Heat stroke

Heat stroke generally presents with a hyperthermia of greater than 40.6 °C (105.1 °F) in combination with disorientation.[5][9] However, high body temperature does not necessarily indicate that heat stroke is present, such as with people in high-performance endurance sports or with people experiencing fevers.[10] Exertional heat stroke is more accurately diagnosed based on a constellation of symptoms rather than just a specific temperature threshold.[10] There is generally a lack of sweating in classic heatstroke, while sweating is generally present in exertional heatstroke.[5]

Early symptoms of heat stroke include behavioral changes, confusion, delirium, dizziness, weakness, agitation, combativeness, slurred speech, nausea, and vomiting.[5] In some individuals suffering from exertional heatstroke, seizures, and sphincter incontinence have also been reported.[5] Additionally, in exertional heat stroke, the affected person may sweat excessively.[11] If treatment is delayed, patients could develop vital organ damage, unconsciousness and even organ failure. In the absence of prompt and adequate treatment, heatstroke can be fatal.[12]

Heat stroke occurs when thermoregulation is overwhelmed by a combination of excessive metabolic production of heat (exertion), excessive heat in the physical environment, and insufficient or impaired heat loss, resulting in an abnormally high body temperature. Substances that inhibit cooling and cause dehydration such as alcohol, stimulants, medications, and age-related physiological changes predispose to so-called "classic" or non-exertional heat stroke (NEHS), most often in elderly and infirm individuals in summer situations with insufficient ventilation.[13]

The pathophysiology of heat stroke involves an intense heat overload followed by a failure of the body's thermoregulatory mechanisms. More specifically, heat stroke leads to inflammatory and coagulation responses that can damage the vascular endothelium and result in numerous platelet complications, including decreased platelet counts, platelet clumping, and suppressed platelet release from bone marrow.[17]

Growing evidence also suggests the existence of a second pathway underlying heat stroke that involves heat and exercise-driven endotoxemia.[18] Although its exact mechanism is not yet fully understood, this model theorizes that extreme exercise and heat disrupt the intestinal barrier by making it more permeable and allowing lipopolysaccharides (LPS) from gram-negative bacteria within the gut to move into the circulatory system.[18] High blood LPS levels can then trigger a systemic inflammatory response and eventually lead to sepsis and related consequences like blood coagulation, multi-organ failure, necrosis, and central nervous system dysfunction.[18]

The risk of heat stroke can be reduced by observing precautions to avoid overheating and dehydration. Light, loose-fitting clothes will allow perspiration to evaporate and cool the body. Wide-brimmed hats in light colors help prevent the sun from warming the head and neck. Vents on a hat will help cool the head, as will sweatbands wetted with cool water. Strenuous exercise should be avoided during hot weather, especially in the sun peak hours as well as avoiding confined spaces (such as automobiles) without air-conditioning or adequate ventilation.

In hot weather, people need to drink plenty of cool liquids and mineral salts to replace fluids lost from sweating. Thirst is not a reliable sign that a person needs fluids. A better indicator is the color of urine. A dark yellow color may indicate dehydration.[11]

Example of a checklist designed to help protect workers from heat stress:[19]

• Know signs/symptoms of heat-related illnesses.
• Block out direct sun and other heat sources.
• Drink fluids often, and before you are thirsty.
• Wear lightweight, light-colored, loose-fitting clothes.
• Avoid beverages containing alcohol or caffeine.

Treatment of heat stroke involves rapid mechanical cooling along with standard resuscitation measures.[20]

The body temperature must be lowered quickly via conduction, convection, or evaporation.[4] The person should be moved to a cool area, such as indoors or to a shaded area. Clothing should be removed to promote heat loss through passive cooling. Conductive cooling methods such as ice-water immersion should also be used, if possible. Evaporative and convective cooling by a combination of cool water spray or cold compresses with constant air flow over the body, such as with a fan or air-conditioning unit, is also an effective alternative.[4] The person should not be wrapped in wet towels or clothing as this can act as insulation and increase the body temperature.

Aggressive ice-water immersion remains the gold standard for life-threatening heat stroke.[21][22] This method may require the effort of several people and the person should be monitored carefully during the treatment process. Immersion should be avoided for an unconscious person, but if there is no alternative, the person's head must be held above water.

Immersion in very cold water was once thought to be counterproductive by reducing blood flow to the skin and thereby preventing heat from escaping the body core. However, research has shown that this mechanism does not play a dominant role in the decrease in core body temperature brought on by cold water. Dantrolene, a muscle relaxant used to treat other forms of hyperthermia, is not an effective treatment for heat stroke.[23]

Hydration is important in cooling the person. In mild cases of concomitant dehydration, this can be achieved by drinking water, or commercial isotonic sports drinks may be used as a substitute. In either exercise- or heat-induced dehydration, electrolyte imbalance can result, and can be worsened by excess consumption of water. Hyponatremia can be corrected by intake of hypertonic fluids. Absorption is rapid and complete in most people but if the person is confused, unconscious, or unable to tolerate oral fluid, then an intravenous drip may be necessary for rehydration and electrolyte replacement.

The person's condition should be reassessed and stabilized by trained medical personnel. The person's heart rate and breathing should be monitored, and CPR may be necessary if the person goes into cardiac arrest.

It was long believed that heat strokes lead only rarely to permanent deficits and that convalescence is almost complete. However, following the 1995 Chicago heat wave, researchers from the University of Chicago Medical Center studied all 58 patients with heat stroke severe enough to require intensive care at 12 area hospitals between July 12 and 20, 1995, ranging in age from 25 to 95 years. Nearly half of these patients died within a year – 21 percent before and 28 percent after release from the hospital. Many of the survivors had permanent loss of independent function; one-third had severe functional impairment at discharge, and none of them had improved after one year. The study also recognized that because of overcrowded conditions in all the participating hospitals during the crisis, the immediate care – which is critical – was not as comprehensive as it should have been.[24]

In rare cases, brain damage has been reported as a permanent sequela of severe heat stroke, most commonly cerebellar atrophy.[25][26]

In India, hundreds die every year from summer heat waves,[27] including more than 2,500 in the year 2015.[28] Later that same summer, the 2015 Pakistani heat wave caused about 2,000 deaths.[29]

In Slavic mythology, there is a personification of sunstroke, Poludnitsa (lady midday), a feminine demon clad in white that causes impairment or death to people working in the fields at midday. There was a traditional short break in harvest work at noon, to avoid attack by the demon. Antonín Dvořák's symphonic poem, The Noon Witch, was inspired by this tradition.

Heatstroke can affect livestock, especially in hot, humid weather; or if the horse, cow, sheep or other is unfit, overweight, has a dense coat, is overworked, or is left in a horsebox in full sun. Symptoms include drooling, panting, high temperature, sweating, and rapid pulse.

The animal should be moved to shade, drenched in cold water and offered water or electrolyte to drink.[30]

• Heat exhaustion
• Occupational heat stress

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