Altitude sickness should “never be fatal by definition,” says Dr. Ken Zafren, meaning it’s like chickenpox—unpleasant and discomforting, but rarely life-threatening.

Yet it can be, adds the mountain and wilderness medical expert, if ignored. And it often is ignored, by hearty trekkers or climbers who play by the motto, “no pain, no gain.” A better motto might be that of the Himalayan Rescue Association, where Zafren, an ex-climber and vociferous trekker himself, has been associate director since 1992: “Don’t go Too High, Too Fast.”

The HRA, which has run clinics near Everest Base Camp in Nepal since the 1970s, mostly to prevent and treat altitude sickness in foreign travellers, still notes a few people die from the more severe forms every year. And while that’s out of the thousands who arrive there, the HRA now reports that the rates of serious altitude sickness, and death, are on the rise as more inexperienced trekkers venture out.

Education is the key. Decades of science have produced cocktails and protocols to prevent and treat it—but not getting it in the first place is easy, and still considered the best course of action.

The 3 Types of Altitude Sickness

  • Acute Mountain sickness (AMs) Also common name for general altitude sickness. 1,900 to 2,900 metres. Symptoms: rapid breathing, headache, dizziness, nausea, sleeplessness; usually abates, if stay at same altitude for a day.
  • High Altitude pulmonary edema (hApe) Fluid fills in lungs; can occur at 3,000+ metres. Symptoms: difficulty breathing (especially lying down), chest pain, undue fatigue, coughing; can be fatal, needs immediate medical care and descent.
  • High Altitude Cerebral edema (hACe) Causes excessive fluid in brain, swelling of brain; can occur at 3000+ metres. Symptoms: confusion, lack of coordination, hallucinations, unable to walk heel-to-toe; extremely dangerous, can be fatal, requires immediate descent and medical care.

Best Prevention: Acclimatization

Defined as gradual ascent: lets body adjust to decreased levels of oxygen in air and blood at each elevation you reach. Drink lots of water, avoid alcohol, heavy meals after ascent, over-exertion.

Definition of Altitude Sickness

Illness brought on by lack of oxygen and decreased barometric pressure in the air at higher elevations; ranges from mild to serious to sometimes fatal.


  • Absolute best cure is descent: go down immediately, if symptoms are prolonged or serious, and if possible.
  • Painkillers for headache.
  • For serious cases needing on-site care: oxygen from portable supply; or portable hyperbaric oxygen bag.

The International Society of Mountain Medicine says:

Ascend slowly means: spend 1 night at intermediate elevation below 3,000 metres. Above this level, don’t ascend more than 300-500 metres per day; you can trek higher during day, but you must go down to lower elevation overnight. For every 1,000 metres, spend two nights at same elevation.

Q&A with Dr. Zafren

Outpost: How often is altitude sickness a problem for trekkers and travellers in places like Nepal?

Zafren: The overall incidence in trekkers passing through Pheriche [a village in Nepal where HRA runs a clinic] on the way to Everest Base Camp is about 35 percent. Over half of trekkers flying to Lukla [common starting point for Everest trekkers] for the first time have AMS by 4,300 metres…On Denali the incidence of AMS is 30 percent overall at 4,300 metres, and also increases at the higher camps.

OP: It’s generally reported that getting AMS is often determined by individual susceptibility–can you comment? Do factors like being healthy, fit or younger play a role?

Z: The chances of getting AMS are most directly related to the rate of ascent…The best way to find out how susceptible [you’re] likely to be is to make a test trip prior to departure for a major trek or expedition. It is possible to measure how much one’s breathing increases in response to low levels of inspired oxygen, measured in pulmonary function labs, but this is only somewhat correlated [to getting AMS.] Being healthy and fit are probably risk factors for AMS, because physically fit people have a tendency to ascend too rapidly. Being young is a risk factor, probably for the same reason.

OP: What are common mistakes of trekkers that contribute to AMS?

Z: The mistakes are not following the Golden Rules of Altitude, which I learned as a volunteer for the HRA many years ago. 1) Symptoms at altitude are due to the altitude, unless proven otherwise. 2) Don’t ascend if you have symptoms. 3) If symptoms are severe or getting worse, go down—anyone with altered mental status or difficulty walking heel-to-toe must be helped to descend immediately. 4) Never send anyone with altitude illness down alone. All mistakes fall into these categories, and if everyone followed these rules there would probably never be a death from altitude illness. Being a member of a trekking group increases the risk of death because of pressures to not delay the group.

OP: What is HRA’s position on preventive medication for AMS? When would someone travelling to a high altitude know if this is appropriate?

Z: We recommend against routine use of prophylaxis for AMS…Exceptions are those who know they’re susceptible, or those who cannot avoid rapid ascent—rare situations in rescue or flights to high altitude destinations with no chance to acclimatize.

OP: I’ve also heard it’s better to walk to higher elevations, if possible, than to fly or drive. What’s your take on this?

Z: It’s not clear if passive ascent–—lying or driving—is a problem, but it is clear that AMS is more likely to affect those who go too high too fast, and flying or driving makes it easier to do this.

OP: Many people think AMS is only a concern of extreme adventures. But is it also a concern for more moderate adventure treks or trips?

Z: AMS is a concern for any altitude above 2,500 metres or so–lower for some people. A few people with underlying lung problems have even had HAPE at 2,500 metres. I’ve studied AMS and HAPE in Colorado, where there are many cases of both at resorts located in the 2,500-3,000 metre range, even in normal people without any known predisposing factors.

OP: What was one of the more memorable cases of AMS you encountered in Nepal, and how was it resolved?

Z: I took care of a man on Denali…who had HAPE, and I sent him down with a guide in the morning. [He] was fine in the morning, felt a bit unwell about noon when I examined him, but had no signs of HACE. A few hours later he staggered down to the ranger camp and collapsed in front of the medical tent. In spite of my treatment with oxygen and dexamethasone, he was nearly comatose on the arrival of the helicopter, fortunately about an hour later. He woke up as the helicopter descended below 3,000 metres and was essentially normal when it landed in Talkeetna (essentially sea level). I have spent many long nights at Pheriche helping to pump the [hyperbaric] Gamow Bag for hours. All of the patients with HAPE or HACE who arrive conscious at Pheriche seem to survive, but often with a lot of supportive care.

Note: The information in this article is intended as a general guideline only, and in no way should replace a proper consultation with a doctor, or at a travel clinic. Always get individualized medical advice before travelling.

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