Altitude sickness
Mountain air has the same composition as air at sea level, but it is thinner: every breath carries less oxygen.
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Medicines commonly prescribed for Altitude sickness
For informational purposes only. Always consult a doctor before using any medicine.
Dosage form: EYEDROP, 2 mg/1 packageActive substance: artificial tears and other indifferent preparationsManufacturer: Teva Pharma S.L.U.Prescription not requiredDosage form: ORAL SOLUTION/SUSPENSION DROPS, 13.3 mg prednisolone estragelate/mlActive substance: prednisoloneManufacturer: Laboratorios Sonphar S.L.Prescription requiredDosage form: EYEDROP, 5 mg/mlActive substance: artificial tears and other indifferent preparationsManufacturer: Neuraxpharm Spain S.L.Prescription not required
Mountain air has the same composition as air at sea level, but it is thinner: every breath carries less oxygen. The body does not register the shortfall straight away. It usually shows up a few hours after someone steps off a plane in a high-altitude city, rides a cable car up, or reaches a mountain pass. A headache, nausea and broken sleep on the first night up there are the commonest reaction, and in themselves they are not dangerous. Altitude sickness turns dangerous in two situations: when it is mistaken for tiredness, and when people keep climbing after it appears.
Why the body struggles up high
The share of oxygen in the air is the same on the beach as at four thousand metres — about 21 %. What changes is the pressure. The higher you go, the less firmly the air is pressed against the ground and the fewer oxygen molecules fit into each breath. At three thousand metres there is roughly a third less than you are used to; at five and a half thousand, half.
The body reacts at once: breathing speeds up, the pulse rises, within a couple of days the kidneys shift the acidity of the blood, and the bone marrow then starts turning out more red cells. That is acclimatisation. It is measured in days, not hours, and altitude sickness appears exactly where someone has climbed faster than the body could adjust.
For most people the threshold begins at around 2500 metres, and for some noticeably lower. What matters is not the point you reached during the day but the height at which you went to sleep: breathing slows during sleep, and blood oxygen falls furthest at night.
What ordinary mountain sickness looks like
Complaints start 6 to 12 hours after gaining height, rarely later than the first day. They almost always begin with the head.
- a pressing headache spread across the whole skull, worse towards morning, on bending and on coughing, and stubborn against the painkiller you normally rely on;
- nausea, loss of interest in food, sometimes vomiting;
- a weakness that makes a familiar stretch of trail twice as hard;
- dizziness and unsteadiness on the feet;
- fragmented sleep: you wake short of breath, and overnight the breathing speeds up and then pauses for a few seconds at a time;
- puffiness of the face, hands and ankles by morning.
The picture passes easily for dehydration, food poisoning or a hangover, and that is the main trap. Up high it is sensible to treat any feeling of illness as altitude sickness until something else is proven. Being wrong in that direction costs a lost day; being wrong the other way can cost a life. If you stop and climb no higher, the ordinary form settles within one to three days.
Brain swelling and fluid in the lungs: when hours count
Two rare forms of altitude sickness end differently: without descent a person dies within hours, at most within a day, and no medicine changes that.
High-altitude cerebral oedema usually grows out of mountain sickness that was ignored. Balance goes first: the person cannot walk a straight line heel to toe and lurches as though drunk. Then come confusion, odd behaviour, indifference to what is happening, deepening drowsiness and coma.
High-altitude pulmonary oedema can develop with no headache at all, often on the second night. The first sign is breathlessness at rest and a sudden collapse of stamina: the person drops behind on a stretch they walked easily the day before. A dry cough then turns wet, with frothy pink sputum, breathing bubbles audibly, lips and nails go blue, and lying down is harder than sitting up.
Descend immediately if you or a companion have even one of the following:
- disturbed balance or an unsteady walk;
- confusion, answers that make no sense, unexplained sleepiness;
- breathlessness at rest, or a cough bringing up frothy, pink or bloodstained sputum;
- blue lips, tongue or nails;
- vomiting that makes drinking impossible;
- a severe headache that does not lift with a painkiller and rest.
Descent is the one treatment that always works. Go down at night, in bad weather, halfway through a route — as soon as any of these signs is spotted. Nobody who is ill should be left on their own, and nobody should be sent down unaccompanied: within half an hour they may stop understanding where they are.
Who copes worst with height
Predicting the reaction in advance is close to impossible, but some things are known for certain.
- the speed of ascent counts for more than anything else: flying straight into a high city, or sleeping above three thousand metres on day one, is the commonest setup;
- previous episodes of altitude sickness are the best predictor of the next one;
- fitness offers no protection: trained people move faster and fall ill more often, and willpower does nothing here;
- children tolerate height no worse than adults, but in small children it all looks like crankiness, refusing food and listlessness, so it is harder to recognise;
- heart and lung conditions, severe anaemia, pulmonary hypertension, sleep apnoea and recent surgery all call for a conversation with a doctor before the trip;
- in sickle cell disease altitude can trigger a crisis, and in pregnancy nights spent high in the mountains are weighed up separately.
How to climb and avoid it
Prevention is a matter of scheduling, not of equipment.
- above 3000 metres, raise your sleeping height by no more than 300 to 500 metres a day;
- every three or four days, or every thousand metres gained, keep a day with no gain in height;
- work high, sleep low: you can go higher during the day provided you come back down for the night;
- if you flew straight up, spend the first day or two without exertion and without excursions higher still;
- drink to thirst and eat properly: forcing litres of water down is harmful, and carbohydrates are easier to digest at altitude;
- skip alcohol and sleeping tablets for the first nights, as both suppress breathing exactly when it is needed most;
- build spare days into the route and check whether your insurance covers evacuation from altitude.
For anyone who has been ill before or has to gain height quickly, a doctor may prescribe a drug from the carbonic anhydrase inhibitor group in advance; it speeds up the adjustment of breathing. That is a conversation to have before the trip, not something to borrow from a fellow traveller's kit.
What to do once it has started
The first and most important step is to stop: go no further and sleep no higher than the previous night until things settle.
Ordinary painkillers help the headache and anti-sickness medicines help the nausea. Alcohol and sleeping tablets are out. If there is no improvement within a day, descend 500 to 1000 metres — in most cases that is enough.
Bottled oxygen and a portable pressure bag are serious pieces of rescue kit, but they buy time rather than cure. The same goes for drugs: a carbonic anhydrase inhibitor speeds acclimatisation, a corticosteroid holds back brain swelling, and for fluid in the lungs medicines are used that lower the pressure in the lung vessels. Those last ones are not the blood pressure tablets somebody takes at home, and taking them out of another person's kit is dangerous. All of it makes sense only as support on the way down.
Climbing can resume once symptoms have gone completely and a full day has passed feeling well. After pulmonary or cerebral oedema, gaining more height on that trip is not up for discussion.
Online consultation
A remote appointment is most useful while you are still planning: the doctor goes through the itinerary by dates and sleeping altitudes, judges how it fits with your long-term conditions and regular medicines, discusses whether a preventive drug makes sense, and helps assemble a sensible kit instead of a random collection. After the trip it helps to work out whether altitude was behind the illness. Once symptoms have unfolded on the mountain, however, talking to a doctor replaces nothing: the decision to descend is made on the spot and without delay.
This material is for information only and does not replace medical advice.
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