Last autumn, four people, two tourists and two Nepali porters, died of altitude sickness related complications in Khumbu and the Himalayan Rescue Association Aid Post at Pheriche carried out 36 helicopter evacuations. Every year, hundreds of trekkers fall victim to acute mountain sickness (AMS) which experts say can strike anywhere above 2,300 m, and sometimes even lower. With easy air travel and worldwide tourism, doctors say AMS incidence is more likely as harried lives don't allow people to ascend slowly, the best preventive measure for AMS, and people do too much too soon.

This is especially true for Nepal where one of the most popular treks, the Everest base-camp trek, starts from Lukla at 2,800 m. "There are very few places on earth that allow trekkers to saunter at over 4,000 m with sustained exposure to altitude without using crampons or ascenders," says Dr Buddha Basnyat, medical director for the Himalayan Rescue Association (HRA). "As a result, they don't realise the danger."

"It is 100 percent preventable. So it's a tragedy when someone dies from high altitude sickness," says Dr Basnyat. The HRA recommends an ascent of no more than 300 m every day above 3,000 m. In many cases, though, this advice is ignored. Even slow ascents need to be carefully managed-drinking three to four litres of fluid daily helps in the acclimatisation process.

A 1996 study of AMS conducted in Pheriche (4,243 m) showed that at least 30 percent of travellers had AMS. The symptoms-headaches and gastrointestinal troubles, or insomnia, dizziness and fatigue-fit the definition of AMS that was established in 1993. Two percent had High Altitude Cerebral Edema (HACE), a more malignant form of AMS that leads to fluid collection in the brain and is characterised by lack of muscular coordination, disorientation and vomiting. AMS can also lead to High Altitude Pulmonary Edema (HAPE)-fluid collection in the lungs.

The only cure is to descend immediately-people with AMS often have impaired judgement and may have to be forced to descend. A person with symptoms should never wait for medication or oxygen to take effect before descending. "If sick tourists arrive at the post in the morning it's possible to call for a helicopter evacuation. But if they arrive in the evening, we administer oxygen through a concentrator, or give them a session in the Gamow Bag, which simulates the higher pressure found at low altitudes." says Sanjay Tripathee, an HRA official who's spent many a night tending to sick patients in Pheriche. The Gamow Bag, and similar devices like the Portable Altitude Chamber and the Certec Caisson can save lives, and people going on long treks may want to consider carrying one. (See box for rental information in Kathmandu.)

Helicopter evacuations are a boon-but they're also expensive, and waiting to be evacuated at high altitude while suffering from AMS is inadvisable. Ignoring progressive symptoms of HACE can lead to death in as little as 12 hours, while even a descent of just 300-500 m helps in recovery. In any case, if you aren't near the HRA posts, then it's common to have a 24-hour wait before a helicopter arrives-first, you have to find a police post or national park post or local airport with radio facilities, get the message out to Kathmandu (to a friend, your trekking agency, or embassy), and have someone in the city, whether your agency or insurance firm, guarantee payment for the rescue flight ($800 an hour, $1,200-$2,000 for the whole flight).

There is a drug that hastens acclimatisation, Diamox, which the HRA sometimes recommends for symptoms of AMS, but the drug is a mild diuretic and causes dehydration, already a problem at high altitude. There are also drugs available for HACE and HAPE, but both have side effects which can themselves sometimes be fatal.

The HRA posts at Manang (3,500 m) and Pheriche are both equipped with an oxygen concentrator, and a Gamow Bag each. They also hold video screenings about the dangers of AMS for locals and trekkers. "I think a lot of people are still not aware about AMS. They've never seen anyone get sick. So they don't think it's a danger," says Dr Barbara Dahl, a volunteer medic who will be working at the post in Pheriche this spring. "A friend of mine, a nurse from California, spent a week of her ski vacation in Colorado in a hospital."

Even in the mountains of Colorado, situated at a relatively low 3,000 m, an estimated 15-40 percent of vacationers fall victim to mountain sickness. Their complaints are as minor and transient as headaches and loss of appetite, and as serious as disorientation and difficulty in breathing. Dr Dahl says the basic tenet of the HRA, is as applicable to Colorado as it is to Nepal is: "Never ascend with mild symptoms of AMS. And if they get worse, descend," she says.

Mountain sickness is basically caused by lack of oxygen-the medical term is hypoxia-caused by the decrease in atmospheric pressure. It is generally believed that the effect of hypoxia on the brain causes most of the symptoms people experience. One theory holds that the chemical messages whizzing constantly around the brain are altered, but this doesn't explain why blood capillaries start to leak and fluid accumulates in the brain or the lungs.

Doctors who've worked in high-altitude clinics the world over are unanimous on one thing: fitness, age and gender have little to do with mountain sickness. Fatigue, dehydration, hunger, low blood sugar, quick ascents, and exertion after that, all heighten the risk of AMS. "This means that Nepalis are as susceptible to AMS as foreign trekkers are," says Dr Basnyat. "There's a term in Sanskrit dum giri, dum meaning 'breath' and giri meaning 'mountain', and a term in Nepali lek laagnuu. These show that AMS is known even among the local population."

Dr Basnyat believes that as many as a third of all porters suffer from AMS. What makes prevention even more important is that most people, including high-risk groups like porters and pilgrims, don't have insurance for helicopter evacuation in medical emergencies. "Unlike tourists, they may be slower to complain about AMS and thus jeopardise their life for fear of losing their jobs," says Dr Basnyat.

In fact, it was the death of a porter in 1997 on the Thorong La, two hours above the HRA post in Manang, that catalysed the formation of the International Porter Protection Group (IPPG) to lobby and encourage Nepali and foreign trekking agencies, and their leaders and trekking guides, to provide a minimum standard of care for porters. "Lowland porters are just as susceptible to AMS as western trekkers, but also much more likely to develop hypothermia and frostbite," says Dr Jim Duff, a high-altitude medic and HRA volunteer who is behind the IPPG. "Over the years it is interesting to speculate just how many porters have died or been maimed in the trekking industry, and just how many of these deaths were preventable."