Scenario: An EMS crew is dispatched to a local half-marathon for a 29-year-old female runner who collapsed near the finish line. Bystanders report she was running for more than 4 hours and had been drinking water at every aid station. On scene, the patient is confused and vomiting. Her skin is cool and clammy, no signs of trauma. Friends say she didn’t eat or take electrolyte supplements during the race.
Is this heat exhaustion from prolonged exertion or exertional hyponatremia from overhydration without sodium replacement?
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☀️ Diagnosis A: Heat exhaustion
Heat exhaustion occurs when the body overheats and cannot effectively cool itself, typically due to high temperatures, strenuous activity and inadequate fluid intake. It’s part of the heat illness spectrum and may progress to heat stroke if untreated.
Common symptoms of heat exhaustion:
- Profuse sweating
- Pale, cool or clammy skin
- Fatigue or weakness
- Dizziness or lightheadedness
- Nausea or vomiting
- Headache
- Muscle cramps
- Tachycardia and mild hypotension
- Normal or slightly elevated body temperature
How to manage heat exhaustion symptoms:
- Stop activity immediately and move to a cooler, shaded environment
- Remove excess clothing and equipment to allow heat dissipation
- Hydrate with cool fluids, preferably with electrolytes
- Apply cool, wet cloths or misting fans to assist with evaporative cooling
- Rest until symptoms fully resolve — do not resume activity prematurely
- Monitor for worsening signs, such as confusion or cessation of sweating
How patients with heat exhaustion present to EMS:
Patients with heat exhaustion often present after strenuous activity in hot or humid environments. They are typically alert but may complain of dizziness, weakness or nausea. Skin is usually cool, pale and sweaty. Vital signs often show tachycardia and low-normal blood pressure. Mental status is usually intact, but fatigue and irritability are common. Core temperature may be normal or mildly elevated, typically below 104°F (40°C).
EMS management of heat exhaustion:
- Move the patient to a shaded or air-conditioned environment
- Loosen or remove heavy clothing or gear
- Initiate active cooling (cool packs to neck, armpits, groin; fans; misting)
- Encourage oral fluids with electrolytes if patient is alert and not vomiting
- Administer IV fluids if dehydration is suspected and patient cannot tolerate oral intake
- Monitor vital signs and mental status for signs of progression to heat stroke
- Transport if symptoms do not improve rapidly or if worsening is observed
💦 Diagnosis B: Exertional hyponatremia
Exertional hyponatremia, on the other hand, results from excessive water intake that dilutes serum sodium levels, often during prolonged exertion. Sodium loss through sweat combined with overhydration disrupts electrolyte balance and cellular function.
Common symptoms of exertional hyponatremia
- Headache
- Nausea and vomiting
- Bloating or abdominal discomfort
- Confusion or altered mental status
- Muscle cramps or weakness
- Swelling of hands, feet or face
- Seizures (in severe cases)
- Decreased coordination or stumbling gait
How patients can manage exertional hyponatremia:
- Limit free water intake during prolonged activity — drink to thirst, not on a set schedule
- Use electrolyte-containing sports drinks instead of plain water
- Consume salty snacks or sodium supplements during endurance events
- Monitor weight changes during training — gaining weight may indicate overhydration
- Educate themselves on the risks of overhydration before participating in long-duration events
- Seek medical evaluation for persistent symptoms after exertion
How patients with exertional hyponatremia present to EMS:
Patients typically present during or shortly after extended exertion, such as running, rucking, or fireground operations. They may appear confused, nauseated, or lethargic. Friends or teammates may report the patient drank large volumes of water but had little food or electrolyte intake. Seizures or sudden mental status changes are critical red flags. Vitals may show normal or low temperature, bradycardia, or normotension. Swelling of extremities may be noted.
EMS management of exertional hyponatremia:
- Remove the patient from physical activity and monitor in a shaded or cool environment
- Conduct a thorough assessment, including neurologic status and fluid history
- Avoid administering hypotonic fluids (including plain IV saline) unless directed by medical control
- If severe symptoms (seizures, AMS), consider hypertonic saline per protocol or consult
- Initiate rapid transport for hospital management
- Reassess airway, breathing, and circulation continuously—monitor for signs of cerebral edema
- Document intake history, duration of exertion, and any witnessed seizures or collapse
🔍 Heat exhaustion vs. exertional hyponatremia: Spot the differences
Both conditions can present with similar nonspecific symptoms, such as nausea, vomiting, and malaise. However, altered mental status with seizures or profound confusion is more common in hyponatremia and may indicate cerebral edema. Profuse sweating and rapid heart rate typically point toward heat exhaustion.
In the field, EMS providers must avoid reflexively giving IV fluids until differentiating the cause. In hyponatremia, isotonic or hypotonic fluids may worsen cerebral edema.
Bottom line for EMS
When treating a collapsed responder or patient during or after exertion in the heat, assess fluid history, sodium losses and symptom profile carefully. Early field recognition of exertional hyponatremia vs. heat exhaustion can make the difference between rapid recovery and critical deterioration.
EMS1 is using generative AI to create some content that is edited and fact-checked by our editors.
