{
 "topic": "Heat Exhaustion",
 "slug": "heat-exhaustion",
 "category_id": 15909,
 "summary": "The moderate stage of the pediatric heat-illness continuum between heat cramps and heat stroke, its water- and salt-depletion presentations, and the cooling and rehydration measures that treat it.",
 "written_by": "claude-sonnet",
 "references": [
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 ],
 "short": [
  {
   "title": "In short",
   "content": "- Heat illness is a continuum from heat cramps (mildest) through heat exhaustion (moderate) to heat stroke (life-threatening); it is a leading cause of death in US high school athletes, and stages often progress if early signs are not addressed.\n- Heat exhaustion is a moderate illness with core temperature roughly 37.7-40\u00b0C (100-104\u00b0F), presenting with weakness, fatigue, headache, nausea, vomiting, dizziness, orthostasis, piloerection, and possibly syncope, with only mild or absent CNS dysfunction (unlike heat stroke).\n- Two mechanisms produce heat exhaustion: sustained heat plus dehydration (water depletion \u2014 faintness, extreme tiredness, headache, fever, intense thirst, nausea, vomiting, hyperventilation, paresthesias), and predominant salt depletion (from replacing water losses without adequate electrolytes \u2014 profound weakness/fatigue, frontal headache, anorexia, nausea, vomiting, diarrhea, severe muscle cramps, tachycardia, orthostatic hypotension, with hyponatremia, hemoconcentration, and low urine sodium).\n- Children with cystic fibrosis are at particular risk of salt depletion because their sweat sodium losses do not respond normally to acclimatization or aldosterone stimulation.\n- Children are more heat-vulnerable than adults: a higher surface-area-to-mass ratio, greater heat production per kilogram during activity, a lower sweat rate with a higher sweating threshold temperature, longer acclimatization time (typically 8-12 near-consecutive days of 30-45 minute exposures), and a blunted thirst response that can lead to under-drinking during exercise in hot, humid conditions.\n- Other risk factors: chronic disease (diabetes, obesity, cystic fibrosis), medications (anticholinergics, stimulants, opioids, phenothiazines), reduced ability to seek protection or communicate needs (infants, children with physical disabilities), recent illness with fluid loss (especially gastroenteritis), and sickle cell trait.\n- Modifiable risk factors specific to sports/exertional settings: poor hydration, undue exertion, inadequate recovery between exercise bouts or same-day competitions, and clothing/uniforms/protective equipment that impair heat dissipation \u2014 making exertional heat illness usually preventable with preparation and monitoring.\n- Treatment of heat exhaustion: stop the activity, move to a cool environment, remove excess clothing, cool with fans and ice packs/ice water over the groin and axillae, and rehydrate orally with electrolyte-containing fluids (or IV fluids if oral intake is not tolerated); monitor rectal temperature and discontinue active cooling once temperature falls below about 38.9\u00b0C (102\u00b0F) or shivering occurs.\n- Full recovery is the rule for heat cramps and heat exhaustion (in contrast to heat stroke, which risks organ damage from volume depletion, rhabdomyolysis, and direct organ injury); watch closely during treatment for progression to heat stroke, and transport to an emergency facility if rapid improvement is not achieved."
  }
 ],
 "long": [
  {
   "title": "Definition",
   "content": "Heat illness spans a spectrum from mild (heat cramps) through moderate (heat exhaustion) to potentially fatal (heat stroke). Heat exhaustion is the moderate stage, defined by a core temperature of roughly 37.7-40\u00b0C (100-104\u00b0F, one source specifies 38.9-40.0\u00b0C/102-104\u00b0F), typically resulting from a combination of sustained heat exposure and dehydration, with only mild or absent central nervous system dysfunction distinguishing it from heat stroke."
  },
  {
   "title": "Epidemiology",
   "content": "Heat illness is among the leading causes of death in US high school athletes. Exertional heat stroke, the most severe endpoint of the continuum, causes more than 9,000 illnesses per year among US high school athletes and remains one of the most common causes of death and disability in this group."
  },
  {
   "title": "Etiology",
   "content": "Children are more vulnerable to heat illness than adults because of a greater surface-area-to-body-mass ratio, greater heat production per kilogram of body weight during activity, a lower sweat rate, and a higher core temperature threshold before sweating begins. Children also take longer to acclimatize to warm, humid environments (typically 8-12 near-consecutive days of 30-45 minute exposures) and have a blunted thirst response compared with adults, which can lead to inadequate fluid intake during exercise in hot conditions. Modifiable risk factors for exertional heat illness in sports include poor hydration status, undue physical exertion, insufficient recovery time between repeated exercise bouts or closely scheduled same-day competitions, and clothing, uniforms, or protective equipment that impairs heat dissipation. Additional risk factors include chronic disease (diabetes mellitus, obesity, cystic fibrosis), certain medications (anticholinergics, stimulants, opioids, phenothiazines), reduced ability to seek protection or communicate needs (as in infants or children with physical disabilities), recent illness with residual fluid loss (particularly gastroenteritis), and sickle cell trait, which increases the risk of complications from strenuous exercise in the heat."
  },
  {
   "title": "Pathophysiology",
   "content": "In hyperthermia, core temperature rises above normal because heat-dissipating homeostatic mechanisms are overwhelmed; contrary to earlier assumptions, children do not actually have less effective thermoregulation, insufficient cardiovascular capacity, or lower exercise tolerance than adults when adequately hydrated. Dehydration results from combined insensible losses (exhaled air, sweat); children sweat at roughly 1 L/hour/m2, and unacclimatized adolescents can lose 1-4 L of fluid, along with several grams of salt, in a single hour of exertion. Heat exhaustion can arise predominantly from water depletion (sustained heat plus inadequate fluid replacement) or predominantly from salt depletion (water losses replaced without adequate electrolyte replacement); children with cystic fibrosis are particularly susceptible to salt depletion because their elevated sweat sodium losses do not respond normally to acclimatization or aldosterone stimulation of the sweat gland."
  },
  {
   "title": "Clinical features",
   "content": "Heat exhaustion presents with weakness, fatigue, headache, nausea, vomiting, dizziness, orthostasis, piloerection, and possibly syncope, with central nervous system dysfunction mild or absent. The water-depletion pattern includes faintness, extreme tiredness, headache, fever, intense thirst, nausea, vomiting, hyperventilation, and paresthesias. The salt-depletion pattern instead features profound weakness and fatigue, frontal headache, anorexia, nausea, vomiting, diarrhea, and severe muscle cramps, with tachycardia and orthostatic hypotension; laboratory findings can include hyponatremia, hemoconcentration, and significantly diminished urine sodium. This contrasts with heat stroke, the most extreme form, defined by a core temperature above 104-105\u00b0F (40-40.5\u00b0C) with signs of central nervous system dysfunction (stupor or coma), tachycardia, hypertension or hypotension, hyperpyrexia (41\u00b0C/105.8\u00b0F or higher), hot skin that may be dry (anhidrosis) or still moist depending on circulatory status, and potentially severe rhabdomyolysis with myoglobinuria and acute kidney injury; sweating often ceases just before heat stroke onset."
  },
  {
   "title": "Differential diagnosis",
   "content": "Heat cramps are the mildest form of heat illness \u2014 exercise-associated muscle cramps without significant systemic symptoms, treated with rest, hydration, salt replenishment, and stretching. Heat stroke is distinguished from heat exhaustion by a higher core temperature and the presence of significant CNS dysfunction; heat stroke can be exertional (in athletes, soldiers, laborers) or nonexertional (in children, most often from being left unattended in a vehicle, where internal temperature rises rapidly above ambient). Malignant hyperthermia, a distinct, rare autosomal-dominant disorder (prevalence about 1:3000, from a ryanodine receptor/RyR1 mutation), causes non-environmental hyperthermia triggered by volatile anesthetic agents or succinylcholine, and should not be confused with environmental heat illness."
  },
  {
   "title": "Treatment",
   "content": "Treatment of heat exhaustion includes moving the child to a cool environment, removing excess clothing, cooling with fans, and applying ice over the groin and axillae (or an ice-water bath/ice packs); oral rehydration with electrolyte-containing fluids is preferred, with intravenous fluids reserved for those unable to tolerate oral intake. Monitor rectal temperature throughout treatment and watch for signs of progression to heat stroke; discontinue active cooling once temperature falls below about 38.9\u00b0C (102\u00b0F) or shivering occurs. If rapid improvement is not achieved, transport to an emergency facility, since heat stroke requires ICU-level care."
  },
  {
   "title": "Complications",
   "content": "Full recovery is the rule for heat cramps and heat exhaustion. This contrasts sharply with heat stroke, where patients are at risk of end-organ damage from volume depletion, rhabdomyolysis, direct renal injury, hepatocellular injury, and disseminated intravascular coagulation \u2014 though even in this critically ill population, some children recover fully with intensive management."
  },
  {
   "title": "Prevention",
   "content": "Because the main risk factors for exertional heat illness \u2014 poor hydration, undue exertion, inadequate recovery between exercise bouts, closely scheduled same-day competitions, and heat-retaining clothing or protective equipment \u2014 are modifiable, exertional heat illness is usually preventable. With appropriate preparation, acclimatization, hydration, salt replenishment (e.g., sports drinks), and monitoring, most healthy children and adolescents can safely participate in outdoor sports across a wide range of warm to hot conditions. A child exhibiting nausea, vomiting, headache, dizziness, or mental status change after heat exposure should be removed from the activity, rehydrated, and evaluated promptly to prevent progression to heat stroke."
  }
 ],
 "clinical": [
  {
   "title": "Recognizing heat exhaustion and separating it from heat stroke",
   "content": "In a child with weakness, fatigue, headache, nausea, vomiting, dizziness, orthostasis, or syncope after heat exposure or exertion, with a core temperature roughly 37.7-40\u00b0C (100-104\u00b0F) and only mild or absent CNS dysfunction, diagnose heat exhaustion. Distinguish the water-depletion pattern (fever, intense thirst, hyperventilation, paresthesias) from the salt-depletion pattern (severe muscle cramps, anorexia, diarrhea, orthostatic hypotension, hyponatremia, hemoconcentration, low urine sodium) \u2014 the latter especially in a child with cystic fibrosis, whose sweat sodium losses do not normalize with acclimatization. Critically, differentiate from heat stroke: a core temperature above 104-105\u00b0F with stupor, coma, seizure, or other significant CNS dysfunction, hot/possibly dry skin, and hemodynamic instability signals heat stroke, a life-threatening emergency requiring immediate aggressive cooling and ICU-level care rather than the measures used for heat exhaustion."
  },
  {
   "title": "Cooling and rehydration",
   "content": "Move the child to a cool environment, remove excess clothing, and cool actively with fans and ice packs or ice water applied over the groin and axillae. Rehydrate orally with electrolyte-containing fluids if tolerated; use IV fluids if oral intake is not possible. Monitor rectal temperature continuously during cooling, stopping active cooling once the temperature falls below about 38.9\u00b0C (102\u00b0F) or the child begins shivering, to avoid overcooling. Watch closely for any sign of CNS dysfunction or hemodynamic instability during treatment, since this would indicate progression to heat stroke and the need for emergency transport and intensive care; reassure families that full recovery is expected for heat exhaustion once appropriately treated. For prevention in returning athletes, address the modifiable risk factors directly: build in acclimatization time, ensure adequate hydration and salt replacement, schedule adequate recovery between exercise bouts, and choose clothing/equipment that allows heat dissipation."
  }
 ]
}