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Heat Illness Part 1

Mizuho Morrison, DO and Matthieu DeClerck, MD

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With the hot summer months it is important to understand and be able to differentiate between various types of heat illnesses. Mizuho Spangler and Matthieu Declerck discuss the diagnosis, management and treatments for these various heat illnesses.


  • A Temperature greater than 104 degrees Fahrenheit or mental status changes can differentiate heat stroke from less serious heat related illnesses.

  • Rapid immersion in cold water is the most important management step in heat stroke.


Heat related illness can be broken down into six general categories


  • What is heat rash? Heat rash has a number of names including “sweat rash”, “heat rash”, and  “miliaria rubra”.  

    • In this condition sweat glands that get clogged up by the debris from the stratum corneum leading to local inflammation and a painful or pruritic rash that consists of small red papules.

    • Treatment is with loose fitting clothing, avoiding moisturizers. which can contribute to occlusion of the sweat glands. When more significant inflammation is present a topical steroid or non-steroidal anti-inflammatories can be used.

  • What is heat edema? The body’s response to heat includes peripheral vasodilation and an increased heart rate in an effort to shed heat. These two factors can lead to peripheral edema. This could be more likely in those already predisposed to edema and the treatment is to remove the patient from the heat.

  • What are heat cramps? Heat cramps are also known a exercise-associated cramps and are localized cramps that occur in the context of exertion. The role of heat in the pathogenesis is not completely established. They are likely caused by a local electrolyte imbalance and dehydration also plays a role. The treatment is rest, massage, getting out of the heat and hydration. They should self resolve and not be associated with pain out of proportion to exam or muscle spasms.

  • What is heat syncope?

    • The classic case is a soldier standing out in the hot parade who passes out and falls down. In this case peripheral vasodilation causes venous pooling reduced blood flow to the brain and syncope.

    • Another situation is so- called  “exercise associated collapse”. This is classically the marathon runner who collapses after finishing the race and is caused by a sudden decrease in the pressure provided on the venous structures by skeletal muscle leading to an abrupt drop in venous return and collapse.

    • The final scenario is someone who has been seated for a long time in the heat and has an episode of syncope upon standing up the mechanism of which is similar to that in the case of the first example with the added positional change.

    • The key factor distinguishing heat syncope from the more dangerous heat exhaustion or heat stroke is elevation of core temperature and mental status alteration. In heat syncope, the patient's core temperature should either be normal or only slightly elevated and their mental status should either be normal or quickly improve within minutes of their syncopal event.

  • How do we differentiate more benign heat illness from heat stroke? The distinction is important as heat stroke can have mortality ranging from 30 to 80% if not quickly reversed. Both the temperature and mental status can differentiate the two. In heat stroke the temperature should be greater than 104 oF  and they will have altered mental status.

    • In heat exhaustion we expect core body temperature that is elevated, anywhere from 101 to 104 oF or 38.3 to 40o C at the time of collapse. Patients may have nausea, vomiting, muscle cramping, sweating or weakness. They may be tachycardic and even hypotensive but should not have altered mental status.

  • How do me manage heat exhaustion? Management is with hydration either intravenous or oral and cooling. Remove the patient for the heat, removing clothing or sports equipment that is limiting evaporation. This facilitates evaporative cooling and may be all that is needed. Evaporative cooling can be done misting with water and circulating the surrounding air with a fan.

  • Is there a role for antipyretics in heat illness? Because of a different mechanism of the temperature non-steroidals and acetaminophen will not be effective.

  • What is heat stroke? The diagnosis of heatstroke includes having a core body temperature above 104o F or 40o C and having altered mental status or central nervous system dysfunction.

    • Practically speaking it is difficult to get a core temperature in the field and this diagnosis is typically suspected based on the altered mental status. The altered mental status is caused by heat related brain edema.

    • Heat-illnesses is the third major cause of death (behind traumatic and cardiac causes) in teenage athletes that can occur during the physical activity.

    • Cerebral edema is caused by denaturing of the proteins in the brain, and leaking of the blood-brain barrier. In the gut there is endothelial leakage, which can lead to sepsis. Coagulopathies and liver failure occur along with elevated LFTs. Kidney injury can occur from rhabdomyolysis and hypovolemia. Cardiomyopathies can occur related to heat related breakdown of muscle tissue. Finally Acute Respiratory Distress Syndrome can also occur

  • What is the treatment of heat stroke? Rapid immersion in cool water. Liquid medium is much more effective than air in dissipating heat. Ice water is preferred but cool water is the next best thing.

    • In the pre-hospital setting management includes removing clothing, transporting the patient to the shade, misting with water, fanning and applying cool packs to the groin and neck near large vessels..   

  • How do we prevent heat illness?

    • When there are higher temperatures make sure that pets, children, and older adults are not in that hot environment. Keep kids out of hot cars and make sure to maintain hydration. With the exertional component of these illnesses moving athletics insider or later in the day when heat is worse can prevent illness. Frequent breaks should also be encouraged.

    • Acclimatization can also help prevent heat related illness. This is traditionally done with one to two hours of exertion in a hot environment for 10-14 days. This leads the body to tolerate heat better with physiologic changes including sweeting earlier in exertion.

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