Running 03 – Heatstroke and hyponatremia: two emergencies with opposite first aid

The water station at kilometer 35, close to ten in the morning. The sun is already above the treetops, and the road throws heat up to your knees. A volunteer in an orange shirt stands behind the row of tables, stacking cups with one hand and passing bottles to runners with the other. Within an hour, two people stop at this station and cannot go on. The first veers to the edge of the road, legs unsteady, asking again and again where they are, their skin burning hot. The second slumps down on the grass verge, vomits, and holds their head, complaining of a headache. Since the start of the race, this runner has stopped to drink at every station, two cups at some of them.

For both of them, the people standing nearby do almost exactly the same thing. They help them into the shade, fan them, lay a wet towel on the neck, open a bottle of water and put it right in their hands. For the first runner, that is far too little. For the second, the bottle of water is exactly what should not be given.

These two may be facing two completely different emergencies: exertional heatstroke and exercise-associated hyponatremia (low blood sodium). Both make a runner confused, both are common in long races in hot weather, and yet the way to handle them is almost the opposite. What follows matters most for the people standing nearby: running partners, supporters along the road, water station volunteers. Once a runner is confused, they can no longer look after themselves.

Burning hot and unable to speak in sentences

During long exertion in the sun, the body makes heat faster than it can get rid of it. Past a certain point, the heat disrupts how the brain works. Bystanders notice this in the runner’s mind before they notice it in the temperature. The runner gives wrong answers to simple questions, talks nonsense, weaves from side to side, then collapses. To the touch, the body is burning hot. That is exertional heatstroke. Measured in the rectum, body temperature is usually above 40 °C (American College of Sports Medicine, ACSM; Roberts and colleagues, 2021; Jameson and colleagues, 2018).

The figure of 40 °C is often misunderstood. A high temperature alone is not enough to call it heatstroke, because the diagnosis rests on a high body temperature together with a disturbance of the nervous system. Bystanders also don’t have to wait for a measurement. If you see a runner who is confused and feels hot under the sun, start cooling right away, and at the same time get someone to call 115 (emergency).

Someone who is only tired, hot and sweating heavily but still alert and speaking clearly is in a much milder state. We class that as mild heat illness. The line between the two levels lies in the mind. As soon as the person starts to become drowsy or muddled in speech, it has moved into the severe level.

A tub of ice water instead of a wet towel

The heat illness guidelines of the Wilderness Medical Society (WMS; Eifling and colleagues, 2024) put first immersing the person in ice water, or the coldest water available, covering the whole body up to the neck. This recommendation is graded strong, based on high-quality evidence. With immersion, body temperature falls by about 0.20 °C per minute; covering with wet towels manages only about 0.11 °C. That works out to ten minutes in the tub bringing the temperature down by about 2 °C, and ten minutes under towels by only about 1 °C.

Without a tub, pour water continuously over the whole body while fanning at the same time, or cover the whole body with ice packs. A few packs placed at the neck, armpits and groin do not count as covering. The WMS still strongly recommends both of these methods, although the evidence for them is weaker. At a water station, in our view, use whatever is at hand right away: the ice chest for chilling bottles, buckets of water, the large water containers on the tables.

Cool on the spot first, transport afterward. A medical team with a thermometer will cool the person to about 38.3–38.8 °C and then stop. Do not give fever-reducing medicine, because this person is hot from exertion, not from a fever. Someone with heatstroke needs intravenous fluids, and that is for medical staff to do, so don’t try to force water into the mouth of someone who is confused (Eifling and colleagues, 2024; Roberts and colleagues, 2021; Hosokawa and colleagues, 2021; Jameson and colleagues, 2018).

Many people believe that ice packs at the neck, armpits and groin are enough. That is true for mild heat illness, but not for heatstroke. Some people are also wary of ice water immersion for fear of harming the heart. The cardiovascular warning in the sports injury textbook by Joyce and Lewindon (2016) is about cold immersion to boost performance, not about emergencies. Taking an ice bath on your own after an ordinary run to recover faster is best avoided, but a person with heatstroke needs to be immersed right away.

For mild heat illness, Vietnam’s Ministry of Health advises cool towels or ice at the neck, armpits and groin, along with Oresol (oral rehydration salts). Mix Oresol at exactly the dose on the packet, and drink according to thirst, without forcing it. If the person starts to become drowsy, call 115 and switch to whole-body cooling as described above.

A bottle of water held out at the wrong moment

Exercise-associated hyponatremia (EAH) is when the sodium in the blood falls below 135 mmol/L, during exercise or within 24 hours afterward (Hew-Butler and colleagues, 2015). The signs are nausea, vomiting, headache, then confusion; in severe cases, seizures. The typical scene is after a long distance, in someone who has drunk a lot, drinking steadily at every station, and even taking salt tablets cannot prevent it if the amount of water is still too much (Bennett and colleagues, 2020). The 24-hour mark reminds families that symptoms can come on even after the runner has got home.

The first thing is not to give any more water. This advice sounds backward, because in Vietnam we are used to handing a glass of water to anyone who looks tired. Take the person to the medical point and call 115. There, treatment is based on the level of symptoms, not just the sodium number. People with severe symptoms are given hypertonic saline (salt water more concentrated than blood), and that is the job of medical staff; there is no dose for bystanders to give on their own (Hew-Butler and colleagues, 2015; WMS, Bennett and colleagues, 2020).

EAH is not always caused by drinking too much. Hoffman and colleagues (2013) followed a 161 km race in hot weather and found hyponatremia in 15.1% of runners, ranging from 4.6% to 51% depending on the year. More than a third of those people (35.6%) were in fact dehydrated. In ultra trail running (running on mountain paths, over distances longer than a marathon), one review recorded an EAH rate of about 9.1% (Lecina and colleagues, 2022). Someone with dry lips who looks short of water may still have low sodium, and you cannot tell the difference by looking.

When you don’t know which one it is

Out on the course, bystanders are rarely sure which one they are facing.

Signs	Think of	Do right away	Don’t
Confusion, talking nonsense, collapse, body burning hot under the sun	Heatstroke	Cool the whole body right away: immerse up to the neck in ice water or cold water; without a tub, pour water and fan, or cover the whole body with ice packs; call 115	Wait to measure the temperature; cool only the neck, armpits and groin; give fever-reducing medicine; try to make them drink water
Tired, hot, sweating heavily but still alert and speaking clearly	Mild heat illness	Move into the shade; cool towels or ice at the neck, armpits and groin; Oresol mixed at the correct dose, drunk according to thirst	Force them to drink several bottles in a row; leave them alone once they start to become drowsy
Nausea, vomiting, headache, confusion, seizures after a long run, having drunk a lot	Hyponatremia	Stop giving drinks; take them to medical staff, call 115	Give more water to “bring them round”; give salt on your own based on word of mouth
Confusion after running, unclear which type	One of the two, or another cause	Take them to medical staff to measure sodium and body temperature	Guess by looking and then give lots of water

Whether you think it is heatstroke or hyponatremia, do not give a confused runner anything to drink. Someone with heatstroke needs intravenous fluids, someone with hyponatremia needs water stopped, so the water station’s bottle helps neither of them. In our view, if the person is burning hot while you wait, you should still cool them. In trail races that run through the night in the mountains, in wind and rain, confusion can also be caused by hypothermia, and then the person needs to be kept warm (Jameson and colleagues, 2018).

The eighth-month sun that browns the pomelo

Our grandparents said, “the sun of the eighth month browns the pomelo.” Into autumn, the sun is still harsh enough, and our year-end race season has many stretches run under that sun. Prevention comes down to a few things:

• Runners need to get used to the heat before the race. The WMS (Eifling and colleagues, 2024) sets a mark of at least 7 days, with 1–2 hours of activity in hot weather each day; Joyce and Lewindon (2016) note that most adaptation takes 10–14 days. If someone in the group has just come from a cool place to a hot race, running partners and station volunteers should keep a closer eye on them;
• Avoid training in the sun between 10:00 and 16:00;
• Drink when you are thirsty; don’t force yourself to drink on a schedule;
• In long races in hot, humid weather, use drinks that contain sodium;
• If you run in a group, agree on this in advance. If you see a friend speaking strangely or walking unsteadily, pull them off the course; don’t let them carry on to finish the distance.

Getting used to the heat has another benefit. After adaptation, people sweat more, yet the amount of sodium lost in sweat falls by about 22–59% (Brown and colleagues, 2022). The WMS also advises relying on the WBGT (wet-bulb globe temperature) index, which combines temperature, humidity, sun and wind, to decide whether to run, instead of looking only at the thermometer.

Summerheat stroke and the clinic’s part

The textbook of Chinese medicine theory says that the summerheat pathogen (暑邪, shǔ xié), that is, the heat of summer harming the body, tends to consume qi (耗气 / 耗氣, hào qì; draining strength) and injure body fluids, meaning fluids in the body such as sweat and saliva (Basic Theory of Chinese Medicine, 中医基础理论 / 中醫基礎理論, p. 386, 498). The traditional healer (lương y) Nguyen Huu Duc teaches the use of Qing Shu Yi Qi Tang (清暑益气汤 / 清暑益氣湯, Clear Summerheat and Augment the Qi Decoction) for summerheat stroke (中暑, zhòng shǔ; being harmed by summer heat, a kind of sunstroke), treating it as “an urgent situation” and not something to take for everyday prevention (Classical Formulas, 2017). For someone who has collapsed and is confused in the middle of the course, no herbal formula can do the job of a tub of ice water and an ambulance.

In summer there is also an herb often mentioned in many formulas for releasing colds: Xiang ru (Mosla chinensis aerial parts). The formula Xiang Ru San (香薷散, Mosla Powder) was originally meant for people who catch a cold in summer and do not sweat (Formulas, 方剂学 / 方劑學, p. 143). The herb Xiang ru itself should be avoided when there is already heavy sweating and when someone has been harmed by summer heat (Chinese Materia Medica, 中药学 / 中藥學, edited by Zhong Gansheng, p. 155–156), so it does not suit a runner who is drenched in sweat.

Someone who is confused right after a race needs 115, not a clinic. The clinic does its own part before and after the race season. The doctor reviews the medicines you are taking; anti-inflammatory painkillers are considered a factor that may increase the risk of hyponatremia, although the data are still conflicting (Hew-Butler and colleagues, 2015).

People who, after each hot running season, tend to sweat heavily and feel thirsty, short of breath and worn out are described in traditional medicine as having dual deficiency of qi and yin (气阴两虚 / 氣陰兩虛, qì yīn liǎng xū), meaning both qi (strength) and yin (the fluids that nourish the body) are depleted. After the examination, the doctor may prescribe a decoction in ready-to-drink 50 ml pouches matched to that pattern. The pouches cannot replace water and salt, and there is no evidence that they prevent heatstroke. Formulas in this direction usually contain herbs that reduce sweating, while during a run the body needs sweat to get rid of heat (Formulas, p. 180–181). That is why the clinic advises not taking these pouches within 2 hours before a run in the heat or before a race; water is still drunk according to thirst.

A few weeks after the water station

Applied Kinesiology (AK, a way of testing the strength of each muscle by hand) has no place in the acute episode. For someone who has had heat illness, heatstroke or hyponatremia, the AK part only begins once they have fully recovered. Those who had to go to hospital have been discharged. Blood sodium, muscle enzymes and kidney function are back to normal, and they are eating, sleeping and moving about normally.

Picture the first runner at the water station. A few weeks later, the test results are back to normal, and after a few short runs, the inner side of their knee starts to ache. The AK doctor immediately thinks of the sun on that day. Walther lists extreme heat and training sessions dragged out to exhaustion among the things that load onto the adrenal glands (small glands sitting on top of the kidneys that help the body cope with stress), glands he links to the sartorius and gracilis, two long muscles that support the inner knee (Synopsis, p. 200, 322–323).

So the doctor tests those two muscles first, then looks at the pelvis. When the adrenal glands work poorly for a long time, the sartorius and gracilis tend to work below threshold (when tested by hand, they cannot hold their force), bringing inner knee pain and a pelvis shifted backward. Walther notes that this kind of pain comes back easily until the adrenal glands are stable again (p. 464–465). For any muscle that tests weak, the doctor stimulates its NeuroLymphatic and NeuroVascular reflex points. For the shifted pelvis, the doctor first tests which direction makes the muscle strong again, then mobilizes it in exactly that direction with a gentle movement at the joint. After that, the sartorius and gracilis are retested.

The day you start running again is still decided by the doctor who treated the acute episode. The AK part looks after the muscles around the knee and pelvis.

When to see a doctor

After a race, there are a few signs you should not wait out. Urine as dark as cola, severe muscle swelling and pain, and passing little urine may be rhabdomyolysis (muscle breaking down on a large scale), which needs tests of muscle enzymes and kidney function (Jameson and colleagues, 2018). If you have had heat illness in the middle of a race, often feel worn out, get an aching inner knee whenever you return to running after the hot season, or want to review your medicines and supplements before your next race, bring everything you are taking to the appointment. Book a consultation.

Back to the water station at kilometer 35

The first runner at the water station needed the ice chest and buckets of water poured over them continuously; one more wet towel would not have been enough. The second needed someone to call the medical team. The volunteer in the orange shirt did not have to get the diagnosis right, only to avoid doing the opposite of what each person needed.

At a water station, sometimes the most helpful thing you can do is put the bottle of water away.

Worth keeping

• If a runner is confused, talking nonsense and burning hot, cool the whole body right away, without waiting to measure the temperature;
• With a tub, immerse up to the neck in ice water or the coldest water available; without a tub, pour water continuously while fanning, or cover the whole body with ice packs;
• Cool on the spot first, call 115 at the same time, transfer to hospital afterward;
• Someone with nausea, headache or confusion after a long run who has already drunk a lot: give no more water, take them to medical staff;
• Do not give a confused person anything to drink, whether you think it is heatstroke or hyponatremia;
• Mild heat illness, still alert: cool the neck, armpits and groin, and drink Oresol mixed at the correct dose, according to thirst;
• Before a hot race, train in the heat for 1–2 hours a day, for at least 7 days.

References

Sources in Vietnamese

• Bộ Y tế (Cục Quản lý Môi trường y tế). 2023. Hướng dẫn chăm sóc sức khỏe mùa nắng nóng cho cộng đồng và người lao động (ban hành kèm văn bản số 356/MT ngày 19/5/2023). Cổng thông tin Bộ Y tế, đăng ngày 22/5/2023. https://moh.gov.vn/tin-lien-quan/-/asset_publisher/vjYyM7O9aWnX/content/bo-y-te-huong-dan-cham-soc-suc-khoe-mua-nang-nong-cho-cong-ong-va-nguoi-lao-ong (trang gốc nay không mở được; bản lưu ngày 7/12/2025: http://web.archive.org/web/20251207001617/https://moh.gov.vn/tin-lien-quan/-/asset_publisher/vjYyM7O9aWnX/content/bo-y-te-huong-dan-cham-soc-suc-khoe-mua-nang-nong-cho-cong-ong-va-nguoi-lao-ong).
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