The Quick and Dirty Guide to Hyperthermia Q&D guide to hyperthermia

Environmental emergencies can be life threatening to potential victims; not to mention quite challenging for EMS professionals. When the potential for an environmental emergency exists, EMS professionals must consider the following factors:

  • Localized prevailing weather norms and any deviations
  • Seasonal variations in climate
  • Weather extremes potential (i.e., wind, rain, snow, humidity)
  • Barometric pressure (i.e., altitude, underwater)
  • Terrain that can worsen the emergency/delay the response

The patients health is also a factor related to environmental stressors. It can potentially make the illness/injury worse. Examples include the patient's age, predisposing medical conditions, use of prescription/OTC drugs, and use of alcohol.


Hyperthermia, or heat illness, results from one of two basic causes:

  1. Temperature regulating mechanisms are overwhelmed by high environmental temperatures or, more commonly, by excessive activity/exercise in moderate/high temperatures.
  2. Temperature regulation centers in the hypothalamus fail, seen usually in older/ill or incapacitated patients.

Regardless of the cause, it can result in heat illnesses such as heat cramps, heat exhaustion, and heat stroke.

Heat Cramps

Heat Cramps consists of benign muscle cramping 2° to dehydration and is not associated with an elevated temperature.

Heat cramps are often brief, intermittent, and often severe muscle cramps that occurs in muscles fatigued by heavy work or exertion. The primary cause of heat cramps is the excessive loss of water and sodium. People who suffer from heat cramps sweat profusely and normally drink water with out replenishing the sodium that is being lost. In higher environmental temperatures the body can loss 1 to 3 liters per hour from sweating (evaporation). Each liter of body fluid that is lost contains 30 -50 mEq of sodium chloride (salt). It is a combination of the fluid and salt loss that initiates the cramping. Cramping usually occurs in the large muscle groups of the legs and arms, although any muscle may be involved.

Symptoms include:

  • Hot/ sweaty skin
  • Tachycardia
  • Normal BP
  • Core body temperature remains normal.

Heat Exhaustion

Heat Exhaustion consists of dehydration, salt depletion, dizziness, fever, mental status changes, headache, cramping, nausea and vomiting. Vital signs usually consist of tachycardia, hypotension, and an elevated temperature.

Heat exhaustion is a more severe form of heat illness , it is characterized by:

  • Changes in mental status (i.e., irritability and poor judgement)
  • Dizziness
  • Nausea
  • Headache
  • Mild/moderate elevation in core body temperature (up to 103* F {39*C})

In severe cases, dizziness/syncope can occur from a significant intravascular volume loss. Orthostatic dizziness may occur when the patient changes from a lying position to a sitting or standing position. Like heat cramps, heat exhaustion is more often associated with a hot environment that results from extreme sweating. Loss of water and salt, electrolyte imbalance, and difficulty maintaining blood pressure can greatly contribute to the problem. The patient shows signs of inadequate peripheral and cerebral perfusion. Patients normally recover quickly when removed from the hot environment and fluids are replenished. Heat exhaustion can quickly progress to heat stroke, if left untreated.

Heat Stroke

Heat Stroke consists of dehydration, tachycardia, hypotension, temperature >104° F (40° C), and an altered mental status.

Heat stroke occurs when the body temperature-regulating mechanisms breakdown down entirely. As a result of this failure, the body temperature rises to 105.8* F (41* C) or higher. This is enough to damage tissues in all the body systems, resulting in a systemic body system collapse. Increased body temperature caused by failure of the temperature regulating mechanisms should not be confused with a fever caused by inflammation or infection. Heat stroke is a true medical emergency, that can be classified in 2 types.

Classic heat stroke occurs during periods of sustained high ambient temperatures and humidity. Victims of classic heat stroke may also suffer from chronic illness that may worsen the syndrome. In contrast, patients with exertional heat stroke are usually young and healthy. In this situation, the heat builds up rapidly in the body quicker than be dispensed into the environment (sweating-evaporation). The temperature regulating centers in the brain, receive their information largely from the temperature of the circulating blood and skin. In response to hypothalamic stimulation, a number of physiological events occur:

  1. Respiratory rate quickens to help increase heat loss through the exhaled air.
  2. Cardiac output increases to provide more blood flow through skin and muscle to enhance heat radiation.
  3. Sweat gland activity increases to enhance evaporative heat loss.

All these compensatory mechanisms require a normally functioning CNS to be able to properly respond to the temperature extreme. They also need a functioning cardiovascular system to be able to bring some of the heat to the surface in the blood.

The CNS manifestations of heat stroke varies, some patients may become comatose. Others may present with confusion and irritability before becoming unconscious. Convulsions are common, and occur early or late in the course f the illness. Because the brain stores very little energy, it depends on the continuous delivery of oxygen and glucose to function properly. Decreased cerebral perfusion pressure results in cerebral ischemia and acidosis. The increased temperatures markedly increases the metabolic demands of the brain as well. The extent of brain damage depends on the severity and duration of the hyperthermic episode.

A rise in skin temperature reduces the thermal gradient between the core and the skin causing an increase in skin blood flow (peripheral vasodilation), giving the skin a flushed appearance. About 25% of all exertional heat stroke victims will have a flushed appearance, and profuse sweating which occurs as a result of an increased release of catecholamines. Classic heat stroke victims are normally "all sweated out", therefore sweating is normally absent. this is mainly due to dehydration. Therefore the presence of sweating does not rule out the diagnosis. Q&D guide to hyperthermia

The cessation of sweating is not the cause of a heat stroke. Peripheral vasodilation results in a decrease in vascular resistance and shunting of the blood, is also common, as the condition progresses. High output cardiac failure can occur, characterized by tachycardia and hypotension. Cardiac output can initially be increased to four or five times it's normal. However, as the temperatures continue to rise, myocardial contractibilty begins to decrease and central venous pressures begin to rise. The effect of heat stress on cardiac output can be fatal if not recognized and cooling techniques not initiated.

In any age group a heat emergency patient that presents as hypotensive with a decreased cardiac output, points to a poor prognosis, if intervention isn't immediate. There are other systemic manifestations that may be present:

  • Pulmonary edema
  • Systemic acidosis
  • Tachynpea
  • Hypoxemia
  • Hypercapnia
  • GI bleed
  • Clotting disorders
  • Electrolyte imbalances


Heat Illness Management

The most important factors to obtain a successful outcome for the victim, is to initiate the basics (BLS) quickly, very quickly, while awaiting ALS interventions. Recognizing that a heat illness is occurring is key in initiating the proper rapid intervention.

  • Move the patient out of the heated environment into a cooler location before initiating treatment.
  • Obtain and document patient temperature if able.
  • Recommended Exam: Mental Status, Skin, HEENT, Heart, Lungs, Neuro · Extremes of age are more prone to heat emergencies (i.e. young and old).
  • Rapid cooling is indicated for patients with symptoms indicative of heat stroke. Cooling measures should include removing patient clothing/coverings. Evaporative cooling by wetting the patient’s skin and using fanning to move air around the patient is most effective.
  • Cold packs to the axilla and groin may also assist with cooling.
  • Do not stimulate shivering
  • Cooling measures as indicated for patients with symptoms indicative of heat exhaustion. These patients are most likely to be active, healthy individuals in need of hydration due to increased exertion and fluid loss from perspiration.
  • Treat for shock, elevate feet if trauma is not possible.
  • P.O. fluids may be given to patients with suspected heat exhaustion or heat cramps only; if the patient has a gag reflex and does not present with an altered level of conscious. Give small sips of water or electrolyte solutions only (Hold up, if the patient develops nausea).
  • Monitor patients vitals and EKG for the onset of heat related dysrhythmias.


Cardiac Rhythms in Heat Stroke Cardiac Rhythms during Heat Stroke


  • Heat illness that is predisposed by use of: tricyclic antidepressants, phenothiazines, anticholinergic medications, and alcohol
  • Cocaine, Amphetamines, and Salicylates may elevate body temperatures
  • Sweating generally disappears as body temperature rises above 104° F (40° C).
  • Intense shivering may occur as patient is cooled

A cool short video for understanding heat illness!



 For more information on you can also check out:

Heat Safety from OSHA



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