Heat-Related Illnesses lecture 2024,Power point
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Definition, importance, epidemiology, pathophysiology, risk factors, fever vs hyperthermia
Heat-Related Illnesses lecture 2024,Power point
- 2. Heat-related illnesses include a spectrum of disorders ranging from heat syncope, muscle cramps, and heat exhaustion to medical emergencies such as heatstroke. The core body temperature is normally maintained within a very narrow range. Although significant levels of hypothermia are tolerated , multiorgan dysfunction occurs rapidly at temperatures >41°–43°C. In contrast to heatstroke, the far more common sign of fever reflects intact thermoregulation.
- 7. Heat Production • Humans are essentially biochemical furnaces that burn food to fuel with a complex array of metabolic functions. Water and carbon dioxide are produced and eliminated in large quantities, as well as urea, sulfates, phosphates, and other chemical byproducts. These reactions are exothermic and combine to produce a basal metabolic rate that amounts to approximately 100 kCal/h for a 70- kg person. In the absence of cooling mechanisms, this baseline metabolic activity would result in a 1.1°C (2°F) hourly rise in body temperature. Heat production can be increased 20- fold by strenuous exertion. Rectal temperatures as high as 42°C (107.6°F) have been recorded in trained marathon runners, without ill effects. Metabolic factors (hyperthyroidism and sympathomimetic drug ingestion) can dramatically increase heat production. Environmental heat not only adds to the heat load but also interferes with its dissipation.
- 8. THERMOREGULATION • Humans are capable of significant heat generation. Strenuous exercise can increase heat generation twentyfold. The heat load from metabolic heat production and environmental heat absorption is balanced by a variety of heat dissipation mechanisms. These central integrative dissipation pathways are orchestrated by the central thermostat, which is located in the preoptic nucleus of the anterior hypothalamus. Efferent signals sent via the autonomic nervous system trigger cutaneous vasodilation and diaphoresis to facilitate heat loss.
- 11. Normally, the body dissipates heat into the environment via four mechanisms: • The evaporation of skin moisture : is the single most efficient mechanism of heat loss but becomes progressively ineffective as the relative humidity rises to >70%. • The radiation of infrared electromagnetic energy: directly into the surrounding environment occurs continuously. (Conversely, radiation is a major source of heat gain in hot climates.) • Conduction—the direct transfer of heat to a cooler object • convection—the loss of heat to air currents; become ineffective when the environmental temperature exceeds the skin temperature.
- 15. For an accurate heat illness diagnosis: • information about living conditions, occupation, access to water, strenuous physical activity, acclimatization, and current environmental temperatures need to be ascertained. • Heat illness is often associated with military exercises, athletic events, occupation, and recreational activities. A recognition of the microclimates conducive to heat illness including military tanks, tents in the sun, engine rooms, mines, hot tubs, saunas, and automobile interiors, is also important. In the United States, nearly 40 children die each year from hyperthermia after being left alone in a motor vehicle.
- 16. PREDISPOSING FACTORS: • Heat waves exacerbate the mortality rate, particularly among the elderly and among persons lacking adequate nutrition and access to air-conditioned environments. Secondary vascular events, including cerebrovascular accidents and myocardial infarctions, occur at least 10 times more often in conditions of extreme heat. Exertional heat illness continues to occur when laborers, military personnel, or athletes exercise strenuously in the heat. In addition to the very young and very old, preadolescents and teenagers are at risk since they may use poor judgment when vigorously exercising in high humidity and heat. Other risk factors include obesity, poor conditioning with lack of acclimatization, and mild dehydration. Children are also susceptible to heat stressors because of their higher surface area- to mass ratios. They also have lower sweat rates per gland.
- 17. Fever Versus Hyperthermia • It is diagnostically and therapeutically important to identify patients suffering from a febrile response rather than heat illness. Fever does not cause primary pathologic or physiologic damage to humans and does not require primary emphasis in the therapeutic regimen, which is directed at the underlying disease state. If temperature- related physiologic changes such as febrile seizures and tachycardia compromise • a patient with marginal cardiac reserve, the temperature should be artificially regulated with antipyretics. In contrast, antipyretics are not effective against heat illness and are not recommended to control environmental hyperthermia.
- 19. References: • Harrison principles of internal medicine 21th edition • ROSEN’S Emergency Medicine Concepts and Clinical Practice 10th edition • WHO