Heat stroke

"Heatstroke" and "Heatstrokes" redirect here. For the film, see Heatstroke. For the song by Krokus, see Metal Rendez-vous.

Heat stroke
Classification and external resources
Specialty
ICD-10	T67.0
ICD-9-CM	992.0
DiseasesDB	5690
MedlinePlus	000056
eMedicine	med/956
Patient UK	Heat stroke
MeSH	D018883

Heat stroke, also known as sun stroke, is a severe heat illness, defined as hyperthermia with a body temperature greater than 40.6 °C (105.1 °F) because of environmental heat exposure with lack of thermoregulation. This is distinct from a fever, where there is a physiological increase in the temperature set point of the body. The term "stroke" in "heat stroke" is a misnomer in that it does not involve a blockage or hemorrhage of blood flow to the brain. Preventive measures include drinking plenty of cool liquids and avoiding excessive heat and humidity, especially in unventilated spaces such as parked cars that can overheat quickly. Treatment requires rapid physical cooling of the body.

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. 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.

Causes

Biological

See also: Hyperthermia § Causes

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 or 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.

Children and pets in cars

Between 1998 and 2011, at least 500 children in the United States died from being inside hot cars, and 75% of the victims were less than 2 years old. 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, elderly adults, or disabled individuals left alone in a vehicle are at particular risk of succumbing to heat stroke, even when the windows are left partially open. 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. A stuffed toy or other child's toy is recommended for a parent or guardian to keep with himself or herself in the front seat as a reminder that at least one child is present. For larger groups in a van or bus, checking for stragglers at the end of the trip is essential, complemented by other procedures such as a head count.

Pets are even more susceptible than humans to heat stroke in cars, as dogs (the animals usually involved), cats and many other animals cannot produce whole-body sweat to cool themselves. Pets are prohibited from being brought into many establishments, and opening a vehicle window sufficiently may pose a risk of escape, bite or theft. Leaving the pet 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.

Among recent child deaths in hot cars, approximately half occurred because parents forgot that the child was in the car, 18% happened after parents intentionally left the child in the car without understanding how hot it could get, and 30% happened after the child climbed into the car to play. Legal prosecution of parents in these situations can vary greatly. In separate incidents, a college professor in California forgot that his son was in a hot car, and a horse groomer in Florida knowingly left his daughter in his car during horse races. Each resulted in the unintentional death of a child, but the college professor was never prosecuted, while the horse groomer was sentenced to 20 years in prison followed by deportation.

Forgotten baby syndrome

"Forgotten baby syndrome" is a pseudo-medical term for the danger of adult caregivers forgetting about the presence of a young child and consequently subjecting the child to danger. In spite of the word "syndrome", this is not a recognized medical condition; however, the term has achieved some currency in newspapers, magazines, blogs, and other popular media. "Forgotten baby syndrome" can result in the child being severely injured or dying due to entrapment in a hot car. In general, this is the unintentional behaviour of continuously busy parents who either forget to remove their child from the rear seat of a vehicle or forget to drop them off at an intended destination, often because of a deviation from their automatic habits.

Prevention

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 daylight hours in hot weather; so should remaining in confined spaces (such as automobiles) without air-conditioning or adequate ventilation.

In hot weather, people need to drink plenty of cool liquids 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 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

Person being cooled with water spray

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 of paramount importance 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 actually 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.

Prognosis

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.

Epidemiology

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. An extreme 2003 European heat wave caused tens of thousands of deaths.

External links

• Heat stroke on MedicineNet.com