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    Wednesday, July 8, 2009


    Everyone is at risk for Heatstroke in times of extreme heat, those who are exerting themselves, but also those sitting quietly in the sun. Heat stroke is defined as a core body temperature in excess of 40.5ºC (105ºF) with associated central nervous system dysfunction in the setting of a large environmental heat load that cannot be dissipated

    The truth is, you can develop heat stroke while sitting perfectly still, if you have certain risk factors like chronic medical conditions or use certain medications.
    Hyperthermia is defined as elevation of core body temperature above the normal range of body temperature. Body temperature is maintained within a narrow range by balancing heat load with heat dissipation. The body's heat load results from both metabolic processes and absorption of heat from the environment. As core temperature rises, the the autonomic nervous system is stimulated to produce sweating and cutaneous vasodilation.

    Evaporation is the principal mechanism of heat loss in a hot environment, but this becomes ineffective above a relative humidity of 75 percent. The other major methods of heat dissipation — radiation (emission of infrared electromagnetic energy), conduction (direct transfer of heat to an adjacent, cooler object), and convection (direct transfer of heat to convective air currents) — cannot efficiently transfer heat when environmental temperature exceeds skin temperature.

    In other words when it gets hot and needs to pump faster, hearts weakened by heart disease may be unable to get the body cooled fast enough. People with high blood pressure or hypertension also experience greater stress on the heart, and hypertension sufferers often follow low-salt diets. Not having enough salt in your system can lower the threshold for heat stroke. People with diabetes can also easily become dehydrated, which keeps the body from sweating normally, and obesity not only puts extra pressure on the heart, but it also must work even harder to cool down a larger person.

    Medications like diuretics (water pills) reduce the amount of fluid in the body and lead to easier dehydration. Beta blockers, often used to treat heart problems, can also prevent the heart from beating faster, thus inhibiting the body's cooling system. Older people are especially at risk for these factors affecting how your body reacts to the heat. Untreated heat exhaustion can lead to heat stroke, which is signified by a rapid heartbeat, confusion or even delirium, a fever of greater than 104 degrees, severe headaches and seizures or muscle twitching. The skin of a heat stroke victim will be warm and dry, because the body is no longer able to perspire.

    The reason is --Your body must maintain its normal temperature to work well. When it gets hot, your body begins to cool itself by sweating. Your body cools as the perspiration evaporates. In order to get more blood to the skin's surface and aid sweating, the heart will beat faster. This occurs even if you're sitting still in the sun.If your body is unable to rid itself of excess heat, your organs can begin to overheat and stop working. This is called heat stroke, and can result in confusion, seizures, permanent disabilities, multiorgan system failure, acute respiratory distress syndrome (ARDS), disseminated intravascular coagulation, renal, hepatic failure, hypoglycemia, rhabdomyolysis, seizures and death.

    Physical findings in heat stroke may include cutaneous vasodilation, tachypnea, rales due to noncardiogenic pulmonary edema, excessive bleeding due to disseminated intravascular coagulation, and evidence of neurologic dysfunction such as altered mentation or seizures. The skin may be moist or dry, depending upon underlying medical conditions, the speed with which the heat stroke developed, and hydration status. Not all victims of heat stroke should be assumed to be volume-depleted. Laboratory studies may reveal coagulopathy, acute renal failure, acute hepatic necrosis, respiratory alkalosis, and a leukocytosis as high as 30,000 to 40,000/mm3.

    Warning signs for heat stroke or exhaustion are dizziness or fainting, excessive sweating, muscle cramps, cold or clammy skin, headaches, rapid heartbeat or nausea. If you experience any of these, get out of the heat right away, drink water, juice or sports drinks and seek medical attention.

    The risk of serious consequences can be reduced with a few simple precautions. If you have A chronic medical conditions discussed, try to get out of the sun sooner than others, and avoid outdoor activities during the hottest times of day. Wear loose fitting clothes and unless otherwise directed, get plenty of extra fluids (like water, but avoid alcoholic or caffeinated beverages).

    Cooling measures — Augmentation of evaporative cooling is considered the treatment modality of choice because it is effective, noninvasive, and easily performed. The naked patient is sprayed with a mist of lukewarm water while air is circulated with large fans. Shivering may be suppressed with intravenous benzodiazepines such as diazepam (5 mg IV) or lorazepam (1-2 mg IV) or, if NMS is not suspected, with chlorpromazine (25 to 50 mg IV).

    Other effective cooling methods are less commonly utilized. Immersing the patient in ice water is the most effective method of rapid cooling. Immersing the patient in ice water results in rapid cooling but complicates monitoring and access. Applying ice packs to the axillae, neck, and groin is effective, but is poorly tolerated in the awake patient.

    Please remember, as with all our articles we provide information, not medical advice.
    For any treatment of your own medical condition you must visit your local doctor, with or without our article[s]. These articles are not to be taken as individual medical advice.

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