Altitude sickness is a potentially - if rarely - fatal condition encountered at anything over 2000m, but likeliest and most serious at altitudes of 4000m and above. It can cause severe difficulties - but a little preparation should help you avoid the worst of its effects. In many South American countries it is known by the Quechua word soroche , but in Argentina is most commonly, and confusingly, called puna (the local word for altiplano or high Andean steppes). You'll also hear the verb apunar and the word apunamiento , referring to the state of suffering from puna , whether affecting humans or vehicles (which also need to be adjusted for these heights)

First, if you're driving into the altiplano make sure that your vehicle's engine has been properly adjusted. All engines labour because of the low oxygen levels, and when you start walking you'll empathize, so don't try to force the pace and stay in low gears. To avoid the effects of the puna on yourself, don't rush anywhere, but instead walk slowly and breathe steadily - and make things easier on yourself by not smoking. Whenever possible, acclimatize : it's better to spend a day or two at around 2000m and then 3000-3500m before climbing to 4000m or more, allowing the body to produce more red blood corpuscles rather than forcing it to cope with a sudden reduction in oxygen levels. And make sure you're fully rested; an all-night party isn't exactly the best preparation for a trip up into the Andes. As for drinking, alcohol is also best avoided, prior to or during high-altitude travel, and the best thing to drink is plenty of still water - never fizzy because it froths over or can even explode at high altitudes - or tea. Eating, too, needs some consideration: digestion uses up considerable quantities of oxygen, so snacking is preferable to copious lunches and dinners. Carry supplies of high-energy cereal bars, chocolate, dried fruit (the local raisins, prunes and dried apricots are delicious), walnuts or cashews, crackers and biscuits, avoiding anything that ferments in the stomach such as milk, fresh fruit and juices, vegetables or acidic food, as they're guaranteed to make you throw up if you're affected; the best - because it's the least acidic - form of sugar to ingest is honey. Grilled meat is fine, so asados are all right, but don't over-indulge.

Minor symptoms of the puna , such as headaches or a strange feeling of pressure inside the skull, nausea, loss of appetite, insomnia or dizziness, are nothing to worry about, but more severe problems, such as persistent migraines, repeated vomiting, severe breathing difficulties, excessive fatigue and a marked reduction in the need to urinate are of more concern. If you suffer from any of these, seek out medical advice at once and consider returning to a lower altitude. Severe respiratory problems should be treated immediately with oxygen, carried by tour operators on excursions to 3000m or more, as a legal requirement, but you're unlikely ever to need it.