The key to prevention of altitude sickness is a slow ascent. Patients flying to altitude should be counselled to rest on arrival until they feel well.
Patients going to very high altitude for the first time should ask, when booking, about the company's ascent profile, its previous record of summit success, the medical training of staff, the equipment and drugs carried and plans for accompanied evacuation for ill clients.
Acclimatisation to altitude starts rapidly with an increase in heart rate, followed by an increase in respiration rate that goes on for several days. This is accompanied by changes in the acid base balance in the blood mediated by the kidneys.
The mildest form of altitude illness is acute mountain sickness (AMS), which consists of some or all of the following symptoms: headache, nausea, vomiting, fatigue, anorexia, dizzi- ness and sleep disturbance. Because there are normally no clear physical signs, an open mind should be kept for any differential diagnosis. Symp- toms normally resolve over a few days if the patient does not ascend further.
The danger of AMS is that it can progress to the life-threatening high-altitude cerebral oedema (HACE) or highaltitude pulmonary oedema (HAPE), especially if the ascent is continued (see box below).
There is good evidence that acetazolamide works prophylactically for AMS. However, the dose of 750mg twice daily sometimes suggested is too high, and 250mg twice daily is an accepted regimen.
There is no evidence that other drugs work for prevention of AMS, with the exception of dexamethasone which can also be used to treat HACE.
Once AMS sets in, the treatment is rest without further ascent and mild analgesics for the headache until the symptoms settle.
For HAPE and/or HACE the only effective treatment is descent. Time can be bought by the immediate use of dexamethasone, 8mg by the most appropriate route, nifedipine modified-release tablets, 20mg three times daily, and acetazolamide. The use of a lightweight portable hyperbaric chamber, if available, may also help. But these treatments should never be used to facilitate staying high or further ascent.
Any decision about a pre-existing condition has to be based on a risk-versus-benefit assessment and the patient's attitude to risk.
There is data suggesting that asthma often improves at altitude, but patients should still use their normal medication. COPD that limits activity at sea level is a contraindication to high-altitude travel.
Controlled hypertension is not a contraindication but those with well-controlled angina should get specialist advice.
Sickle cell disease and any congenital heart problem with pulmonary hypertension are contraindications.
- Dr Hillebrandt is a GP in Holsworthy, Devon, and honorary medical adviser to the British Mountaineering Council
- The British Mountaineering Council's mountain medicine site www.thebmc.co.uk/world/mm/mm0.htm
COMPLICATIONS OF ALTITUDE SICKNESS
- Behaviour change.
- Decreased level of consciousness.
- Localising neurological signs.
- Dyspnoea (especially at rest and dry cough).
- Crackles on auscultation.
- Blood stained sputum.