Heat exhaustion and heatstroke in Vietnam: telling them apart and cooling someone down

People read the temperature on a forecast and decide they can handle it, because they have handled that number somewhere dry. Then they spend an afternoon on a motorbike in Hue in July, or walk the full length of a beach road at midday. By late afternoon something has gone wrong. They cannot quite name it.

Heat illness sits on a slope rather than in two boxes. One line on that slope matters enormously. It is worth being able to spot. This page is about where that line is and what to do either side of it. It does not replace being examined by someone qualified.

When heat becomes an emergency

Heatstroke is a medical emergency. The brain is the organ at risk. Call 115 or get the person to the nearest hospital immediately, and start cooling them while you wait — do not choose one or the other:

• Confusion, slurred words, behaving out of character, or not knowing where they are
• A seizure, or collapse with loss of consciousness
• Skin that is hot and has stopped sweating altogether, although it can still be wet in a humid climate
• A temperature that stays very high after half an hour in the shade with cooling under way
• Repeated vomiting that makes drinking impossible
• Breathing fast and shallow, with a racing pulse that does not settle on resting
• Any of this in a small child, someone elderly, or someone with a heart or kidney condition — act sooner, not later

In heatstroke the body has lost the argument. It can no longer shed heat, and the temperature keeps climbing on its own. Cooling is the treatment, and it works better the earlier it starts.

Why humidity, not the number, is the problem

Sweat only cools you when it evaporates. In air already holding a great deal of water, it runs off instead, and the body loses the one mechanism it relies on. That is why a humid thirty-three degrees on the Vietnamese coast is harder work than a dry thirty-eight somewhere inland and arid. Visitors confident about heat keep getting caught.

Two practical consequences. Shade helps less than people expect, because shade removes radiant heat but not humidity. And a breeze helps more than it looks like it should. In a room that already feels wet, a fan is worth more than it costs.

Heat exhaustion: still fixable where you are

This is the stage where the body is struggling but still in charge. The person is unwell, often badly, but they know who and where they are. Treated properly in the shade, most people are substantially better within half an hour and fine the next day.

• Heavy sweating, pale and clammy skin
• Headache, dizziness, feeling faint on standing up
• Cramps in the calves, thighs or abdomen
• Nausea, and no interest in food
• Deep tiredness and weakness out of proportion to the walk
• A fast pulse and fast breathing that recover with rest
• Dark urine, and less of it than usual

Cooling someone down, in order

The sequence is simple and the order matters, because the first two steps do most of the work:

• Get them out of the heat — indoors with air conditioning if there is any, otherwise deep shade with moving air
• Take off excess clothing. A long-sleeved shirt and a helmet have been trapping heat all afternoon
• Wet the skin: a sponge, a wet towel, a shower set to cool rather than cold. Then keep air moving across it, with a fan or by fanning them
• Cold packs wrapped in cloth into the armpits, the groin and the sides of the neck, where large vessels run close to the surface
• Sips of cool water or oral rehydration salts if they are fully awake and can swallow safely
• Lie them down with the legs raised a little if they feel faint, and stay with them

What makes it worse

• Ice baths and ice-cold water poured onto someone who is conscious — the shock drives surface blood vessels shut and can trap heat inside
• Giving anything to drink to a person who is drowsy or confused, which risks it going into the lungs
• Alcohol, strong coffee and energy drinks, all of which pull in the wrong direction
• Paracetamol or ibuprofen for the high temperature — heat illness is not fever, and neither medicine lowers a heat load
• Salt tablets swallowed on their own without water
• Walking them somewhere, including to a vehicle, when they can be cooled where they are
• Deciding they are better and going back out the same day

Who gets caught, and when

The pattern across a season is consistent. Cyclists and motorbike riders in the middle of the day, because the airflow feels cooling while sun and road heat accumulate. Runners who kept their usual home schedule. People on day two or three of a trip, before any acclimatisation has happened — that process takes something like a week or two of regular exposure, and it is lost again within a few weeks of air-conditioned offices.

Then the groups where the margin is thinner. Older travellers, who feel thirst less reliably; small children, who heat up faster relative to their size; anyone on diuretics, beta blockers or some antidepressants and antihistamines; people with heart, lung or kidney conditions; and anyone who came out of a heavy night with a hangover, which is dehydration with a head start.

Drinking, salt, and the sweat you cannot see

In humid heat you lose fluid without noticing, because it never has the chance to evaporate visibly. Thirst lags behind the loss, and it lags further with age.

Water alone is right for ordinary days. For long hot days with real sweating, plain water on its own can leave sodium too low. It produces headache and nausea. Both read exactly like dehydration. Oral rehydration salts from any pharmacy solve that, and so does eating normally — salt arrives in food. Urine colour is a reasonable guide: pale is fine, dark means catch up.

After a bad afternoon

Someone who has had genuine heat exhaustion is more vulnerable for several days, not several hours. Plan the next day indoors or early. Keep drinking. Treat a return of headache and nausea as the same problem rather than a new one.

Anyone who had confusion, a seizure or a collapse needs assessment regardless of how well they look afterwards. Heatstroke can injure kidneys and muscle. Those injuries only show up in blood tests. That is not a judgement about how tough they are; it is simply what the tests are for.

What a clinician checks

• Core temperature, pulse, blood pressure lying and standing, and how alert the person is
• How much fluid has actually been lost, which is where self-assessment is least reliable
• Blood tests for sodium, kidney function and muscle breakdown when the episode was severe
• Intravenous fluid where drinking has stopped being enough, given as treatment rather than as a routine
• A review of regular medicines, because several of them reduce heat tolerance quietly
• A plain answer about hospital if the picture is heatstroke rather than exhaustion

The short version

Heat exhaustion is sweating, cramps, dizziness and weakness in someone who still knows where they are, and it is treated with shade, wet skin, moving air and fluid. Heatstroke is confusion, collapse or a seizure, and it is an emergency: call 115 or go to hospital straight away, and cool the person while help is coming.