How your body responds to lack of oxygen

The altitude problem for your body is the shortage of oxygen. As you climb higher, the air gets thinner. At 4200 metres (the highest point on the Classic Inca Trail) atmospheric pressure is little over half its sea level value; at 5000 metres (the highest on Salkantay) it is lower still. Approaching these altitudes, each lungful gives you about half as much oxygen as at sea level, so your heart and lungs have to work twice as hard to maintain oxygen supply to your tissues.

Basically, your heart is the pump that makes your blood circulate. The lungs load the vital oxygen into your red blood cells for delivery to your tissues (muscles, brain and other organs). The demand from your muscles depends on their activity level, but your brain needs a surprising amount of oxygen (15% of the total). If your brain lacks oxygen, your judgement declines, movement control suffers and speech becomes confused.

Your body responds in various ways to needing more oxygen:

• You breathe faster and deeper
• Your heart beats faster, increasing the oxygen circulating to your tissues and forcing blood into parts of your lungs which aren’t normally used
• Your body gets rid of excess fluid and creates more red blood cells, making the blood thicker.

The timescale of these responses varies:you start to breathe faster right away, and your heart rate rises within minutes. It can take several days before your blood starts to thicken: if you notice that you are urinating a lot, that is probably a sign that your body is acciimatising. Making more red blood cells is a much longer process, taking a week or two to get under way: on most schedules, this won’t happen in time to make much difference.

At altitude, breathe deeply and freely as far as possible. Sleep is an important time for the body’s adjustment. Avoid sleeping pills and alcohol, both of which depress breathing while asieep. Allow digestión time after your evening meal before going to sleep.

Be aware of some other effects of altitude. Some people (especially women) experience swollen hands, face and ankles, so remove any tight-fitting jewellery before going to altitude. Contact lens wearers may find that the lenses become painful to wear at altitude, and should take spectacles as an alternative. Many people find they make more intestinal gas at altitude, but this is harmless unless your companions lack a sense of humour.

Acute Mountain Sickness (AMS)

Acute Mountain Sickness is what medical people call altitude sickness. “Acute” here means that the onset is sudden, not that you will be acutely ill. If mild or moderate, AMS symptoms may disappear if you rest and ascend no further; if they are severe, you must descend. If you ignore the symptoms and behave unwisely you might become seriously ill.

Individuals vary widely in how they respond to altitude. Factors such as age and gender affect your chances, although doctors cannot explain why. Females are less likely to experience AMS than males. At moderate altitude, young people are more likely to suffer AMS than their elders: the risk decreases with age in an almost straight line.

You need to recognise whether AMS is mild, moderate or severe. Mild AMS feels like a hangover and can affect people at any altitude above 2100 metres (7000 feet), occasionally even lower. Its commonest symptom is a headache (which should respond to aspirin, paracetamol or ibuprofen) combined with at least one of the following:

• Feeling sick
• Lack of appetite
• Sleeplessness eneral malaise (feeling lousy, lacking energy).

Altitude has a dehydrating effect, and dehydration alone can cause headaches. So if you have a headache, first drink a litre of water, perhaps with a mild pain-killer. If the headache disappears and you have no other symptoms, your body was just reminding you to drink more fluid. Mild AMS is bearable, and if it goes away after a rest or a downhill stretch you will be able to continue walking.

Moderate AMS is seriously unpleasant, whereas severe AMS is dangerous and could even be fatal if you were rash enough to ignore the symptoms. Moderate AMS differs from mild in that:

• There is likely to be vomiting
• the headache does not respond to pain relief, and
• the victim may be very short of breath even when not exercising (eg after 15 minutes’ rest).

Severe AMS can develop from moderate AMS if symptoms are ignored; it may involve ataxia (loss of muscular co-ordination and balance), altered mental states such as confusion, aggression or withdrawal, and serious complications followed, if untreated, by death.

Severe AMS or complications are very unlikely on the Inca Trail if you follow a sensible itinerary and react appropriately to any warning signs. Any symptoms that persist overnight should be taken seriously.

In summary, AMS is avoidable and treatable, very simply, as follows:

• If you have altitude symptoms, rest, drink fluids and do not ascend further until they disappear
• If you are getting worse, or have complications, descend at once.

Diamox, coca and other drugs for the Inca Trail Hike

The medical research literature on drugs and altitude illness is extensive, and acetazolamide (trade name Diamox) has been studied for over 25 years. When you exert yourself at altitude, you pant, venting off a lot of carbon dioxide; this can reduce the acidity of your blood. Diamox blocks or slows the enzyme involved in converting carbon dioxide, thereby stopping the blood from becoming too alkaline and stimulating the rate and depth of breathing. As a result, it speeds up acclimatisation. Some people take Diamox with them because it can help to prevent, as well as treat, AMS.

In most countries,you need a doctor’s prescription for Diamox. Before rushing off to get one, however, consider the possible downside. It has been known to cause severe allergic reactions in a few individuals. So you should try it out ahead of your trip to test if you are allergic, to experiment with dosage and to discover whether you can tolerate the side-effects. These include:

• Increased flow of urine (diuresis)
• Numbness or tingling in hands,feet and face
• Nausea and/or bizarre dreams
• Finding that carbonated drinks taste flat.

Since altitude has a diuretic effect anyway, many people prefer to avoid Diamox as it creates further interruptions to sleep in order to urinate. Some doctors say this is a problem of excess dosage. The recommended dosage used to be 250 mg three times a day, starting several days before ascending. Stephen Bezruchka suggests trying 125 mg daily at bedtime starting on the day before ascending, and increasing the dosage only if need be. Medical authorities tend to favour Diamox, especially for the minority who are unusually susceptible to altitude symptoms. However, most hikers don’t need it, and a few who use it have symptoms regardless.

Coca leaves have been chewed in the Andes for thousands of years and are an important part of the indigenous culture. In Inca times, coca was reserved for those of noble birth, but the Spanish gave it to overworked labourers to suppress hunger and fatigue. Its anaesthetic effect may help to mask altitude symptoms such as headaches, but it doesn’t affect the underlying physiology in the same way as Diamox. AMS is rare among residents because they are acclimatised, rather than because they chew coca leaves.

When people chew a quid of leaves together with a catalyst called llipta, a natural anaesthetic is released. This is not cocaine, a highly refined alkaloid, although coca leaves are the raw material from which this class A narcotic is made. You are unlikely to find coca-chewing addictive, and some people find it unpleasant. Try drinking maté de coca, tea made from coca leaves, which is also alleged to relieve altitude symptoms. It is widely available in Cusco, but don’t take any home since in most countries coca leaf is a prohibited drug and its importation carries a prison sentence.

Finally, although coca leaves are legal and commonplace in Peru, do not assume that it is safe to buy or use other drugs: police informants are active, and drug use or possession carries a prison sentence of up to 15 years.

Advice on food and drink

Tour operators are responsible for food, fuel and cooking equipment, and their cooks produce plenty of palatable food despite difficult conditions for preparation and serving. Don’t expect a choice of menu, and if you are vegetarían or vegan, discuss this beforehand. A diet rich in carbohydrates helps to prevent altitude symptoms.

Bring some snacks such as dried fruit, trail mix, cereal bars or chocolate. They will boost your energy and morale and can be shared with others. Bring also some sweets because many people suffer very dry throats at altitude.

Few people carry sufficient water, and even fewer keep it handy. You dehydrate quickly when walking at altitude: every time you breathe out, you lose moisture. Also altitude has a diuretic effect, and especially when exercising you are continually losing water vapour as invisible sweat. Expect to drink two to four litres per day on top of the liquid you take with meals.

Try to drink before you become thirsty. A water bottle or bladder with tube (eg a Platypus) is ideal as it lets you take sips whenever needed without having to stop or fiddle with rucksacks. (Disposable plastic water bottles are not allowed on the Inca Trail because of the litter problem, but refillable water bottles or bladders are fine.) If in doubt, check the colour of your urine: pale straw colour is healthy, but yellow warns that you are dehydrated.

Keep water purification drops or tablets handy and carefully follow the instructions about standing time and dosage in cold conditions. If the flavour bothers you, neutralise it with Vitamin C tablets or fruit-flavoured powder.

Help to limit fluid lost through sweating by adjusting your clothing. Try to anticipate your body’s heat production. Shed excess layer(s) just before you start to overheat, and restore them just before you start to chill (eg for a rest stop or when the weather changes). Because each of these actions means stopping and fiddling with your rucksack, it may be easier to keep a steady pace and wear clothes designed for flexibility. For example, jackets should have underarm zippers and pockets large enough to hold gloves and hat.

At altitude, keep your water bottle or bladder well insulated or warmed by your body heat, otherwise it could freeze during the night. If you use a water bladder, the narrow tube is prone to freeze, so either keep it protected or else blow back the water left in the tube after each sip so that it remains empty.

Summary: How to Prevent and Manage AMS at Inca Trail Trip

• Prepare well by becoming fitter (and giving up smoking if need be)
• Plan your trip to start with a few easy days at high altitude, eg Cusco
• Drink plenty of fluids (three to five litres per day), especially water
• Avoid sleeping pills and alcohol
• Eat small amounts of food often, even if you don’t feel hungry; avoid excessive salt
• If you have altitude symptoms, rest and do not ascend further until and unless you have recovered completely.