Heat stroke

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

Heat stroke (or sun stroke; also known as heatstroke and/or sunstroke) is a heat illness defined as a body temperature of greater than 40.6 °C (105.1 °F) due to 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 a hemorrhage of blood flow to the brain. Treatment involves rapid physical cooling.

Sign and symptoms[edit]

Heat stroke presents with a hyperthermia of greater than 40.6 °C (105.1 °F) in combination with confusion and a lack of sweating.[1]

Causes[edit]

Substances that inhibit cooling and cause dehydration such as alcohol, caffeine, stimulants, medications, and age-related physiological changes predispose to so-called "classic" heat stroke. Exertional heat stroke can happen in young people without health problems or medications, most often in athletes and military recruits.

Children and pets in cars[edit]

Children, elderly adults, or disabled individuals left alone in a vehicle are at particular risk of succumbing to heat stroke, even with windows partially open. As these groups of individuals may not be able 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, checking the van or bus for stragglers at the end of the trip is essential, complemented by other procedures such as a head count.[2]

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. Non-guide dogs are prohibited from being brought into many establishments, and opening a vehicle window sufficiently may present an escape opportunity or bite hazard. Leaving the pet at home with plenty of water on hot days is recommended instead, or, if a dog must be brought along, tied up outside the destination and provided with a full water bowl.[3]

Between 1998 and 2011, at least 500 children in the United States died from being inside hot cars, and 75% of them were less than 2 years old. When the outside temperature is 70 degrees Fahrenheit (21.1°C), the temperature inside the car can exceed 120 degrees (48.8°C), even when the windows are partially open.[4]

Legal prosecution of parents in this situation varies greatly. In separate incidents, a college professor in California forgot his son in a hot car and a horse trainer in Florida deliberately left his daughter in a hot car. Each resulted in the unintentional death of a child, but the college professor was never prosecuted, while the horse trainer was sentenced to 20 years in prison.[5]

Among all child deaths in hot cars, slightly more than half occur because parents forget that the child is in the car, 18% happen after parents intentionally leave the child in a car without understanding how hot it can get, and 30% happen after the child had climbed into the car to play.[6]

Forgotten baby syndrome[edit]

Forgotten baby syndrome (FBS) is a pseudo-medical term for the danger of adult caregivers forgetting about the presence of a 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.[7][8][9]

Prevention[edit]

The risk of heatstroke can be reduced by observing precautions to avoid overheating and dehydration. Light, loose-fitting clothing will allow perspiration to evaporate and cool the body. Wide-brimmed hats in light colours keep the sun from warming the head and neck and block the powerful radiation from hurting the eyes; vents on a hat will allow perspiration to cool the head. Strenuous exercise should be avoided during daylight hours in hot weather; so should remaining in enclosed spaces (such as automobiles). The temperature inside cars can reach 200°F (c. 93°C) at the right exterior temperature, sunlight, color of vehicle, and type of vehicle.[10] Temperatures that high, without proper cooling, could be dangerous and even fatal, especially with young children and pets.[11] Some preventative measures for vehicles can be some of these new gadgets & apps that have been developed recently.[12]

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 lose heat by evaporation. In such environments, it helps to wear light clothing such as cotton in light colors, that is pervious to sweat but impervious to radiant heat from the sun. This minimizes the gaining of radiant heat, while allowing as much evaporation to occur as the environment will allow. Clothing such as plastic fabrics that are impermeable to sweat and thus do not facilitate heat loss through evaporation can actually contribute to heat stress.[13]

In hot weather people need to drink plenty of liquids to replace fluids lost from sweating. Thirst is not a reliable sign that a person needs fluids.[14] 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 heat stress Quick Card[15] that contains a checklist designed to help prevent heat stress. This list, known as the KBUDWA list, includes:

  • Know signs/symptoms of heat-related illnesses
  • Block out direct sun or other heat sources
  • Use air-conditioning; rest regularly
  • Drink sufficient, cold water and drinks
  • Wear lightweight, light colored, loose-fitting clothes
  • Avoid alcohol, caffeinated drinks, or heavy meals

Treatment[edit]

Patient being cooled with water spray

Treatment involves rapid mechanical cooling along with standard resuscitation measures.[16]

The body temperature must be lowered immediately. The patient 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 may be used: The person is bathed in cool water or a hyperthermia vest can be applied. However, wrapping the patient 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 patient into a bathtub of cool (but not cold) water (immersion method) is a recognized method of cooling. This method requires the effort of 4-5 people and the patient should be monitored carefully during the treatment process. Immersion should be avoided for an unconscious patient, but if there is no alternative, the patient's head must be held above water. Immersion in very cold water is counterproductive, as it causes vasoconstriction in the skin and thereby prevents heat from escaping the body core.

This hypothesis however has been challenged in experimental studies,[17][18] as well as by systematic reviews of the clinical data[19][20] indicating that cutaneous vasoconstriction and shivering thermogenesis do not play a dominant role in the radiant decrease in core body temperature brought on by cold water immersion. This effect can be seen in the effect of (non-therapeutic) 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, 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 heatstroke,[21] showing a lack of endogenous thermogenic response to cold water immersion. Thus, aggressive ice-water immersion remains the gold standard for life-threatening heatstroke.[citation needed]

Hydration is of paramount importance in cooling the patient. In mild cases of concomitant dehydration, this can be achieved by drinking water, or commercial isotonic drinks may be used as a substitute. In exercise- or heat-induced dehydration, electrolyte derangement can result, and may actually result in worsened by excess consumption of water. Hyponatremia can be corrected by intake of hypertonic fluids. Absorption is rapid and complete in most patients, but if the patient is confused, unconscious, or unable to tolerate oral fluid, intravenous rehydration & electrolyte replacement (via a drip) may be necessary.

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

Prognosis[edit]

It is widely believed that heat stroke leads only rarely to permanent deficits and the convalescence is almost complete.[22] American researchers from the University of Chicago Medical Centre followed 58 subjects chosen from more than 3,000 patients with heat-related conditions who were admitted to Chicago area hospitals between July 12 and July 20, 1995 during the 1995 Chicago heat wave. All 58 subjects experienced symptoms of near-fatal heat stroke. Each was interviewed at the time of their discharge from the hospital, with a follow up interview scheduled one year later. Subjects ranged in age from 25 to 95, with the average age of the group being around 67. Nearly half of the patients admitted to Chicago-area ICUs for heat stroke died within a year—21 percent before discharge and another 28 percent after release from the hospital. Many of the survivors suffered permanent loss of independent function; one-third had severe functional impairment at discharge, and none of them had improved after one year.[22] The study also recognized the fact that because of overcrowded conditions in all of the participating hospitals during this crisis, the immediate care – which is critical – was not as comprehensive as it should have been, underlining how important it is to quickly seek medical attention when the first signs occur.

References[edit]

  1. ^ McGugan, Elizabeth A (2001). "Hyperpyrexia in the emergency department". Emergency Medicine Australasia 13 (1): 116–20. doi:10.1046/j.1442-2026.2001.00189.x. PMID 11476402. 
  2. ^ Extreme Heat Guide, Centers for Disease Control and Prevention (CDC)
  3. ^ Pets in Hot Cars
  4. ^ Heat danger: 500th child dies in a hot car, Consumer Reports, June 3, 2011
  5. ^ Court outcomes vary when kids die in hot cars, Associated Press, 2011
  6. ^ More kids die in hot cars, half because parents forget them, USA Today, June 30, 2010
  7. ^ Weingarten, Gene (March 8, 2009). "Forgetting a child in the back seat of a hot, parked car is a horrifying, inexcusable mistake. But is it a crime?". The Washington Post. Retrieved May 2, 2010. 
  8. ^ "The Last Word: Forgotten Baby Syndrome". The Week. March 26, 2009. 
  9. ^ Eisenstein, Paul A. "Death in Hot Cars: Why Can't the Automakers Prevent the Danger?". NBC News. Retrieved 2014-07-13. 
  10. ^ "Summer Car Safety - Heat and Your Vehicle". phoenix.about.com. 2014-05-12. Retrieved 2014-05-19. 
  11. ^ "Avoiding Classic Heat Stroke", Institute for Good Medicine at the Pennsylvania Medical Society
  12. ^ Gibbs Vengrow, Bonnie (July 25, 2014). "Don’t Forget Your Baby in the Car! There’s an App for That". www.parents.com. Retrieved August 12, 2014. 
  13. ^ Guyton, Arthur. (1976) Textbook of Medical Physiology. (5th ed). Philadelphia: W.B. Saunders.[page needed]
  14. ^ Working in Hot Environments. National Institute for Occupational Safety and Health, 1992. NIOSH Publication No. 86-112. Accessed May 21, 2009.
  15. ^ OSHA Quick Card: Protecting Workers from Heat Stress
  16. ^ Tintinalli, Judith (2004). Emergency Medicine: A Comprehensive Study Guide (6th ed.). McGraw-Hill Professional. p. 1188. ISBN 0-07-138875-3. 
  17. ^ Clements, JM; Casa, DJ; Knight, J; McClung, JM; Blake, AS; Meenen, PM; Gilmer, AM; Caldwell, KA (2002). "Ice-Water Immersion and Cold-Water Immersion Provide Similar Cooling Rates in Runners with Exercise-Induced Hyperthermia". Journal of athletic training 37 (2): 146–150. PMC 164337. PMID 12937427. 
  18. ^ Proulx, CI; Ducharme, MB; Kenny, GP (2003). "Effect of water temperature on cooling efficiency during hyperthermia in humans". Journal of Applied Physiology 94 (4): 1317–23. doi:10.1152/japplphysiol.00541.2002 (inactive July 31, 2012). PMID 12626467. 
  19. ^ McDermott, Brendon P.; Casa, Douglas J.; Ganio, Matthew S.; Lopez, Rebecca M.; Yeargin, Susan W.; Armstrong, Lawrence E.; Maresh, Carl M. (2009). "Acute Whole-Body Cooling for Exercise-Induced Hyperthermia: A Systematic Review". Journal of Athletic Training 44 (1): 84–93. doi:10.4085/1062-6050-44.1.84. PMC 2629045. PMID 19180223. 
  20. ^ Gagnon, Daniel; Lemire, Bruno B.; Casa, Douglas J.; Kenny, Glen P. (2010). "Cold-Water Immersion and the Treatment of Hyperthermia: Using 38.6°C as a Safe Rectal Temperature Cooling Limit". Journal of Athletic Training 45 (5): 439–44. doi:10.4085/1062-6050-45.5.439. PMC 2938313. PMID 20831387. 
  21. ^ Hausfater, Pierre (2004). "Dantrolene and heatstroke: A good molecule applied in an unsuitable situation". Critical Care 9 (1): 23–4. doi:10.1186/cc2939. PMC 1065093. PMID 15693976. 
  22. ^ a b "Classic heat stroke during Chicago 1995 heat wave". University of Chicago Medicine. August 1, 1998. Retrieved 2012-07-22. 

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