Heatstroke recognition and cooling

Heatstroke kills through a predictable sequence: core temperature climbs above 104°F (40°C), the central nervous system fails, organ damage begins within minutes, and death follows if cooling is delayed. The 2003 European heatwave killed an estimated 70,000 people — most of them elderly patients who were not cooled fast enough. The evidence is unambiguous: for every minute a heatstroke patient stays hot, organ damage accumulates. Cold water immersion is the most effective field cooling method available. Start it before you call for transport, not after.

Educational use only

This page provides general educational information for emergency preparedness scenarios when professional medical care is unavailable. It is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of a qualified healthcare provider. Use this information at your own risk.

The heat illness spectrum

Heat illness exists on a continuum. Recognizing where a patient sits on that spectrum determines the urgency of your response.

Condition	Core temp	Mental status	Skin
Heat cramps	Normal	Normal	Normal
Heat syncope	Normal or slightly elevated	Brief faint, recovers quickly	Pale, cool
Heat exhaustion	Up to 104°F (40°C)	Normal or mildly impaired	Pale, clammy
Heatstroke	Above 104°F (40°C)	Altered, confused, combative, unconscious	Hot (dry or wet)

Condition	Sweating	Urgency
Heat cramps	Heavy	Low — stretch, hydrate, rest
Heat syncope	Yes	Moderate — rest, cool environment, oral fluids
Heat exhaustion	Heavy	High — active cooling, oral fluids, monitor
Heatstroke	Variable	Emergency — immediate aggressive cooling

Heat cramps

Heat cramps are painful, involuntary muscle spasms occurring during or after intense exercise in the heat. The mechanism is sodium depletion from prolonged sweating combined with drinking plain water, which dilutes the remaining sodium further. Affected muscles are usually the calves, hamstrings, or abdomen.

Treatment: Move to a cool area. Stretch and massage the cramping muscle. Give oral electrolyte solution — not plain water alone. If cramps recur despite hydration, the person is likely sodium-depleted; add 1/4 teaspoon (1.5 g) of salt to their next 1-liter (34 oz) fluid dose.

Heat exhaustion

Heat exhaustion is a volume and electrolyte depletion state with core temperatures typically below 104°F (40°C) and intact or near-intact mental status. The patient knows where they are and who you are, even if slow or dizzy.

Hallmark signs: heavy sweating, weakness, nausea, headache, pallor, cool clammy skin, fast weak pulse.

Treatment: Move to shade or air conditioning. Remove excess clothing. Lay the patient down with legs elevated if dizzy. Give cool oral electrolyte solution — 500 mL (17 oz) in the first 30 minutes if tolerated.

Apply cool wet cloths to the skin. Monitor carefully — heat exhaustion can convert to heatstroke within minutes if cooling is inadequate.

Heat exhaustion can escalate without warning

A patient who is alert and oriented with heat exhaustion can deteriorate to heatstroke in minutes — particularly in exertional cases where muscle heat continues generating after activity stops. Do not leave a heat exhaustion patient unsupervised. Check mental status every 5 minutes for the first 30 minutes.

Heatstroke — the emergency

Heatstroke is defined by two criteria, both required:

Core temperature above 104°F (40°C)
Central nervous system dysfunction — any of: confusion, combativeness, altered speech, loss of coordination, seizure, or unconsciousness

If mental status is abnormal in hot conditions and you cannot measure temperature, treat as heatstroke. Do not wait for thermometer confirmation.

Exertional vs classic heatstroke

Knowing the type refines your assessment and helps you anticipate complications.

Feature	Exertional heatstroke (EHS)	Classic heatstroke (CHS)
Who	Young, fit, physically active — soldiers, athletes, laborers	Elderly, sedentary, chronically ill; infants in hot vehicles
Onset	Rapid — hours of intense exertion in heat	Slow — days of heat exposure without adequate cooling
Sweating	Often still sweating at presentation	Classically dry skin — sweat glands exhausted
Core temp	Often very high (106–108°F / 41–42°C)	Usually 104–106°F (40–41°C)
Rhabdomyolysis	Highly likely — severe muscle breakdown	Less common
DIC / bleeding	More common, more severe	Less common
Lactic acidosis	Common from anaerobic exertion	Less prominent
Setting	Military training, marathons, construction, agricultural work	Heat waves, nursing homes, hot cars

The key field pitfall with EHS: the patient may still be sweating. Classic teaching says heatstroke skin is hot and dry — this is true for CHS but not for EHS. A sweating athlete who is confused during a race has heatstroke. Do not be reassured by the sweat.

Core temperature measurement

Rectal temperature is the gold standard for heatstroke assessment. It most accurately reflects true core temperature, unlike oral, axillary, or forehead measurements which underestimate core temp during hyperthermia.

Procedure for rectal temperature:

Position the patient on their side (lateral decubitus) or supine with knees bent.
Lubricate the probe tip with petroleum jelly or similar.
Insert the probe approximately 4 inches (10 cm) past the anal sphincter.
Hold in place for at least 30 seconds for a stable reading on a standard probe; many digital probes signal when stable.
Read and document temperature, time, and any cooling interventions since.

Tympanic (ear) temperature is an acceptable field alternative when rectal measurement is impractical. Use a well-calibrated tympanic thermometer, straighten the ear canal by pulling the pinna upward and backward (in adults), and seal the probe tip in the canal before reading. Tympanic temperatures typically run 0.5–1°F (0.3–0.6°C) lower than rectal. If the tympanic reading is above 103°F (39.4°C) and the patient is altered, treat as heatstroke.

Do not rely on oral, temporal artery, or axillary temperatures for heatstroke management — all significantly underestimate core temperature during hyperthermia.

Cooling procedures

Time to cooling is the single most important variable in heatstroke survival. The target is to reach a rectal temperature of 102°F (38.9°C) within 30 minutes of diagnosis. Research on exertional heatstroke shows that patients cooled to this target within 30 minutes have a mortality rate near zero; those who take longer accumulate irreversible organ damage.

Cold water immersion — first-line treatment

Cold water immersion (CWI) is the gold standard for cooling exertional heatstroke and is the fastest cooling method available without hospital equipment. Cooling rate with CWI: approximately 0.22°C (0.4°F) per minute in a field setting — sufficient to reach the target within 20–30 minutes from a core temp of 40°C.

Remove all clothing and equipment from the patient.
Prepare an immersion container — a stock tank, inflatable pool, large tub, or improvised tarp basin. If none is available, proceed to evaporative cooling immediately (see below).
Fill with cold water. Ice added to the water improves cooling rate. Water temperature range: 35–59°F (2–15°C). Ice water at approximately 35°F (2°C) achieves the fastest cooling rates.
Lower the patient into the water with assistance — support the head and airway above the water surface at all times. The water level should reach the neck.
Monitor airway and mental status continuously — altered patients do not protect their own airway.
Take rectal temperature every 5 minutes while immersed.
Remove the patient from immersion when rectal temperature reaches 102°F (38.9°C). Do not wait until the patient appears to feel better — the goal is 102°F, not normality. Continued immersion below 102°F risks overcooling.
Dry the patient and place in a cool shaded environment.

Field note

A body bag half-filled with ice and water, zippered to neck level with the patient inside, is a documented effective CWI method when no tub is available. Military medical units have used this protocol in austere environments. If you are operating in heat-risk environments, pre-positioning a stock tank or large rigid container at a cool site is worth the logistics investment. Improvising cooling containers after a heatstroke occurs delays treatment by critical minutes.

Evaporative cooling — when CWI is not available

Evaporative cooling is the second-line method. It is less effective than CWI but significantly better than passive cooling alone. Cooling rate: approximately 0.10–0.15°C (0.18–0.27°F) per minute under good conditions.

Remove all clothing and equipment from the patient.
Wet the entire skin surface continuously with cool water — use spray bottles, wet sponges, or wet cloth sheets applied and reapplied. Do not use ice water directly on skin without immersion — skin vasoconstriction from ice water reduces the cooling surface when applied topically.
Fan the patient aggressively — a standard electric fan at close range, or manual fanning with any flat object. Fanning accelerates evaporation.
Simultaneously apply ice packs to high-flow vascular areas: bilateral neck, armpits (axillae), and groin (femoral vessels). Wrap ice packs in thin cloth — do not apply bare ice directly to skin for extended periods.
Take rectal temperature every 5 minutes.
Maintain until rectal temperature reaches 102°F (38.9°C).

Cooling rate and monitoring

Target cooling rate: minimum 0.15°C (0.27°F) per minute. If temperature is not dropping at this rate with CWI or evaporative cooling, increase ice, increase fanning, or both.

Do not interrupt cooling to prepare for transport. Transport should be arranged while cooling is in progress — the patient goes in the ambulance or vehicle with cooling continuing, not cooling paused while they are loaded.

Endpoint of cooling: 102°F (38.9°C) rectal temperature. After this point, the patient's own thermoregulation may continue reducing temperature further (the fever set point has been disrupted by the event). Continue monitoring every 10 minutes after cooling stops for at least 60 minutes to catch rebound hyperthermia.

Fluid resuscitation

Heatstroke patients are typically volume depleted from sweating, and initial fluid resuscitation supports renal perfusion and reduces rhabdomyolysis complications.

Conscious patient — oral route

If the patient is conscious, alert enough to swallow safely (no altered mental status preventing swallowing), and not vomiting:
Give 200–300 mL (7–10 oz) of cool electrolyte solution every 15 minutes.
Use commercial oral rehydration solution, sports drink diluted to half-strength with water, or homemade ORS (see dehydration for the WHO formula).
Do not give plain water as the sole replacement — electrolyte-free fluid compounds sodium dilution.
Continue oral fluids as tolerated until urine is light yellow.

Altered patient — IV/fluid access

For any patient with altered mental status, vomiting, or reduced level of consciousness:

Do not give oral fluids — aspiration risk is real.
Establish IV access if trained and equipped. Normal saline (0.9% NaCl) at 1–2 liters over the first hour is a reasonable starting point.
Monitor for urine output — a minimum of 0.5 mL/kg/hr (about 30–40 mL/hr in an average adult) indicates adequate renal perfusion.
If urine is very dark (cola-colored), increase IV fluid rate — this indicates myoglobinuria from rhabdomyolysis and the kidneys need flushing.

Complications to recognize

Heatstroke is not over when the temperature normalizes. The cascade of organ injury triggered by hyperthermia continues unfolding over hours to days. Knowing what to watch for allows you to recognize deterioration and escalate before systems fail completely.

Rhabdomyolysis

Rhabdomyolysis — breakdown of skeletal muscle releasing myoglobin into the bloodstream — is nearly universal in severe exertional heatstroke. Myoglobin is directly toxic to kidney tubules and can cause acute kidney failure.

Recognition signs: - Urine that is cola-colored, dark brown, or red (myoglobinuria) — appears within hours of the event - Severe muscle pain out of proportion to the activity level - Muscle swelling and weakness persisting after temperature normalizes - Reduced urine output or no urine despite adequate fluid intake

Field response: push fluids aggressively to flush the kidneys. Target urine that lightens toward yellow. IV fluids at 200–250 mL/hr if available. Hospital transfer is required for confirmed rhabdomyolysis — creatine kinase levels and renal function must be measured and managed.

Disseminated intravascular coagulation (DIC)

DIC is a life-threatening clotting disorder triggered by widespread endothelial damage from extreme hyperthermia. The clotting cascade activates throughout the body simultaneously, consuming clotting factors and platelets until they are depleted — creating a paradox where the patient clots and bleeds at the same time.

Recognition signs (appearing 12–48 hours after the event): - Spontaneous bleeding from IV line sites, venipuncture sites, mucous membranes, gums - Petechiae (small red pinpoint spots) and purpura (larger bruise-like patches) spreading across the skin - Blood in urine or stool - Oozing from any wounds that were previously controlled

Field response: There is no field treatment for DIC. Recognize it, protect IV sites from further manipulation, and transport with urgency. DIC in heatstroke carries significant mortality and requires hospital-level coagulation support.

Hepatic failure

Heatstroke causes direct thermal injury to liver cells. Hepatic damage typically becomes apparent 24–72 hours after the acute event.

Recognition signs: - Jaundice (yellow tint to skin and whites of the eyes) appearing 1–3 days after the event - Right upper abdominal pain or tenderness - Nausea, vomiting, and mental status changes in a previously improving patient - Dark brown urine (bilirubin) in the absence of cola-colored myoglobinuria

Any patient who develops jaundice after a heatstroke event requires urgent hospital evaluation. Liver enzyme levels (AST, ALT) will be severely elevated and must be monitored.

Seizures

Seizures during or immediately after heatstroke are a sign of severe CNS involvement. During a seizure: 1. Move the patient to a safe position — on their side if possible. 2. Protect the airway — do not put anything in the mouth. 3. Do not restrain convulsive movements — guide limbs away from hazards. 4. Continue cooling if still above 102°F (38.9°C) rectal temp — hyperthermia drives seizures. 5. Time the seizure. A seizure lasting more than 5 minutes, or two seizures without return to baseline consciousness, requires emergency transport.

Special populations

Children

Children have a higher ratio of body surface area to weight and generate more heat per kilogram during exercise than adults. Children also have a slower sweat rate and less efficient thermoregulation. For infants left in hot vehicles — where car interior temperatures can exceed 130°F (54°C) within 30 minutes on a 90°F (32°C) day — heatstroke develops in minutes, not hours.

Children should be cooled by the same methods as adults. CWI is safe and appropriate. The cooling temperature endpoint remains 102°F (38.9°C) rectal.

Elderly

Classic heatstroke in the elderly is a slow-developing condition driven by: impaired thirst sensation (elderly people do not feel thirst reliably), reduced sweating capacity, multiple medications that impair thermoregulation (diuretics, anticholinergics, beta-blockers, antipsychotics), and social isolation in hot living spaces without air conditioning.

In a heat wave, check on elderly neighbors daily. Look for confusion, hot dry skin, and reduced responsiveness. Act immediately.

Athletes and military

Exertional heatstroke in trained athletes can occur even when ambient temperature is moderate — internal heat production from intense exertion can exceed the cooling capacity of sweating alone. Pre-event cooling (ice vest, cold wet towels), work-rest cycles based on Wet Bulb Globe Temperature (WBGT), and enforcing rest in heat index conditions above 103°F (39.4°C) effective temperature are the primary prevention measures.

Prevention protocols

Prevention is not optional in high-risk operations. These are evidence-based measures, not suggestions.

Acclimatization: Physiological adaptation to heat takes 7–14 days of progressive heat exposure. Do not deploy people to full-intensity hot work on day one. A graduated schedule over two weeks substantially reduces heatstroke incidence.
Hydration schedule: Do not rely on thirst. Enforce hydration breaks every 15–20 minutes during work in heat. Target: 500–750 mL (17–25 oz) per hour in moderate heat, up to 1 liter (34 oz) per hour in extreme heat, not exceeding 1.5 liters per hour (overdrinking causes hyponatremia — see dehydration).
Work-rest cycles: At WBGT above 82°F (28°C), implement 1:1 work-rest ratios. Above 88°F (31°C) WBGT, heavy labor should be suspended or heavily restricted.
Buddy system: Altered mental status is not always self-reported — the affected person often does not realize they are confused. Assign partners to watch for early signs (personality change, confusion, stumbling, stopping mid-task) and report immediately.
Pre-positioned cooling: In operations where heatstroke is a known risk (military training, marathons, outdoor festivals), pre-stage cold water immersion capability before the event starts.

Heatstroke response checklist

Heatstroke prevention and effective dehydration management are inseparable — a dehydrated person has impaired thermoregulation, lower sweat rate, and significantly higher risk of heat illness. Review dehydration for the ORS formula and fluid replacement protocols used when oral intake fails. For shelter planning in extreme heat — including passive cooling design and shade structures — see the shelter foundation and the heat-wave threat overview.