Heat Illnesses

Characteristics of condition

Differential diagnoses


Heat syncope

Cardiac arrest

Exertional heat stroke

Heat exhaustion

Exercise-associated collapse


Orthostatic dizziness after standing in one place for prolonged time in the heat

Loss of cardiac function often due to cardiac dysrhythmias

Severe heat illness caused by increased metabolic heat production and/or inability to dissipate heat

Inability to continue exercise in the heat, often due to cardiac insufficiency and fluid and/or electrolyte depletion

Collapse in a conscious athlete that is unable to walk or stand [23] Occurs when the individual abruptly stops during intense exercise

Initial signs and symptoms

Fainting, hypotension

Unresponsive, lack of pulse, not breathing

Collapse and/or CNS dysfunction (acting out of sorts, combativeness, coma), rectal temperature >104 °F

Fatigue, pallor, weakness, headache, vomiting, dizziness

Inability to stand without assistance after cessation of exercise, dizziness, hypotension

Diagnostic criteria/ ruling “in”

Syncope in unacclimatized individual that has been standing for a long time, rectal temperature <104 °F, rapid, weak pulse, initially hypotensive

Unresponsive, no pulse, not breathing, no signs of life

CNS dysfunction and rectal temperature >104 °F following exercise in the heat. Can be associated with organ-system dysfunction

Symptoms above in an individual that is not heat acclimatized and has been exercising in the heat. Rectal temperature <104 °F and minimal or no CNS dysfunction

Collapse and orthostatic intolerance in individual that has abruptly stopped exercising


Elevate legs, monitor vital signs, move to cooler area and rehydrate

Activate EMS, CPR, AED

Aggressive cooling via cold water immersion until temperature reaches 102 °F

Move to cooler area, rehydrate if possible, cool the skin via ice towels, fanning, etc.

Elevate legs, monitor vital signs, move to cooler area, and rehydrate

CNS central nervous system, EMS emergency medical services, CPR cardiopulmonary resuscitation, AED automated external defibrillator


Recognition of heat syncope and ruling out a more serious condition is critical for the healthcare provider. There are various causes of collapse in an exercising individual; therefore the clinician’s primary goal is to rule out cardiac arrest or other life-threatening causes of collapse (i.e., exertional heat stroke, head injury, exertional sickling). Initial assessment of an athlete that has experienced syncope should include assessment of responsiveness, breathing, and heart rate [7]. Proper recognition of heat syncope consists of recognizing the symptoms, which may include dizziness, tunnel vision, a brief episode of fainting, and pale skin [7]. Once an acute cardiac etiology is ruled out, the clinician should ensure the patient is not experiencing exertional heat stroke. The key to ruling out exertional heat stroke is that with heat syncope, core body temperature will typically remain below 40 °C (104 °F), whereas with exertional heat stroke (EHS), patients will have a dangerously elevated core body temperature, often greater than 104 °F. Those with EHS will also have an altered mental status. After a fainting episode, patients typically regain a normal mental status. The treatment for these conditions is vastly different; therefore, ruling out more serious conditions and confirming the diagnosis of heat syncope is extremely important.


Treatment for heat syncope is similar to other syncopal episodes. Once more serious metabolic, cardiovascular, or neurologic disorders have been ruled out (i.e., primary survey), the patient should be placed in the Trendelenburg position, and vital signs should be monitored. If possible, the patient should be moved to a cooler area (air-conditioned or shaded area), and fluids should be given orally when the patient has regained consciousness and is coherent [7]. Attempts to cool via nonaggressive cooling methods (i.e., fanning, ice towels) may improve the patient’s status; however, more aggressive cooling, such as cold water immersion, is not necessary since body temperature will not be dangerously elevated with heat syncope. Emphasis in treating a heat syncope patient should be placed on restoring cardiovascular function and ensuring signs and symptoms are no longer present.

Return to Activity

Return to exercise following heat syncope requires three important steps. Primarily, a more serious condition such as cardiac, EHS, or sickling should be ruled out. Secondly, healthcare providers should ensure all signs and symptoms from the syncopal episode have resolved. This would include normal vital signs, primarily blood pressure and heart rate, and restoration of normal hydration status. Lastly, the cause of the heat syncope should be determined and addressed prior to return to activity. If the patient lacked heat acclimatization prior to the syncopal episode, a gradual progression of heat exposure across 7–10 days should be introduced. The patient’s hydration status should be measured via body mass changes or urinary field markers, such as urine color or specific gravity, to ensure the patient is euhydrated prior to being reintroduced to the warm environment. Additionally, it is imperative to educate the patient on maintaining a proper diet. If any of the signs or symptoms has not resolved or heat syncope should reoccur, the patient should be referred for a more extensive follow-up with a physician.


Understanding the development, pathophysiology, recognition, and treatment of minor heat illnesses is important for medical professionals. While minor heat illnesses lack the severity associated with exertional heat stroke and other medical emergencies, treating minor heat illnesses appropriately can enhance the acclimatization process and prevent the development of exertional heat illnesses.

Nov 7, 2020 | Posted by in SPORT MEDICINE | Comments Off on Heat Illnesses

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