Heat stroke, also known as sun stroke, is a type of severe heat illness that results in a body temperature greater than 40.0 °C (104.0 °F) and confusion. Other symptoms include red, dry or damp skin, headache, and dizziness. Onset can be sudden or gradual. Complications may include seizures, rhabdomyolysis, or kidney failure.
Heat stroke occurs because of high external temperatures or physical exertion. Risk factors include heat waves, high humidity, certain drugs such as diuretics, beta blockers, or alcohol, heart disease, and skin disorders. Cases not associated with physical exertion typically occur in those at the extremes of age or with long term health problems. Diagnosis is based on symptoms. It is a type of hyperthermia. It is distinct from a fever, where there is a physiological increase in the temperature set point.
Preventive measures include drinking sufficient fluids and avoiding excessive heat. Treatment is by rapid physical cooling of the body and supportive care. Recommended methods include spraying the person with water and using a fan, putting the person in ice water, or giving cold intravenous fluids. While it is reasonable to add ice packs around a person, this by itself is not routinely recommended.
It results in more than 600 deaths a year in the United States. Rates have increased between 1995 and 2015. The risk of death is less than 5% in those with exercise-induced heat stroke and as high as 65% in those with non-exercise induced cases.
Signs and symptoms
Heat stroke generally presents with a hyperthermia of greater than 40.6 °C (105.1 °F) in combination with disorientation and a lack of sweating. Before a heat stroke occurs, people show signs of heat exhaustion such as dizziness, mental confusion, headaches, and weakness; if a heat stroke occurs when the person is asleep, symptoms may be harder to notice. However, in exertional heat stroke, the affected person may sweat excessively. Young children, in particular, may have seizures. Eventually, unconsciousness, organ failure, and death will result.
Heat stroke occurs when thermoregulation is overwhelmed by a combination of excessive metabolic production of heat (exertion), excessive environmental heat, 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. Exertional heat stroke (EHS) can happen in young people without health problems or medications – most often in athletes, outdoor laborers, or military personnel engaged in strenuous hot-weather activity or in certified first responders wearing heavy personal protective equipment. In environments that are not only hot but also humid, it is important to recognize that humidity reduces the degree to which the body can cool itself by perspiration and evaporation. For humans and other warm-blooded animals, excessive body temperature can disrupt enzymes regulating biochemical reactions that are essential for cellular respiration and the functioning of major organs.
When the outside temperature is 21 °C (70 °F), the temperature inside a car parked in direct sunlight can quickly exceed 49 °C (120 °F). Young children or elderly adults left alone in a vehicle are at particular risk of succumbing to heat stroke. “Heat stroke in children and in the elderly can occur within minutes, even if a car window is opened slightly.” As these groups of individuals may not be able to open car doors or to express discomfort verbally (or audibly, inside a closed car), their plight may not be immediately noticed by others in the vicinity.
Dogs are even more susceptible than humans to heat stroke in cars, as dogs cannot produce whole-body sweat to cool themselves. Leaving the dog at home with plenty of water on hot days is recommended instead, or, if a dog must be brought along, it can be tied up outside the destination and provided with a full water bowl.
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.
The Occupational Safety and Health Administration in the United States publishes a QuickCard with a checklist designed to help protect workers from heat stress:
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.
The body temperature must be lowered quickly. The person should be moved to a cool area (indoors, or at least in the shade) and clothing removed to promote heat loss (passive cooling). Active cooling methods should also be used, if possible: The person is bathed in cold water, or a hyperthermia vest can be applied. (However, wrapping the person in wet towels or clothes can actually act as insulation and increase the body temperature.) Cold compresses to the torso, head, neck, and groin will help cool the victim. A fan or dehumidifying air-conditioning unit may be used to aid in evaporation of the water (evaporative method).
Immersing a person into a tub of cold water (immersion method) is a widely recognized method of cooling. 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, this hypothesis has been challenged in experimental studies, as well as by systematic reviews of the clinical data, indicating that cutaneous vasoconstriction and shivering thermogenesis do not play a dominant role in the decrease in core body temperature brought on by cold water immersion. This can be seen in the effect of submersion hypothermia, where the body temperature decrease is directly related to environmental temperature, and though bodily defenses slow the decrease in temperature for a time, they ultimately fail to maintain endothermic homeostasis. Dantrolene, a direct-acting paralytic which abolishes shuddering and is effective in many other forms of hyperthermia, including centrally-, peripherally- and cellularly-mediated thermogenesis, has no individual or additive effects to cooling in the context of heat stroke, showing a lack of endogenous thermogenic response to cold water immersion. Thus, aggressive ice-water immersion remains the gold standard for life-threatening heat stroke.
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 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.
In India, hundreds die every year from summer heat waves, including more than 2,500 in the year 2015. Later that same summer, the 2015 Pakistani heat wave caused about 2,000 deaths.
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.