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Heat-Related Illness

Heat stroke High-yield Verified · Sep 2026

Heat-related illness is a spectrum of conditions caused by heat stress, progressing from minor illness (heat cramps, syncope, edema, rash) through heat exhaustion — water and salt loss with elevated temperature and intact thinking — to heat stroke, a severe elevation in core temperature (typically but not always above 40 °C) with central nervous system dysfunction such as delirium, ataxia, seizures or coma.

A hot patient who is confused has heat stroke until proven otherwise — even if still sweating. The fix is cooling, fast: ice-water immersion if possible, otherwise wetting, fanning and ice packs, with continuous core temperature monitoring and a stop point near 38–39 °C. Acetaminophen will not work. Heat exhaustion — heavy sweating, clammy skin, a fast weak pulse — improves with a cool place, rest and fluids, but vomiting, worsening or symptoms lasting over an hour need help right away.

What’s going wrong in the body

The normal physiology, where it fails, and why the body’s compensation backfires.

01 Heat gain outruns heat loss

"Normally, thermoregulation is an extremely efficient process, with a mere 1 °C change in core temperature for every 25 °C to 30 °C change in ambient temperature." "Thermoreceptors found in the skin, organs, and spinal cord relay information via afferent nerve fibers to the preoptic area of the hypothalamus."

How the body sheds heat. "Heat exchange with the environment occurs through evaporative, convective, conductive, and radiative loss." As air temperature rises, "evaporative dissipation of heat is the primary means by which the body can cool itself." But "evaporative cooling becomes ineffective when environmental humidity exceeds 75%," and radiation, conduction and convection fail "when the ambient temperature exceeds skin temperature."

The cost. The heart must "increase blood flow to shunt heat from the core to the surface while meeting the metabolic demands of exercise." "Apart from environmental conditions and intensity of exercise, dehydration is the most important predisposing factor in heat-related illness." "Temperature and heart rate increase in direct proportion to the level of dehydration" (CDC Yellow Book).

In heat, the body relies on skin blood flow and sweat evaporation; humidity blocks evaporation, sweating drains water and salt, and dehydration drives the progression from heat exhaustion to heat stroke.

02 The spectrum — exhaustion versus stroke

"Heat-related illness is a spectrum of conditions progressing from heat exhaustion and heat injury to life-threatening heat stroke." [HE] "Heat exhaustion is the body's response to an excessive loss of water and salt, usually through excessive sweating" (NIOSH). StatPearls: temperature "is not usually elevated at or above 40.5°C [105°F]." Yellow Book: "Mental changes (e.g., irritability, confusion, irrational behavior) might be present in heat exhaustion, but major neurologic signs (e.g., seizures, coma) indicate heat stroke or profound hyponatremia."

[HS] "Heat stroke is a clinical constellation of symptoms that includes a severe elevation in body temperature, typically but not always greater than 40°C. Central nervous system dysfunction, including ataxia, delirium, or seizures, must also occur." Thresholds vary by source — the Yellow Book's field diagnosis pairs a very high body temperature with "marked alteration of mental status"; CDC's flyer lists "High body temperature (103°F or higher)." "Heat stroke is the only form of heat-related illness in which the mechanisms for thermal homeostasis have failed."

Two forms, and sweating. "Classic heat stroke typically affects older adults with chronic medical conditions, whereas exertional heat stroke affects otherwise healthy individuals who engage in strenuous exercise in hot or humid weather." Classic heat stroke often shows hot, dry skin, but "anhidrosis is uncommon in exertional heat stroke, and prolonged sweating may continue after exercise has stopped."

Mental status separates heat stroke (911, cool immediately) from heat exhaustion (cool, rest, fluids — help right away if vomiting, worsening or lasting over an hour); confusion with a normal temperature after heavy drinking suggests hyponatremia.

03 Heat stroke injures every organ

"Uncontrolled hyperthermia and circulatory collapse cause organ damage to the brain, kidneys, liver, and heart. Damage is related to duration and peak elevation of body temperature" (Yellow Book).

Muscle and potassium. "Rhabdo causes the rapid breakdown, rupture, and death of muscle. When muscle tissue dies, electrolytes and large proteins are released into the bloodstream. This can cause irregular heart rhythms, seizures, and damage to the kidneys" (NIOSH). "Hyperkalemia has been associated with heat stroke and may result from potassium release during muscle breakdown." "Rhabdomyolysis is more common in exertional heat stroke than in classic heat stroke."

Clotting. "Heat-induced endothelial damage is believed to promote platelet aggregation and microvascular thrombosis, resulting in consumptive coagulopathy and paradoxical bleeding when platelet consumption exceeds platelet production." Heat stroke ranges from coagulation activation "to fatal hemorrhage or disseminated intravascular coagulation."

Why speed matters. "Mortality correlates with the degree of body temperature elevation, the time before cooling begins, and the number of organ systems affected." "expedited rapid cooling is the most effective intervention for reducing mortality associated with heat stroke."

Heat stroke damages brain, muscle, kidneys, liver, lungs and the clotting system; damage scales with how high and how long the temperature stays up, so rapid cooling is the key treatment.

Causes & risk factors

Modifiable factors are teaching targets — the patient can act on them.

Hot, humid weather; heat waves — "Heatwave (greater-than-or-equal to three days of temperature more than 32.2°C (90.0°F))" Strenuous exertion — athletes, outdoor and indoor workers, protective equipment modifiable Age — infants and children (immature thermoregulation, higher surface area to mass) and adults over 65 Dehydration, alcohol, obesity, stimulant drugs, lack of acclimatization modifiable Chronic illness — cardiovascular disease, diabetes, renal disease, mental health conditions; social isolation or no access to cooling Medications — diuretics, anticholinergics, antipsychotics, beta-blockers, stimulants, ACE inhibitors/ARBs with a diuretic, lithium (CDC) modifiable

Signs & symptoms

Each finding tied to the mechanism that produces it — and the triage it calls for.

[HS] Confusion, slurred speech, seizures, loss of consciousness, very high temperature Report immediately
Why: CNS dysfunction marks heat stroke. NIOSH: "Call 911 for emergency medical care." CDC flyer: "Call 911 right away-heat stroke is a" medical emergency.
[HS] Hot, red skin — dry OR damp Report immediately
Why: CDC lists "Hot, red, dry, or damp skin"; in exertional heat stroke "prolonged sweating may continue after exercise has stopped." Sweating does not rule it out.
[HE] Heavy sweating; cold, pale, clammy skin; fast, weak pulse; nausea; dizziness; weakness; fainting Hold & notify
Why: Water and salt loss with a strained circulation. NIOSH: take the worker "to a clinic or emergency room for medical evaluation and treatment."
[HE] Vomiting, worsening symptoms, or symptoms lasting longer than 1 hour Report immediately
Why: CDC: "Get medical help right away if:" "You are throwing up," "Your symptoms get worse," "Your symptoms last longer than 1 hour." Heat exhaustion "can progress to life-threatening heatstroke."
[RHABDO] Muscle pain with dark (tea- or cola-colored) urine after heat or exertion Report immediately
Why: Muscle breakdown releasing myoglobin and potassium. NIOSH: "Seek immediate care at the nearest medical facility."
[EAH] Confusion with a normal temperature after drinking large amounts of water Report immediately
Why: "altered mental status in a patient with normal body temperature and a history of taking in large volumes of water suggests hyponatremia." "Treating clinicians should restrict fluid if hyponatremia is suspected."
[MINOR] Heat cramps lasting more than 1 hour, or in someone with heart problems or on a low-sodium diet Hold & notify
Why: NIOSH: "Get medical help if the worker:" "Has heart problems," "Is on a low sodium diet," or "Has cramps that do not subside within 1 hour."
[MINOR] Painful cramps in the calves, thighs or abdomen that ease with rest and fluids Expected
Why: Salt and water depletion — "Low salt levels in muscles cause painful cramps." Stop activity and rehydrate.
[MINOR] Swelling of hands and feet; heat rash Expected
Why: Heat edema from "vasodilation and gravity-dependent pooling of fluids"; heat rash from "excessive sweating during hot, humid weather." Self-limited.

Diagnostics

Test In this disorder Normal
Core (rectal) temperature "a core temperature should be obtained with rectal thermometry if clinically possible." During cooling, core temperature "should be continuously monitored with a rectal or esophageal probe." Heat stroke: typically > 40 °C (StatPearls); mental status is the discriminator —
Creatine kinase, urine myoglobin "Creatinine kinase levels to evaluate for skeletal muscle injury and rhabdomyolysis"; rhabdomyolysis is "more common in exertional heat stroke." Elevated with rhabdomyolysis —
Electrolytes, glucose, kidney and liver tests "patients with heat illness frequently have hypoglycemia and may require carbohydrate replacement." "In classic heat stroke, elevated aspartate aminotransferase and alanine aminotransferase levels are the most commonly reported laboratory abnormalities." Hyperkalemia, hypocalcemia, hypoglycemia, ↑ creatinine, ↑ AST/ALT —
CBC, PT, aPTT Heat stroke labs include "a complete blood count, comprehensive metabolic panel, prothrombin time, activated partial thromboplastin time, blood gases, serum creatine phosphokinase level, and urine myoglobin measurement." Coagulopathy / DIC in heat stroke —
Blood gases "In classic heat stroke, respiratory alkalosis predominates, whereas exertional heat stroke may also involve concomitant lactic acidosis." Classic: respiratory alkalosis; exertional: may add lactic acidosis —
ECG Continuous cardiac monitoring during cooling "is recommended when available." ST depression, QT prolongation, T-wave changes possible —

Complications

Black-box warning — most severe: ■ [HS] Death and permanent disability Report immediately
NIOSH: "Heat stroke can cause permanent disability or death if the person does not receive emergency treatment." StatPearls: "The mortality rate for exertional heat stroke is relatively low, ranging from 3% to 5%, compared with 10% to 65% for classic heat stroke"; "immediate rapid cooling was associated with no fatalities among young patients with exertional heat stroke."
Warning: Multi-organ failure Report immediately
"Complications of heat stroke include acute respiratory distress syndrome, disseminated intravascular coagulation, acute kidney injury, hepatic injury, hypoglycemia, rhabdomyolysis, and seizures." "many complications occur in the first 24–48 hours, including liver or kidney damage and abnormal bleeding" (Yellow Book).
Caution: Overcooling and ice injury Hold & notify
"Core temperatures below normal (36 °C) put patients at risk for hypothermia-related complications, including arrhythmias and coagulopathy." "prolonged exposure to ice can cause tissue damage. Covering ice packs with a towel or sheet and regularly repositioning them mitigates this risk."
"shivering can impede effective cooling" — benzodiazepines may be used for shivering or agitation.
Caution: Slow recovery
"even reversible complications following heat stroke may take longer than 7 weeks to resolve." After exertional heat stroke, "the patient should abstain from exercise for at least 7 days," with follow-up at 1 week.
Caution: Sodium extremes
"Severe hypernatremic dehydration may lead to hemorrhage, cerebral edema, and permanent neurologic injury." Hyponatremia can follow "excessive hypotonic fluid replacement, as seen in marathon runners." "rapid correction of sodium abnormalities should be avoided."

Medications for this condition

Why each class is prescribed here — every card links to its full pharmacology page.

Electrolyte & Fluid Replacement First-line High-alert
Renal

Rehydration — without overdoing it. Heat exhaustion and cramps: "oral rehydration with water or an electrolyte-containing drink can commence on-site"; the Yellow Book adds fluids "containing glucose and salt." Heat stroke: "Adequate rehydration is essential, although rapid correction of sodium abnormalities should be avoided"; many need intensive care to replace losses. "Care should be taken not to overhydrate patients," especially with reduced cardiac function. Salt: NIOSH says "Avoid salt tablets" for heat cramps; the Yellow Book notes "Salt tablets swallowed whole can cause gastrointestinal irritation and vomiting." Not used: antipyretics — "Antipyretics have no role in the treatment of heat stroke and may cause hepatic toxicity"; dantrolene — "does not improve outcomes"; diuretics for heat edema — "There is no role for diuretic medications for heat edema."

Beyond medications

  • Heat stroke — cool immediately. "Activate emergency medical services or plan for urgent evacuation, but do not delay cooling measures." "Ice-water immersion has been shown to be the most effective method" (about 0.13 °C per minute vs 0.05 °C per minute for evaporative cooling). If immersion is impractical, "Evaporative cooling using mist and fans is the next most efficient method"; ice packs to groin, axillae and neck are "less effective."
  • Stop point (by source). StatPearls Heat Stroke: stop active cooling "when the temperature reaches 38 °C to 39 °C." StatPearls Cooling Techniques: reduce "core temperature below 39 °C, with the ultimate goal of achieving the normal range of 36 °C to 38 °C." "The only absolute contraindication to cooling is a normal or low body temperature."
  • Heat exhaustion first aid — CDC: move to a cool place, loosen clothes, put on cool wet cloths or take a cool bath, and sip water. Yellow Book: "supine rest in the shade or other cool place" and oral fluids; recovery within hours.
  • Minor illness — cramps: stop activity, rehydrate, stretch; syncope: "Supine positioning with leg elevation above the level of the heart"; edema: elevation and compression; rash: keep dry, powder, no ointments.
  • Prevention — "Prevention is the definitive treatment for heat stroke." Shade, breaks, cooler times of day, air conditioning (dial 2-1-1 for a cooling location); "Use fans, but only if indoor temperatures are less than 90°F"; lightweight, loose, light-colored clothing; never leave children in vehicles; check on older and isolated neighbors.
  • Hydration balance — "Check your urine color"; but "forcing a person who is not thirsty to drink water increases the risk of hyponatremia."
  • Workers (NIOSH) — acclimatize over 7 to 14 days (for new workers: no more than 20% of the usual time in the heat on day 1, then no more than a 20% increase each day); buddy system; cool water nearby; report symptoms immediately. StatPearls, citing WMS: the wet-bulb globe temperature index is "an excellent assessment of the environmental risk."

Nursing considerations

The RN-specific layer — each action paired with the reason it matters.

Assessment
In any hot, unwell patient, check mental status first — confusion, slurred speech, seizure or collapse means heat stroke until proven otherwise.
Why: CNS dysfunction "distinguishes heat stroke from heat injury"; sweating does not exclude it.
Obtain a rectal (core) temperature; during cooling, monitor core temperature continuously with cardiac monitoring.
Why: A rectal temperature "is the most reliable way"; the team must stop cooling at the target to avoid overcooling.
Monitor urine color and output, CK, potassium, glucose, creatinine and coagulation results.
Why: Rhabdomyolysis, hyperkalemia, hypoglycemia, kidney injury and DIC are heat-stroke complications.
Review medications — diuretics, beta-blockers, anticholinergics, antipsychotics, stimulants, lithium.
Why: "Medication reconciliation is crucial when evaluating patients with suspected classic heat stroke."
Interventions
For heat stroke: call 911 / rapid response, secure the airway, and start cooling at once — cold-water immersion if possible, otherwise wet skin plus fanning and ice packs. Stay with the patient; give nothing by mouth.
Why: "do not delay cooling measures"; CDC: "Do not give the person anything to" drink.
During immersion, attend and hold the person in the water; cover ice packs and reposition them; watch for shivering.
Why: Yellow Book: "Always attend and hold the person while in the water." Ice can injure skin; shivering impedes cooling.
Communicate clearly to stop cooling at the ordered target (about 38–39 °C).
Why: "clear communication is required to discontinue cooling when the core temperature reaches 38 °C to 39 °C."
Question any order for acetaminophen or other antipyretics for heat stroke.
Why: Antipyretics "may exacerbate coagulopathy and contribute to organ dysfunction."
Heat exhaustion: move to a cool place, loosen clothing, cool compresses, frequent sips of cool water; escalate for vomiting, worsening or symptoms over 1 hour.
Why: NIOSH and CDC first aid; exhaustion can progress to heat stroke.
Patient teaching
Drink regularly and check urine color, but do not force fluids beyond thirst during long exercise.
Why: The idea "is outdated and dangerous"; over-drinking causes hyponatremia.
Stay in air conditioning or shade in heat; fans only when indoor temperature is below 90°F.
Why: "In temperatures above 90°F, a fan can increase body temperature."
Don't stop or change medicines without talking to the provider; don't leave medicines, insulin or inhalers in a hot car.
Why: CDC: inhalers "can burst," EpiPens "may malfunction," insulin "may become less effective" in heat.
Never leave children in vehicles; check on older adults and people living alone.
Why: "Older adults should be checked frequently, particularly those without access to air conditioning."
After exertional heat stroke, no exercise for at least 7 days and a follow-up visit at 1 week.
Why: StatPearls return-to-activity advice to check for end-organ damage.

How a real nurse thinks

The clinical-judgment loop, worked for a typical presentation — reasoning, not reference.

  1. 1
    Recognize cues

    Confusion and combativeness, rectal temperature 41.3 °C, tachycardia, low blood pressure, collapse during exertion in heat — with ongoing sweating.

  2. 2
    Analyze cues

    High core temperature plus CNS dysfunction is exertional heat stroke. Sweating does not rule it out — anhidrosis is uncommon in the exertional form. Mortality depends on how long the temperature stays high, so cooling cannot wait for transport.

  3. 3
    Prioritize

    Airway and immediate whole-body cooling — ice-water immersion now.

  4. 4
    Generate solutions

    Confirm EMS is coming; immerse him in the ice-water tub with staff holding him; monitor rectal temperature continuously; plan to stop at about 38–39 °C; nothing by mouth; no antipyretics; anticipate labs for CK, potassium, glucose, creatinine and clotting.

  5. 5
    Take action

    He is lowered into the ice-water tub, supported under the arms, with a rectal probe in place. Temperature is read continuously and called out. At 38.9 °C he is removed, dried and placed on his side; EMS transports him with SBAR: exertional heat stroke, initial rectal 41.3 °C, confused, immersion cooling to 38.9 °C.

  6. 6
    Evaluate

    By the end of cooling he is answering questions and oriented. In the ED his CK is elevated and urine is dark; IV fluids continue and kidney function is monitored. He is told not to exercise for at least 7 days and to return for follow-up in 1 week.

Scenario — you’re the nurse

Work each question before revealing the answer. Rationales explain the wrong options too.

High-school cross-country meet · medical tent · 1430

A 17-year-old runner collapses near the finish on a hot, humid afternoon. Teammates carry him to the medical tent. He has no known medical problems.

Neuro — confused, combative, does not know where he is
Skin — hot, flushed and still sweating heavily
Vital signs — rectal T 41.3 °C · HR 148 · BP 96/50 · RR 30
Available — ice-water tub, ice, towels, fans; EMS called
Q1 Select all that apply
Which findings support heat stroke in this runner? Select all that apply.
  1. A. Confusion and combativeness
  2. B. Rectal temperature 41.3 °C
  3. C. Collapse during exertion in heat
  4. D. Heavy sweating proves it is only heat exhaustion
  5. E. Tachycardia
Reveal answer & rationale
Answer: A, B, C, E
Heat stroke is a high core temperature with CNS dysfunction (A, B) after strenuous exertion in heat (C), with tachycardia (E). Sweating does not rule it out: "anhidrosis is uncommon in exertional heat stroke, and prolonged sweating may continue after exercise has stopped" (D is false).
Q2 Multiple choice
EMS is 10 minutes away. What is the nurse's priority action?
  1. A. Wait for EMS so cooling can be done in the hospital
  2. B. Begin ice-water immersion now while monitoring core temperature
  3. C. Give oral fluids and acetaminophen
  4. D. Apply a single ice pack to the forehead
Reveal answer & rationale
Answer: B
Activate EMS "but do not delay cooling measures"; "Ice-water immersion has been shown to be the most effective method" (B). Waiting (A) prolongs hyperthermia; oral fluids and antipyretics are contraindicated (C); a single ice pack (D) is far less effective.
Q3 Multiple choice
An order reads ‘acetaminophen for temperature over 38.5 °C’. What should the nurse do?
  1. A. Give it — it will lower the temperature quickly
  2. B. Give it rectally since he is confused
  3. C. Question the order — antipyretics have no role in heat stroke
  4. D. Give it with ibuprofen for a stronger effect
Reveal answer & rationale
Answer: C
"Antipyretics have no role in the treatment of heat stroke and may cause hepatic toxicity"; they "may exacerbate coagulopathy" (C). Giving it by any route (A, B) or combining it with ibuprofen (D) is inappropriate.
Q4 Multiple choice
When should active cooling be stopped?
  1. A. When core temperature reaches about 38–39 °C, per order
  2. B. When core temperature reaches 35 °C
  3. C. When he stops sweating
  4. D. After exactly 60 minutes regardless of temperature
Reveal answer & rationale
Answer: A
StatPearls: cooling "should be discontinued when the temperature reaches 38 °C to 39 °C" (A). Below 36 °C risks "hypothermia-related complications, including arrhythmias and coagulopathy" (B). Sweating (C) and a fixed time (D) are not targets — core temperature is.
Q5 Select all that apply
A 78-year-old on a diuretic lives alone without air conditioning. Which heat-wave teaching is correct? Select all that apply.
  1. A. Use a fan alone even when it is 95°F indoors
  2. B. Go to an air-conditioned place; dial 2-1-1 to find one
  3. C. Do not stop the diuretic without talking to the provider
  4. D. Arrange for someone to check on you
  5. E. Keep medicines out of a hot car
Reveal answer & rationale
Answer: B, C, D, E
CDC: find air conditioning via 2-1-1 (B); "Remind patients to avoid abruptly stopping any medications without having a plan in place" (C); identify "a point of contact to check on them" (D); don't leave medications in hot places (E). "In temperatures above 90°F, a fan can increase body temperature" (A).

Common questions

What causes heat-related illness?
Common causes and risk factors include hot, humid weather; heat waves — "heatwave (greater-than-or-equal to three days of temperature more than 32.2°c (90.0°f))", strenuous exertion — athletes, outdoor and indoor workers, protective equipment, age — infants and children (immature thermoregulation, higher surface area to mass) and adults over 65, dehydration, alcohol, obesity, stimulant drugs, lack of acclimatization, chronic illness — cardiovascular disease, diabetes, renal disease, mental health conditions; social isolation or no access to cooling, and others.
Why doesn't acetaminophen work for heat stroke?
In heat stroke the body's heat-regulating mechanisms have failed. StatPearls: "Antipyretics have no role in the treatment of heat stroke and may cause hepatic toxicity." Only physical cooling lowers the temperature.
Can someone have heat stroke and still be sweating?
Yes. Hot, dry skin is typical of classic heat stroke, but in exertional heat stroke "prolonged sweating may continue after exercise has stopped." Mental status, not sweating, is the key.
What is the fastest way to cool someone?
"Ice-water immersion reduces core body temperature most rapidly." If that is impractical — for example in some older adults who need cardiac monitoring — mist and fans are next, then ice packs to the groin, axillae and neck.
Is it possible to drink too much water in the heat?
Yes. The Yellow Book warns that forcing fluids "is outdated and dangerous"; "Prevention includes drinking only enough to relieve thirst." Confusion with a normal temperature after heavy drinking suggests hyponatremia.
Which medicines raise heat risk?
CDC names diuretics, anticholinergic agents and some psychotropic medications, and warns that an ACE inhibitor or ARB with a diuretic "may significantly increase risk of harm from heat exposure."

Sources

Reviewed by Hae Suk Lee, RN

Educational summary for nursing students. Scenarios are fictional teaching cases. Always verify against current guidelines and your institution's protocols before acting in practice. Not medical advice.

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