maintain normal body temperature.^4,5 Inadequate or inappropriate response of heat-regulating mechanisms—that is, the body's inability to cope with heat—is often cited as the cause of heat-related morbidity and mortality.⁶

In the elderly, in whom the ability to dissipate heat declines, heatstroke occurs insidiously.⁷ Compared with younger adults, seniors have a reduced sweating response.⁸ Nonexertional (classic) heatstroke, the usual presentation in seniors, is due to both impaired heat loss and failed homeostatic mechanisms; seniors’ susceptibility to this syndrome is related to both physiologic age-related changes and disease.⁸ By contrast, exertional heatstroke is seen in active healthy individuals (eg, athletes, laborers, soldiers) in whom an inability to modulate a sudden massive heat load occurs.¹ The elderly may be less likely than younger individuals to acclimate to heat, contributing to physiologic deficits.⁸ Although risk factors, including some use of certain drugs (Table 1) and pre-existence of certain health conditions,^2,7,9 may predispose some persons to heatstroke, a prolonged heat wave is usually the major precipitating factor.^5,6

Even though heat-related deaths during a heat wave are usually attributed to coronary disease or other cardiovascular disease, primary thermoregulatory failure has a direct relationship to some morbidity and mortality.⁸ Once heatstroke manifests, mortality may be as high as 80%.5 Predisposing factors for heatstroke and for heatstroke-related death are found in Table 2.^2,7,8

Clinical Features

Heatstroke is characterized by a dangerously elevated core temperature of >105º F (>40.6º C), severe central nervous system dysfunction (delirium, psychosis, coma), and anhidrosis (absence of sweating), which causes hot, dry skin.^4,8 Early (prodromal) signs are nonspecific, and include headache, weakness, dizziness, nausea, anorexia, dyspnea, a feeling of warmth, and sometimes vomiting.^4,5,7 Loss of consciousness is typically the first manifestation of heatstroke.⁷

Compared with heatstroke, heat exhaustion (caused by water and electrolyte imbalance) is non–life-threatening; mental status is typically normal and thermoregulation is not impaired.¹ In patients with heat cramps (abrupt exertion-induced contractions, usually of the extremities, occurring during or after exertion), body temperature is normal and other findings are unremarkable.1 Heatstroke is a health emergency that requires hospitalization and continuous monitoring.¹

resuscitation with IV fluids (eg, 0.9% saline solution); supplementation with IV calcium may be necessary for hyperkalemic cardiotoxicity; and alkalinization of urine with IV sodium bicarbonate to potentially help ease nephrotoxicity if myoglobinuria (secondary to rhabdomyolysis) is present; and 

intense management for organ failure and rhabdomyolysis, if present.

Benzodiazepines (eg, lorazepam, diazepam, midazolam) may be used to prevent and/or control agitation, shivering, and seizures, which increase heat production; seizures may occur during the cooling process.^1,2 If benzodiazepines are not effective, barbiturates (eg, phenobarbital) may be used to control seizures.²

Other measures include cooling and IV crystalloid fluids, used initially for hypotension; dobutamine, which is considered for patients who are hypodynamic; and large amounts of IV fluids (up to 10 L may be required), alkalinization of urine (as noted above), and mannitol infusion for the management of rhabdomyolysis.² Of note, antipyretics such as acetaminophen are of no value in the treatment of heatstroke.¹ Also, the muscle relaxant dantrolene, used in the treatment of anesthetic-induced malignant hyperthermia, has not proved beneficial for other causes of severe hyperthermia.¹  

Counseling Patients and Caregivers: Focus on Prevention

The optimal approach to the management of temperature dysregulation in seniors is prevention.⁵ The seriousness of the need for prevention of heatstroke may not be easily understood by patients (Table 4).^2,6,7,10,11 NPs should educate vulnerable patients and caregivers about heatstroke susceptibility, and about the facts that untreated heat exhaustion can progress to heatstroke and that heatstroke can be fatal.¹⁰

If efforts at prevention fail and an elderly person experiences heatstroke, the caregiver must call 911 for assistance and ensure that this person is cooled immediately, as follows:^7,10-12

Gently apply cool water to the skin or use wet compresses to lower body temperature;

Fan the patient; and

Avoid the use of ice packs, which cause shivering and produce heat.

Individuals with heatstroke require specialized treatment and monitoring because of the dangerous nature of the condition.¹⁰ They are best treated in an emergency department and then hospitalized for continued treatment and observation in an intensive care setting.¹⁰

To reiterate the seriousness of the condition and the need for prevention, NPs need to remind patients and their caregivers that, even after a person recovers from heatstroke, his or her body temperature may continue to be abnormal or fluctuate for several weeks.¹⁰ The central nervous system may not fully recover from heatstroke and may result in physical changes (eg, poor coordination) and mental alterations (eg, personality change).¹⁰

Conclusion

A prolonged heat wave is the most likely predisposing factor for heatstroke. Other risk factors include specific medication categories and health conditions. With regard to temperature dysregulation in older adults, prevention appears to be the optimal approach to management. Prevention of serious consequences of heatstroke requires quick recognition and intervention. Complications require intensive multisystem management.

Increased awareness is key to prevention. NPs are encouraged to counsel their patients, including those who travel to countries with warm climates, about the risks involved. NPs may help reduce morbidity and mortality associated with heatstroke by raising public awareness, recommending measures for prevention, and encouraging prompt intervention.