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Hyperthermia: EMS assessment and management

Learn the pathophysiology of heat-related illness, recognition of heat emergencies and treatment principles


High ambient temperatures increase the risk of heat stroke and heat exhaustion.


Article updated October 1, 2018

It’s the fifth day of an oppressive heat wave that has blanketed the region. With temperatures in the low 100s F and humidity above 90 percent, radio announcers urge people to remain out of the heat. Nevertheless, there are a growing number of heat-related illness patients being seen at the emergency departments in the area.

Your unit is toned out for an “elderly female unconscious” at a home on the outskirts of town. When you arrive, you are met by a young man who had come by to check on his grandmother. She had not been heard from since the heat wave began and her family became concerned.

The house is oppressively hot as you enter. Other rescue members open windows and doors as you begin your assessment of an older woman lying on the floor. You note that there is an overturned walker lying near her. She is unresponsive to painful stimulus and is incontinent of urine and feces. Her skin is pale and quite hot to the touch.

Introduction to hyperthermia

Hyperthermia is a world-wide problem that is likely to increase as the global environment continues to warm. While the ambient environment may be the major factor in an increasing number of temperature-related illnesses, other causes of hyperthermia may be more difficult to detect. EMS providers must be able to identify and quickly manage the effects of hyperthermia in patients, as they may be life-threatening.

Scope of the problem

Millions of people across the globe are exposed to extreme temperatures regularly. In 1995, a heat wave in Chicago resulted in over 700 deaths, mostly related to heat-related illness [1]. A European heat wave in 2003 resulted in over 70,000 deaths [2]. A 2015 heat wave killed over 1,400 people in India and in Pakistan heat resulted in over 2,000 deaths [3].

A study conducted by the U.S. Army showed that, while the number of hospitalizations from heat-related illnesses had dropped from 1980 to 2002, the rate of the most serious hyperthermic condition, heat stroke, actually increased five-fold. Dehydration, rhabdomyolysis and acute renal failure were often involved in these cases [4].

Not all cases of hyperthermia are related to environmental temperature. Malignant Hyperthermia is a rare but life-threatening condition, stemming from a reaction to certain medications such as succinylcholine and certain anesthetic medications. Up to 700 cases are suspected to occur in the U.S. annually [5].

Maintaining core body temperature

The human body continually works to keep things in balance. Maintaining an even core body temperature is a major component of homeostasis; all of the critical bodily functions operate most efficiently at normal body temperature, which ranges from 36.5 to 37.5 C (97.7-99.5 F). Core temperature will vary by a half to one degree throughout the day, with the body being cooler while sleeping and warmest by later afternoon. The body generates most of its heat from metabolic processes in deep organs such as the liver, heart and brain, as well through small musculoskeletal contractions.

Setpoint is the body’s attempt to maintain a normal operating temperature. The setpoint is controlled by the hypothalamus, which receives signals from receptors in the skin and bloodstream. When the body is under attack from a virus or bacteria, part of the immune response will cause the temperature setpoint to rise, resulting in a fever that helps to combat the infectious agent.

During a fever (pyrexia) the body will implement several mechanisms to allow excess heat to dissipate more readily. Vasodilation occurs, causing skin to flush and bring more blood to the surface. Sweat glands secrete fluid, causing evaporation to occur at the skin’s surface and increasing the efficiency of heat loss. These are the signs seen when evaluating patients with an infection.

When the fire gets out of control

Hyperthermia occurs when the body’s core temperature rises above the normal range, but without a change in setpoint. This occurs when normal cooling mechanisms are unable to compensate for the increasing temperature inside the body. It may be the result of excessive external temperature, a rapid buildup of internal temperature, or a loss of control by the hypothalamus.

An excessive heat environment is the most common cause of hyperthermia. As the body absorbs heat it will respond normally through vasodilation and diaphoresis. As water is lost, electrolytes such as sodium are either concentrated or displaced. A person may experience localized reactions such as heat cramps in large muscle groups such as in the leg or abdomen.

A loss of 5-6 percent water loss will cause the signs of heat exhaustion:

  • Weakness
  • Nausea
  • Headache
  • Exhaustion

However, internal body temperature remains relatively normal.

If the victim remains in the excessive heat environment, compensatory mechanisms fail and body temperature rises dramatically. Heat stroke signs and symptoms are when the body temperature rises above 41.1 C (106 F) and there is change in the patient’s mental status [6].

Heat stroke is divided into two types:

  1. Exertional heat stroke results from excessive physical exertion in a hot environment, as might befall a marathon runner or football player.
  2. Nonexertional heat stroke affects those who have difficulty leaving an overheated environment, such as elderly or young pediatric patients.

As the body overheats, proteins begin to unravel (denature) and basic metabolic processes falter and eventually stop. Cell membranes rupture, causing major inflammation throughout body tissues that can lead to systemic inflammatory response syndrome (SIRS) and multi organ dysfunction syndrome (MODS).

There are other causes of hyperthermia. Certain recreational drugs such as lysergic acid diethylamide (LSD) and cocaine can cause body temperature to rise dramatically at toxic levels. In the operating theater, the administration of succinylcholine or volatile inhalational anesthetic can cause an abnormal release of calcium into cells, causing a rapid burst of muscular activity which is called malignant hyperthermia. This results in acidosis, hypercarbia, hyperkalemia and hyperthermia.

Other causes of hyperthermia include neuroleptic malignant syndrome, an adverse reaction to certain antipsychotic drugs such as first generation (e.g. phenothiazines) and second generation (e.g. resperidone and olanzapine).

Heat stroke treatment

In mild cases of hyperthermia, treatment is supportive. Removing the patient from a heated environment is the first intervention, followed by passive cooling measures such as removing clothing and fanning air across the skin. Depending upon local protocols, hydration orally or intravenously can help restore water balance quickly.

In more severe cases of heat stroke, active cooling measures are required to bring the body temperature down more quickly. After removing the patient’s clothing, misting their body with water will increase heat loss through evaporation. Packing the groin and axilla (armpits) with ice or icepacks, along with evaporative cooling can reduce body temperature by 0.02-0.03 C per minute [7].

Monitor the patient’s body temperature with a thermometer during cooling and transport. If the patient is unresponsive use a rectal thermometer.

Theoretically we want to avoid overshoot, causing potential hypothermia and unwanted shivering, which generates heat. But most patients will have short duration on-scene and transport times and though rapid and agressive, lowering a patient’s core temperature with active cooling measures is still time consuming.

In hospital cooling measures may include gastric or peritoneal lavage, where chilled saline fluid is introduced into the gut or abdominal cavity. Antipyretics such as acetaminophen or ibuprofen are not effective for reducing hyperthermia. Benzodiazepines may be administered to reduce agitation and muscle tremors that result from the cooling measures.

Heat exhaustion treatment

For patients who have signs and symptoms of hypovolemic shock, volume replacement is indicated. A crystalloid solution such as lactated ringers or normal saline can be infused quickly. Large amounts of saline should be avoided however, since sodium levels may be already high.

Case study follow-up

After establishing airway and breathing control, your physical exam found a dislocated or fractured hip. Sweating profusely, you and your team use a scoop stretcher to extricate the patient out of the house and into the air-conditioned unit. Making the scene safer for the patient, through extrication, is an important immediate treatment action.

Inside the ambulance the patient’s clothing is removed and ice packs are placed in her groin and armpits. A rectal thermometer reveals a temperature of 42.8 C (109 F). She is hypotensive and tachycardic. A large bore IV is established in the left antecubital vein and a liter of lactated ringers is rapidly administered during transport. After transferring the patient to the emergency department, the patient undergoes further invasive cooling and is admitted to the ICU, where she remains for several weeks.

Community education and injury prevention

Hot weather and high humidity forecasts create an opportunity for community education and injury prevention. Paramedics may consider deploying in neighborhoods with a high number of geriatric patients to conduct welfare checks and encourage residents to go to air conditioned public buildings. Community paramedics, as they consult a patient on their chronic illness and medications, can educate patients on their increased risk for hyperthermia.


  1. Semenza, J. C., C. H. Rubin, K. H. Falter, et al. Heat-related deaths during the July 1995 heat wave in Chicago. N. Engl. J. Med. 335:84-90, 1996.
  2. Robine JM, Cheung SL, Le Roy S, Van Oyen H, Griffiths C, Michel JP, Herrmann FR. Death toll exceeded 70,000 in Europe during the summer of 2003. C R Biol. 2008 Feb;331(2):171-8.
  3. Haider, Kamran; Anis, Khurrum. Heat Wave Death Toll Rises to 2,000 in Pakistan’s Financial Hub. Bloomberg News. 24 June 2015.
  4. Carter R 3rd, Cheuvront SN, Williams JO, Kolka MA, Stephenson LA, Sawka MN, Amoroso PJ. Epidemiology of hospitalizations and deaths from heat illness in soldiers. Med Sci Sports Exerc. 2005 Aug;37(8):1338-44.
  5. Larach MG, Brandom BW, Allen GC, Gronert GA, Lehman EB. Cardiac arrests and deaths associated with malignant hyperthermia in north america from 1987 to 2006: a report from the north american malignant hyperthermia registry of the malignant hyperthermia association of the United States. Anesthesiology. 2008 Apr. 108(4):603-11.
  6. Helman RS. Heat Stroke. Medscape: retrieved 15 October 2015.
  7. Erickson TB, Prendergast HM. Procedures pertaining to hyperthermia. Roberts JR, Hedges JR, Chanmugan AS, et al. Clinical Procedures in Emergency Medicine. 4th ed. WB Saunders; 2004. 1358-70.

Art Hsieh, MA, NRP teaches in Northern California at the Public Safety Training Center, Santa Rosa Junior College in the Emergency Care Program. An EMS provider since 1982, Art has served as a line medic, supervisor and chief officer in the private, third service and fire-based EMS. He has directed both primary and EMS continuing education programs. Art is a textbook writer, author of “EMT Exam for Dummies,” has presented at conferences nationwide and continues to provide direct patient care regularly. Art is a member of the EMS1 Editorial Advisory Board. Contact Art at and connect with him on Facebook or Twitter.