Altitude Sickness


As we ascend to high altitude our bodies have to acclimatize to the decreasing amount of oxygen in the atmosphere. Failure to acclimatize, usually due to a too rapid ascent above 2000m (6500ft), results in symptoms of altitude illness. These problems become common above 2500m (8200 ft) and present in the following ways:

  • Acute Mountain Sickness (AMS) is the most common and is not life-threatening
  • HACE (High Altitude Cerebral Edema) is a life-threatening illness that can develop from AMS
  • HAPE (High Altitude Pulmonary Edema) is a life-threatening illness; it may occur on its own, or with AMS or HACE

These three presentations of altitude illness can vary from mild to severe.

Preventing AMS, HACE and HAPE by acclimatising wisely

The most common preventable causes of altitude illness are gaining height too rapidly and over-exertion.

  • A conservative recommended rate of ascent is 300m (1000ft) per day with a rest day every third day up to 3500m (11500ft). Above that, 150m (500ft) per day with a rest day every three days. While many people can and do travel higher faster than this, the incidence of AMS rises proportionately
  • Walk at a steady plod with regular rest/drink breaks. There is no virtue in pushing on or striving to finish at the front. Aim to avoid getting out of breath.
  • If you are struggling to keep up with your group, do not hesitate to speak up so that timely help can be given.
  • Rest days must really be REST days for even the mildest symptoms of AMS.
  • While dehydration does not increase the risk of altitude illness, it does interfere with performance (so does over-hydration, especially without salts replacement). The only way to be sure you are drinking enough is to keep your urine ‘pale and plentiful’. This may mean drinking as much as 4 to 6 litres of fluids per day (as water, tea, soup, etc.)
  • Avoid all sedative drugs (antihistamines, tranquilizers, sleeping pills, etc.) as they suppress respiration and therefore increase the risk of altitude illness. This includes alcohol (drinking alcohol can give rise to social problems on a trek, especially if it is readily available. Better to save it for a celebration on return to lower altitude)

Acute Mountain Sickness (AMS)

AMS is common; depending on the altitude gained and the speed of ascent, incidence ranges from 20 to 80%. Typically symptoms appear anytime during the first 36 hours after an ascent. If you rest at the same altitude, symptoms usually disappear quickly (but can take up to 4 days) and you are now acclimatized to this altitude. AMS may reappear as you ascend higher still and acclimatization has to occur again.
Symptoms are due to fluid accumulation in brain tissue and vary from mild to severe; it can progress to HACE if it is ignored. People often blame cold, heat, infection, alcohol, insomnia, migraine or exercise for their AMS symptoms and carry on ascending. This has lead to many deaths from HACE or HAPE.
NB. It may be quite difficult to tell if a young child is developing AMS. The only symptoms may be increased fussiness, crying, loss of interest or loss of appetite.

Symptoms & signs

  • Headache (typically throbbing, often worse for bending over or lying down), PLUS one or more of the following symptoms:
  • Tiredness, weakness
  • Dizziness, light headedness
  • Loss of appetite, nausea (or vomiting)
  • Insomnia, disturbed sleep, frequent waking


  • Rest (avoid even the slightest exertion if this is possible) at the same (or lower) altitude until the symptoms clear (up to 4 days)
  • Drink enough to keep your urine pale and plentiful
  • Use ibuprofen or paracetamol for headache
  • Consider Diamox™ (125 to 250 mg 12-hourly) for 3 days, or for the rest of the time at altitude if symptoms return
  • Consider Stemeti™l (or other anti-vomiting medication) for persistent nausea/vomiting
  • If AMS symptoms are severe, give oxygen (1 to 2 L/min) OR use a pressure bag until symptoms clear
  • Check the victim regularly for signs of HAPE and HACE, especially during the night
  •  Descend far enough to clear symptoms (at least 500m/1640ft) if symptoms of AMS do not improve or get worse

Facts on HAPE & HACE

  • HACE or HAPE occur in approximately 1 to 2% of people going to high altitude
  • HAPE and HACE may occur alone or together
  • HAPE is roughly twice as common as HACE
  • HAPE causes many more deaths than HACE
  • HAPE may appear without any preceding symptoms of AMS
  • HAPE is more likely in people with colds or chest infections
  • HAPE often comes on after the second night spent at a higher altitude
  • HAPE can develop even after descending from a higher altitude
  • HACE usually develops after symptoms of AMS have appeared and often gets rapidly worse during the night
  • HACE may develop in the later stages of HAPE

HACE (High Altitude Cerebral Edema)

Symptoms of HACE are caused by an accumulation of fluid in or around the brain. Typically symptoms and signs of AMS become worse and HACE develops. Someone with HAPE may also develop HACE.

Symptoms & signs

  • Severe headache, which often feels worse on lying down and is not relieved by ibuprofen, paracetamol or aspirin
  • Tiredness, severe fatigue
  • Nausea and/or vomiting which may be severe and persistent
  • Loss of coordination, clumsiness. The victim needs help with simple tasks such as tying their shoelaces or packing their bag. They cannot do the finger-nose test
  • Staggering, falling. They cannot do the heel-to-toe walking test or the standing test
  • Blurred or double vision, seeing haloes around objects
  • Loss of mental abilities such as memory. They cannot do a simple mental arithmetic test
  • Confusion, hallucinations
  • Change in behaviour (aggression, apathy, etc.)
  • Drowsiness, difficult to wake up, coma, death

Tests for HACE

  • Heel-to-toe walking test: The victim is asked to take 10 very small steps, placing the heel of one foot to the toes of the other foot as they go. Reasonably flat ground is necessary and the victim should not be helped
  • Standing test: The victim stands with eyes closed, feet together and arms by their sides
  • Finger-nose test: With eyes closed, the victim repeatedly and rapidly alternates between touching the tip of their nose with an index finger then extending this arm to point into the distance (a useful test if the victim is in a sleeping bag)
  • Mental arithmetic test: Give the victim a mental arithmetic test, eg. subtract 7 from 100, 7 from 93, and so on (but remember some people may be poor at arithmetic even at sea level)

If the victim cannot do any of the above tests easily (or refuses to cooperate), or show excess wobbling or falling over in the two first tests (be prepared to catch the victim if they fall over!), assume they are suffering from HACE. If in doubt about the victim’s performance, compare with a healthy individual. Be prepared to keep repeating these tests.


  • Descend immediately (prompt descent will begin to reverse the symptoms). Descend as low as possible, at least 1000m/3280 ft. Descend at night or in bad weather if necessary. Carry the victim if possible, as the exertion of walking can make the illness worse
  • If descent is not immediately possible (eg. dangerous terrain or weather, not enough helpers or while waiting for a helicopter), oxygen or the use of a PAC and appropriate medications will keep the person alive until descent can be undertaken
  • Give oxygen:

- From a bottle using a mask (2 to 4 L/min), OR
- By using a pressure bag (this is roughly the equivalent of 2 to 4 L of oxygen/min)
NB: If both oxygen and a pressure bag are available, give the oxygen while the bag is being prepared and after the victim comes out of the bag. Do not give oxygen inside the bag unless it is designed for this purpose and you have been trained to do so.

  • Give medications: -8 mg of dexamethasone at once (by mouth, IV or IM) followed by 4 mg 6-hourly. Dexamethasone takes several hours to work. Stop it once below 2500m/8200ft AND after at least 3 days of treatment by tailing off the dose slowly (give the last 3 doses 12-hourly)- Diamox™ 250 mg 8 to12-hourly- Treat persistent vomiting with anti-vomiting medication
  • Prop the victim up in a semi-reclining position as lying down flat may make their condition worse
  • Avoid even the slightest exertion if this is possible. Even walking a few steps may make their symptoms worse or reappear. Do not leave the victim alone
  • If a person is turning blue or is falling into unconsciousness, give them rescue breathing before they stop breathing

HAPE (High Altitude Pulmonary Edema)

Symptoms of HAPE are due to the accumulation of fluid in or around the lungs. It may appear on its own without any preceding symptoms of AMS (this happens in about 50% of cases), or it may develop at the same time as AMS. HAPE can easily be mistaken for a chest infection or asthma: if in doubt treat for both.

Symptoms & signs

  • A reduction in physical performance (tiredness, severe fatigue) and a dry cough are often the earliest signs that HAPE is developing
  • Breathlessness. In the early stages of HAPE, this may mean just taking a bit longer to get one’s breath back on resting after mild exercise. Later on, there is marked breathlessness with mild exercise. Finally, breathlessness occurs at rest. Record the respiratory rate (NB: At 6000m/19700ft, normal acclimatized respiration rate is up to 20 breaths per minute)
  • The dry cough may later become wet with frothy sputum, which may be blood stained (pink or rust coloured). This is a serious sign
  • “Wet” sounds in the lungs when breathing in deeply (place your ear on the bare skin of the victim’s back below the shoulder blades; compare with a healthy person). Note: There may be NO wet sounds in even quite severe HAPE: this is called ‘dry HAPE’
  • There may be: mild fever up to 38.5ºC, a sense of inner cold, pains in the chest
  • Blueness or darkness of face, lips, tongue or nails due to lack of oxygen in the blood (cyanosis)
  • Drowsiness, difficulty waking up, coma, death


Same general treatment as for HACE, EXCEPT:

  • Give oxygen as for HACE but give the bottled oxygen at a rate of 4 to 6 L/min till recovering, then 2 to 4 L/min
  • Give medications:

- Nifedipine. This should only be used if bottled oxygen or a pressure chamber is not available and the victim is warm and well hydrated. Give the modified release (MR) form of the tablets (20 mg 12-hourly for 2 or 3 days). If a fall in blood pressure occurs due to nifedipine (pallor, weak rapid pulse, dizzy on standing), treat as shock
- Diamox™ 250 mg 8 to 12-hourly
- An asthma reliever spray (2 puffs 4-hourly) may help

Going back up again?

  • Anyone seriously ill with HACE or HAPE and needing oxygen, treatment in a pressure bag or dexamethasone/nifedipine, should descend immediately after treatment. As, even if they feel completely recovered, symptoms may rapidly rebound with exertion or further ascent.
  • Having descended and having become symptom-free at a lower altitude, they should not go up again as it is highly likely that the HACE or HAPE will reoccur (rebound)
  • If re-ascent is unavoidable (eg. driving out of Tibet over high passes), give Diamox™ 250 mg 12-hourly. If the original problem was HACE, add dexamethasone (4 mg 12-hourly); if the problem was HAPE, add modified release Nifedipine (20 mg 12-hourly). Give oxygen while crossing passes