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Summary of Wilderness Medical Society Clinical Practice Guidelines for the Prevention and Treatment of Heat Illness: 2019 Update

Article Date:  January 29, 2020

To provide guidance to clinicians and disseminate knowledge about best practices, the Wilderness Medical Society (WMS) convened an expert panel to develop evidence-based guidelines for prevention and treatment of heat illness. Preventive and therapeutic modalities are presented, and recommendations made for each form of heat illness.

The term “heat illness” refers to a family of disorders that are often encountered together in hot environments, or in other situations that cause heat to accumulate in the body. Defining these conditions can be difficult due to the overlap of different phenomena that may contribute to edema or syncope in hot environments. When approaching patients in hot environments, keep in mind two important distinctions. First, hyperthermia refers to an elevation in the body’s core temperature, distinct from heat illness. Hyperthermia can be a normal physiologic response, with athletes’ core temperatures regularly rising to 39°C (103°F) during exertion while the athlete maintains excellent overall physical and mental function. Heat illness occurs when the core temperature is elevated and compromises homeostasis. Second, the distinction between heat exhaustion and heat stroke is critical. Heat exhaustion is characterized by thirst, weakness, and malaise with a core temperature typically below 40°C (104°F). Heat stroke is defined by central nervous system symptoms such as confusion, seizure, or coma at a core temperature above 40°C (104°F) in a setting that suggests the high temperature itself is contributing to the symptoms; in the absence of a clear alternate cause for CNS symptoms such as head trauma, intoxication, hyponatremia, or sepsis, a temperature over 40°C (104°F) can be considered an etiology for that altered mental status, therefore the core temperature itself should be considered a target of therapy.

The guideline reviews evidence for different techniques used to prevent heat illness. Risk factors for any individual include certain medications, gear choices, and hydration status. Of these, usually hydration status is the most modifiable once in a hot environment. We recommend a drink-to-thirst approach to stay in the sweet spot: not so dry as to overheat, but not so overhydrated as to exacerbate exercise-associated hyponatremia. The environmental risk is best assessed through the use of the wet-globe bulb temperature index, a composite measure that considers temperature, humidity, and direct solar radiation. When designing an activity, think of ways to dissipate heat during breaks. When choosing gear, consider how to optimize evaporation, convection, conduction, and radiation to your advantage.

Heat illness treatment algorithm.

The guideline also reviews evidence for different techniques for treating heat illness, mostly focused around which ones can most rapidly and safely drop the core temperature. Field treatment teams should focus first on the basic resuscitation principles of stabilizing the airway, breathing, and circulation, then focus on measuring, then lowering the patient’s temperature. When concerned about core temperature, measure it like you mean it: rectally if at all possible.

Passive cooling techniques limit heat exposure and promote natural heat loss—getting the patient into a cooler environment and isolated from hot surfaces like pavement. These are important steps for everyone’s safety but have relatively little evidence to prove their efficacy.

Active cooling techniques remove heat from the body by direct interventions. These are best done after removing all equipment and loosening clothing. Cold water immersion is the fastest method to drop the core temperature. A slurry of water and ice can also be wrapped against the patient in a tarp if an immersion bath is not practical. If using immersion in a body of water, protecting the airway against aspiration is of paramount importance. If cold-water immersion is not available, then evaporative cooling with misting and fanning is the next best thing, about half as effective as immersion, when it is done with a good breeze and maximized skin exposure. If using chemical cold packs, put them on the face, palms, and soles instead of the neck, groin, or armpits. Antipyretic drugs such as aspirin or acetaminophen do not help—save them for the headache your team will have after transferring the patient to a hospital.

If practicing in a hospital setting, consider establishing protocols to use conductive cooling with cold-water immersion. This approach is the most effective, but may be impractical in the elderly critically ill patient. Your team may love it though, for treating multiple patients arriving from a high-risk event such as a hot-weather road marathon. Just imagine it—a dozen icy tarp tacos with coolers of ice in the ambulance bay sounds much nicer than twelve crazed, combative athletes in the main ED who need to be sedated, intubated, then have cooling lines placed—everyone on the team, from the chief medical officer to your inventory staff, hates the second plan. Let’s all give peace, and ice, a chance.


Lipman GS, Gaudio FG, Eifling KP, Ellis MA, Otten EM, Grissom, CK. Wilderness Medical Society clinical practice guidelines for the prevention and treatment of heat illness: 2019 update. Wilderness Environ Med. 30(4S):S33–46.

Published January 29, 2020

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