For much of the country, it has been a pretty warm, if not downright hot, summer. While a chunk of the summer is behind us, many of our states will still be in the path of above-average temperatures and heatwaves. [At the end of this article, download an infographic with heatstroke risk factors, symptoms and factors that can impact body temperature]
Many of us learned about heat exhaustion and heatstroke in our EMT and paramedic classes, but not enough attention was given to non-exertional heatstroke. Also known as classic or urban heatstroke, this form of heat illness is a true emergency, and EMS personnel have a duty to be on the lookout for cases as we are called out for all the other chief complaints that come across the dispatch airwaves. Each year, approximately 658 people die in the United States from heat-related illnesses, and in many cases, the heat emergency goes unrecognized. Unless you are looking for heatstroke, it is easy for the signs and symptoms to be attributed to other illnesses or chronic conditions.
Who is at highest risk for heat-related illness?
Non-exertional heatstroke is most commonly seen in infants, the elderly and individuals who have ongoing or chronic illnesses. It is also often encountered in the homeless population and in low-income areas without air-conditioning.
Noting that it is sometimes called urban heatstroke, cases tend to occur in city environments. Urban housing complexes may have lower rates of air conditioning and the units have less ventilation through the homes. The concrete, asphalt, bricks and other building materials that make up a city environment may also be warmer and retain heat throughout the day and night, making the overall temperature higher than what may be seen in more rural areas. This “urban island heat effect” may even create dangerous conditions for residents in the absence of a declared heatwave.
Pathophysiology of hyperthermia
Our bodies normally produce heat as our cells convert nutrients to energy, and the muscles and tissues use that energy to keep us alive. Each hour, our bodies create 100 kcal of heat, which is enough to raise our body temperature 1.1° C if it is not dissipated. Under the control of the hypothalamus, our body uses mechanisms such as vasodilation, sweating and cardiac output to release the heat and normalize the body temperature.
Many common chronic illnesses and medications can increase heat production and they can also interrupt heat dissipation mechanisms, leading to hyperthermia. Environmental factors may also interfere with heat dissipation. The biggest factor is humidity. Humidity levels above 75% severely limit the evaporation of sweat from a patient’s skin.
Medications that may impact body temperature
- Anticholinergics
- Antidepressants
- Antihistamines
- Beta-blockers
- Diuretics
- Tranquilizers
Illnesses/chronic conditions that may impact body temperature
- Alcoholism
- Diabetes
- Fever
- Hyperthyroidism
- Obesity
- Peripheral vascular disease
- Skin conditions/burn scars
- Sepsis
Travelers beware
Another underappreciated factor in heat emergencies is acclimation to the environment. When a person travels to an area where the ambient temperature is significantly different than what they are used to, it may take 7-10 days for their body to adjust to the new climate. Acclimation is not just a matter of feeling comfortable in a climate; the body’s cooling mechanisms are measurably less effective when a person is not acclimated. A person who is used to a temperature range may be able to secrete two to three liters of cooling sweat per hour, while someone who is not acclimated may only be able to produce one liter per hour. Without the effective cooling mechanism of evaporation, a traveler may be at much higher risk of heatstroke than residents of an area.
Signs and symptoms of heatstroke
The presentation of heatstroke may differ significantly from patient to patient and depend on their health status, the onset of the condition, and the stage in which you find them. Classic signs include hot, flushed skin, fast, weak pulse, tachypnea, an elevated temperature (above 103° F) and an altered level of consciousness. Patients may or may not be sweating.
Treatment and transport for heat-related illness
The treatment priorities for heatstroke include removing the patient from the hot environment and beginning aggressive cooling. The methods you choose will be based on your service protocols and the equipment available to you but may include:
- Ice packs
- Fanning the patient
- Spraying them with water to promote evaporation
- Immersion in an ice bath
- Termination of shivering with benzodiazepines
- Cool IV fluids
Monitor the ABCs and treat any life-threats per your protocols. Transport the patient as soon as possible to a hospital that has an intensive care unit. In-hospital definitive care includes close monitoring of core temperature and other vital signs. End-organ function monitoring, such as urine output and cardiac output, will also be beneficial when available.
Hospital treatments will likely include those started by EMS, plus:
- Cooling blankets
- Gastric, peritoneal, rectal and thoracic lavage
- Cooled oxygen
- Cardiopulmonary bypass
Remain alert for possible cases of non-exertional heatstroke over the next few months, especially if your area is seeing above-average temperatures. Even if the region is not experiencing a true heatwave, keep in mind those patients who are at increased risk of hyperthermia due to their living conditions or health status. Be on the lookout for heatstroke and save a life.
Stay safe out there.
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