Altitude Sickness on Nepal Treks: A Plain-Language Guide

Altitude is the single most serious health risk on a Himalayan trek, and also one of the most preventable. Every season people are evacuated, and a few die, because warning signs were ignored or a schedule was put ahead of a body. This guide covers the basics. It is general information, not medical advice; speak to a doctor before your trip, especially if you have a heart, lung or blood condition.

What happens at altitude

As you climb, air pressure falls and each breath delivers less oxygen. At 3,500 metres you take in roughly two-thirds of the oxygen available at sea level; at 5,500 metres, about half. The body adapts by breathing faster, raising the heart rate and, over days, making more red blood cells. This process is called acclimatisation, and it cannot be hurried.

Problems arise when you ascend faster than your body can adjust.

Who is at risk

Anyone. Fitness, youth and previous experience offer no protection. Marathon runners fall ill while unfit smokers stroll past. The strongest predictor is how you have reacted before, and even that is unreliable. Speed of ascent matters far more than who you are.

Acute mountain sickness (AMS)

The common, mild form usually appears six to twelve hours after arriving at a new height, typically above 2,500 metres.

Symptoms: headache, plus one or more of nausea or loss of appetite, tiredness, dizziness and disturbed sleep.

What to do: stop ascending. Rest at the same altitude, drink fluids, eat lightly and take a simple painkiller for the headache. Symptoms usually ease within a day or two, after which you can continue. If they get worse instead of better, go down.

The two dangerous forms

High-altitude cerebral oedema (HACE) is swelling of the brain. Signs include severe headache not relieved by painkillers, confusion, odd behaviour, drowsiness and loss of coordination. A simple test is to walk heel-to-toe along a straight line; someone with HACE staggers as if drunk.

High-altitude pulmonary oedema (HAPE) is fluid in the lungs. Signs include breathlessness at rest, a persistent cough that may produce frothy or pink sputum, extreme fatigue, a racing pulse and blueness of the lips.

Both can kill within hours. Both can occur without mild symptoms first. The treatment for either is the same and is not negotiable: descend immediately, even at night, by at least 500 to 1,000 metres, and seek medical help. Oxygen and certain medicines help but do not replace going down.

Prevention

1. Climb slowly. Above 3,000 metres, aim to raise your sleeping altitude by no more than 300 to 500 metres per day.

2. Take rest days. Spend an extra night for every 1,000 metres gained.

3. Climb high, sleep low. On rest days, walk up a few hundred metres and return to sleep.

4. Drink enough. Three to four litres of fluid a day.

5. Avoid alcohol and sleeping pills at altitude.

6. Eat, even without appetite. Carbohydrates are easiest.

7. Keep warm.

8. Never ascend with symptoms.

Standard itineraries on popular routes include the necessary rest days. Do not let anyone talk you into skipping them to save time.

About medication

Acetazolamide, sold as Diamox, speeds acclimatisation and is widely used both to prevent and to treat mild AMS. It is a prescription drug with side effects, including tingling fingers and frequent urination, and it is unsuitable for some people. Discuss it with a doctor before you travel and, if prescribed, know the dose. It does not mask symptoms, and it does not make a fast ascent safe.

The rules to remember

• If you feel unwell at altitude, assume it is altitude until proven otherwise.

• Never go higher with symptoms of AMS.

• If you are getting worse, go down.

• Never leave a sick person alone or send them down unaccompanied.

Speak up

Many people hide symptoms out of embarrassment or fear of holding back the group. Guides see this constantly. Tell your guide or companions how you feel each morning and evening, honestly. A day's delay costs little. Silence can cost a great deal.

Help on the trail

Volunteer doctors staff seasonal aid posts in the Everest region and at Manang on the Annapurna Circuit, and give free daily talks on altitude that are well worth attending. Helicopter evacuation is available from most trekking areas in good weather, which is why insurance covering rescue at the altitude of your trek is essential.

Perspective

Most trekkers experience nothing worse than a mild headache and a few restless nights. Altitude illness becomes dangerous mainly when people press on regardless. Walk slowly, rest when the schedule says so, listen to your body, and be willing to turn round. The mountain is not going anywhere.