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Burning Up? A Guide to Treating Heat Illness

Zina Semenovskaya, MD, FAWM; Sage Wiener, MD | June 30, 2017 | Contributor Information

Image from the Bureau of Land Management – Nevada.

In the above image, firefighters simulate the evacuation of a fellow firefighter suffering from heat illness.

Heat illness encompasses a spectrum of disorders caused by environmental heat exposure, including minor conditions—such as heat rash, heat cramps, heat syncope, and heat exhaustion—as well as the most severe condition, heat stroke. Heat stroke is generally defined as a body temperature exceeding 40.5°C (104.9°F) due to environmental heat exposure with lack of thermoregulation, resulting in multiple organ dysfunction or central nervous system abnormalities. [1]

Image from Wikimedia Commons | Nickt.

People at risk for heat-related illness include those who are often exposed to hot climates without sufficient shade, water, or proper clothing. Individuals who are poorly hydrated because of illness, poor fluid intake, or excess alcohol consumption are also at risk. Obesity is an independent risk factor. [2] The chance of developing heat illness is especially high for nonathletes or "weekend warriors" who engage in strenuous physical activities and tend to be less prepared for heat exposure. However, even seasoned athletes may succumb to heat illness, especially with the popularization of extreme sports such as ultramarathons. Compensatory techniques for engaging in hot-weather physical activity include drinking electrolyte-balanced fluid and wearing lightweight, moisture-wicking fabric.

The typical symptoms of heat cramps, heat exhaustion, and heat stroke are shown. Two forms of heat stroke exist [3]: exertional and classic nonexertional. Exertional heat stroke generally occurs in young individuals who engage in strenuous physical activity in a hot environment for a prolonged period. It develops when heat generated by muscular activity builds up faster than the body can release it through cutaneous vasodilation and sweating. [4]

Classic nonexertional heat stroke generally affects sedentary older individuals, people who are chronically ill, and the very young; this type of heat stroke occurs during environmental heat waves. Both types of heat stroke are associated with high morbidity and mortality, especially when therapy is delayed. [3]

Image from the Environmental Protection Agency (EPA).

Between 1979 and 2014, the US heat-related death rate remained for much of the time in the vicinity of about 0.5 deaths per million population (shown), though figures spiked in some years.

Every year an average of 21.5 visits to emergency departments per 100,000 people occur for heat illness. [5] Heat exposure may be responsible for more than 600 deaths in the United States per year, with victims more likely to be male. [6] It is vital to recognize and treat heat illness expeditiously; the sequelae, which can be deadly, include neurologic damage, cardiovascular collapse (eg, prolonged tachycardia in an elderly patient), pulmonary damage, gastrointestinal issues, hepatic failure, renal failure, and rhabdomyolysis. [7]

In the graph, heat was the main cause of those deaths represented by the orange line; the blue line represents deaths only from May to September, with heat being the main or contributing cause of mortality. [8] Because of revisions by the World Health Organization in the international codes used to classify causes of death, it is difficult to compare the pre-1999 mortality rate data with that from or after 1999.

Image from Wikimedia Commons | Sentient Planet.

As shown, heat rash (miliaria rubra) appears as small pinkish pimples and is usually found on body areas covered by clothing.

Heat rash is caused by blockage of the sweat ducts, which results in the leakage of eccrine sweat into the epidermis or dermis. [9] The lesions develop within minutes or hours after the stimulation of sweating and resolve quickly (usually <1 hour after removal of the stimulus that led to sweating). Individuals with heat rash are at particularly high risk for heat exhaustion during exertion in hot weather, because their ability to dissipate heat by means of sweat evaporation is impaired. [10]

Image from Wikimedia Commons | James Heilman, MD.

The image shows myoglobinuria, often described as "Coca-Cola" urine, resulting from rhabdomyolysis, a symptom of heat stroke.

Heat exhaustion may be a precursor of heat stroke; its symptoms include profuse sweating, rapid breathing, and a fast, weak pulse. Symptoms of heat stroke include severely elevated temperature, often greater than 40.5°C (104.9°F); vomiting; hot/dry skin; and tachycardia. In the later stages, central nervous system symptoms such as confusion, ataxia, seizures, and delirium can occur. Other severe symptoms include, as mentioned, rhabdomyolysis, resulting in renal failure and coagulopathy. Heat stroke–related mortality approaches 10%, although in patients presenting with hypotension, it increases to 33%. [11]

Image courtesy of Mark Silverberg, MD.

There are multiple cooling techniques available for the treatment of hyperthermia. [7,10] Evaporative cooling, which is often the most readily available technique, reduces core body temperature in heat stroke by approximately 0.05-0.09 °C (0.09-0.16 °F) per minute. [10] After removing all clothing from the patient, continuously mist him or her with tepid water while directing a large fan at the individual. An alternative (and less time-consuming) evaporative cooling method is to place a wet sheet on the patient (shown).

Strategic ice packing (shown), another simple technique, is often used in conjunction with evaporative cooling, [10] with ice packs placed on the patient's groin, in the axillae, and around the anterior and posterior neck. However, the data to support this cooling strategy are poor, and the other listed cooling methods are significantly more effective at lowering a patient's core temperature. [4]

Image from the Air Force Medical Service.

When available, ice water immersion (demonstrated above), with the patient placed in a large container of ice water, is the treatment of choice for whole-body cooling. [12] Ice water cooling acts faster than evaporative cooling in reducing core temperature, [4] lowering it by approximately 0.15-0.35 °C (0.27-0.63°F) per minute. [10] Ice water immersion should be used with caution in the elderly and in persons with comorbid conditions, due to their higher mortality risk.

Image courtesy of Mark Silverberg, MD.

Whole-body ice packing is similar to ice water immersion and can be used when a large tub is not available. [10] After the patient's clothing has been removed, position the patient on plastic covers or sheets. Ensure that the patient's chest and extremities are covered with crushed ice (shown). A cadaver bag may be used to contain the patient (excluding his/her head) along with the ice and water. The bag is usually readily available in the emergency department, is easy to set up on a stretcher, and is nonporous/leak-proof. This technique maintains room safety by preventing water from spilling onto the floor. The patient and family members should be informed of the purpose of the cadaver bag prior to insertion of the patient.

Another strategy, the use of a cooling blanket, can be employed in conjunction with other techniques to rapidly lower core body temperature. These blankets are made of materials that allow sweating and absorb body heat and are typically filled with cold fluid or gel. After the patient has been completely undressed, the entire body is covered, leaving only the head exposed. While case reports have shown promise for this treatment method, further investigation should be performed before a cooling blanket is used as a first or solitary approach. [13]

Image courtesy of Wikimedia Commons | US Navy, Mass Communication Specialist 1st Class Martine Curaron.

In the above image, a 4-year-old girl undergoes intravenous (IV) treatment for dehydration.

Invasive core cooling can be used in conjunction with external cooling techniques. [10] Cooled intravenous (IV) fluids can be used as a first line of treatment, especially when heat illness is combined with dehydration.

Oral and IV fluid therapy have been shown to be equally effective for hydration in cases of heat illness, but if the patient has altered mental status, IV administration minimizes the risk of aspiration. [4] Administer fluids carefully, because aggressive hydration can result in pulmonary edema. Note that it can be extremely difficult to establish IV access in a dehydrated patient, especially a baby; in these cases, intraosseous access can be used.

Image from Wikimedia Commons | Samir.

As mentioned, complications of IV fluid administration for rapid cooling include pulmonary edema (shown). [10] If providing fluids, administer normal saline or Ringer lactate. Avoid free water, because it can cause hyponatremia and cerebral edema. [10] Patients with altered mental status may benefit from a trial of glucose administration.

Image from Medscape.

More invasive techniques, such as gastric lavage (equipment setup shown), have demonstrated effectiveness in the rapid cooling of patients. The gastric mucosa is a particularly effective surface to cover with cool liquid, because it does not vasoconstrict and can rapidly respond to treatment. [14] Place a large-bore nasogastric or orogastric tube, and connect it to a lavage bag and suction using a Y connector. Rapidly instill 10 mL/kg of ice water over 30-60 seconds, wait approximately 1 minute, and then remove it with suction. Secure the patient's airway to prevent aspiration.

Image from Medscape.

Bladder irrigation can also be used for rapid cooling (setup shown). Although the bladder has a limited surface area, its proximity to the peritoneum and relatively safe access make it a good target for adjunctive treatment. Using sterile technique, place and secure a Foley catheter. Irrigate the bladder with cold normal saline, filling it with 500 mL of fluid; leave the fluid for 1-2 minutes, and then remove it.

Peritoneal lavage is another effective cooling method, because of the peritoneum's large surface area. [14] To perform this procedure, place a standard peritoneal catheter, and lavage with 500-1000 mL of cold fluids. However, while the data for this method have shown significant core temperature reductions in patients, most of the studies were performed in post-cardiac arrest scenarios, using patients with a different physiologic starting point than those experiencing hyperthermia. This must be considered if the clinician is planning to use peritoneal lavage for cooling.

Image from Wikimedia Commons | Anna Frodesiak.

For severe, refractory hyperthermia, even more invasive techniques should be considered if the necessary resources and staffing are available. Methods that have been effective include hemodialysis (shown), cardiopulmonary bypass, and intravascular cooling. [15] Patients with severe hyperthermia may require admission to an intensive care unit for initial cooling and for treatment of subsequent complications, including, potentially, disseminated intravascular coagulopathy.

Image from Wikimedia Commons | James Heilman, MD.

Consider using short-acting benzodiazepines, such as midazolam (shown), to reduce shivering and agitation in patients while instituting rapid cooling. [10] These medications are also useful in treating hyperthermia due to certain drugs and toxins (eg, sympathomimetics). When using benzodiazepines, make sure to carefully monitor the patient's airway and provide symptomatic support. All hyperthermic patients should receive continuous temperature monitoring, ideally with a rectal thermometer; an esophageal probe can also be used, particularly with peritoneal lavage. Cooling techniques should be discontinued once the core temperature reaches 39°C (102.2°F), to prevent rebound hypothermia.

Image courtesy of YouTube | cymcarvalho.

Dantrolene (shown), a muscle relaxant that binds to ryanodine receptors and prevents calcium release, is a highly effective antidote for malignant hyperthermia. [16,17] However, it has not been shown to be effective in treating other types of heat illness. Antipyretics, such as acetaminophen and ibuprofen, are also ineffective at decreasing core body temperature.

Contributor Information

Authors

Zina Semenovskaya, MD, FAWM

Assistant Professor

Department of Emergency Medicine

Mount Sinai St Luke's-Roosevelt Medical Center

New York, NY

Disclosure: Zina Semenovskaya, MD, FAWM, has disclosed no relevant financial relationships.

Sage Wiener, MD

Assistant Professor

Attending Physician, Emergency Medicine

Director, Medical Toxicology

King's County Hospital

State University of New York Downstate Medical Center

Brooklyn, NY

Disclosure: Sage Wiener, MD, has disclosed no relevant financial relationships.

References  

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Image Sources

  1. Slide 1: https://www.flickr.com/photos/blmnevada/27045350763. Accessed June 22, 2017.
  2. Slide 2: https://commons.wikimedia.org/wiki/File:2005_London_Marathon_Lel-Rutto-Gharib.jpg. Accessed June 29, 2017.
  3. Slide 4: https://www.epa.gov/climate-indicators/climate-change-indicators-heat-related-deaths. Accessed June 21, 2017.
  4. Slide 5: https://commons.wikimedia.org/wiki/File:Miliaria_rubra_mild.jpg. Accessed June 29, 2017.
  5. Slide 6: https://commons.wikimedia.org/wiki/File:RhabdoUrine.JPG. Accessed June 22, 2017.
  6. Slide 9: http://www.airforcemedicine.af.mil/MTF/Incirlik/News-Events/Article/623185/59th-mdw-evaluates-improves-heat-illness-procedures/. Accessed June 22, 2017.
  7. Slide 11: https://commons.wikimedia.org/wiki/File:US_Navy_100119-N-7948C-091_Hospital_Corpsman_3rd_Class_Amanda_Vasquez_administers_an_IV_to_a_4-year-old_girl_suffering_from_dehydration_at_a_clinic_at_the_Killick_Haitian_Coast_Guard_Base.jpg. Accessed June 22, 2017.
  8. Slide 12: https://commons.wikimedia.org/wiki/File:AARDS_X-ray_cropped.jpg. Accessed June 29, 2017.
  9. Slide 13: http://emedicine.medscape.com/article/149546-overview. Image gallery: figure 2.
  10. Slide 14: http://emedicine.medscape.com/article/149546-overview. Image gallery: figure 1.
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  13. Slide 17: https://www.youtube.com/watch?v=kSOvl1IzSNY. Accessed June 22, 2017.

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