Hyperthermia refers to a group of heat-related conditions characterized by an abnormally high body temperature. It is an abnormally high body temperature caused by a failure of the heat-regulating mechanisms of the body to deal with the heat coming from the environment. Heat fatigue, heat syncope (sudden dizziness after prolonged exposure to the heat), heat cramps, heat exhaustion and heat stroke are commonly known forms of hyperthermia. Risk for these conditions can increase with the combination of outside temperature, general health and individual lifestyle. In humans, core body temperature ranges from 95.9°F to 99.5°F during the day, or 35.5°C to 37.5°C. Hyperthermia is defined as a body temperature greater than 40°C.
Heat Fatigue and cramping
- flushed or red skin
- muscle cramps and/or muscle fasciculation, spasm and pain
- headache or mild light-headedness
- cold, pale, wet skin
- extreme or heavy sweating
- fast but weak pulse
- nausea, vomiting and diarrhea
- muscle cramps
- losing consciousness
People at risk
- Being dehydrated.
- Age-related changes to the skin such as impaired blood circulation and inefficient sweat glands.
- Heart, lung and kidney diseases, as well as any illness that causes general weakness or fever.
- High blood pressure or other conditions that require changes in diet. For example, people on salt-restricted diets may be at increased risk. However, salt pills should not be used without first consulting a doctor.
- Reduced sweating, caused by medications such as diuretics, sedatives, tranquilizers and certain heart and blood pressure drugs.
- Taking several drugs for various conditions. It is important, however, to continue to take prescribed medication and discuss possible problems with a physician.
- Being substantially overweight or underweight.
- Drinking alcoholic beverages.
If you suspect that someone is suffering from a heat-related illness:
- Get the person out of the heat and into a shady, air-conditioned or other cool place. Urge them to lie down.
- If you suspect heat stroke, call 911.
- Encourage the individual to shower, bathe or sponge off with cool water.
- Apply a cold, wet cloth to the wrists, neck, armpits, and/or groin. These are places where blood passes close to the surface of the skin, and the cold cloths can help cool the blood.
- If the person can swallow safely, offer fluids such as water, fruit and vegetable juices, but avoid alcohol and caffeine
Indications for cooling include any signs of heat-related illness in the presence of an elevated body temperature. Previously, heat-related illness has been defined as core body temperature greater than 40 C. However, any elevation above normal body temperature in a symptomatic patient is an indication to consider cooling. The objective is to rapidly decrease the temperature below 40 C, with the final goal of reaching normal range (36 C to 38 C). It is important to note if the patient's other vital signs, like hemodynamic instability, indicate severe heat stroke, in which case, rapid cooling is the most crucial intervention to stabilize the patient.
- Wasserman DD, Healy M. Cooling techniques for hyperthermia.
- Hyperthermia: too hot for your health NIH
- Nye EA, Edler JR, Eberman LE, Games KE. Optimizing cold-water immersion for exercise-induced hyperthermia: an evidence-based paper. Journal of athletic training. 2016 Jun;51(6):500-1.