Everest Three Passes Altitude Sickness: AMS Prevention & Safety

How Real Is the Altitude Risk?

Altitude sickness is the single biggest risk on the Everest Three Passes trek, and the risk is more sustained than on the classic Everest Base Camp trek. You spend many nights above 4,000 m and several around or above 5,000 m, and top out at roughly 5,545 m at Kala Patthar and Gokyo Ri, with Kongma La at 5,535 m. Up there you breathe roughly half the oxygen available at sea level, and acute mountain sickness (AMS) can affect anyone, regardless of age or fitness.

What makes this trek harder on the body is that the altitude barely lets up through the middle of the circuit, three big passes back to back, with little chance to drop low and recover. That is why the standard itinerary keeps the two mandatory acclimatisation days at Namche and Dingboche, plus natural rest at Chukhung and Gokyo.

Three Passes altitude profile

AMS Symptoms: Mild vs Emergency

Know the difference. Mild AMS is common up high and manageable; the severe forms, HACE (brain) and HAPE (lungs), are life-threatening and demand immediate descent.

The golden rule: if you have symptoms, do not go higher, and above all never cross a pass while feeling unwell, a crossing only adds altitude, exposure and hours from help. If symptoms are severe or worsening, descend immediately, even at night. Descent is the cure. Tell your guide honestly about any symptoms.

How to Prevent AMS

• Never skip the acclimatisation days at Namche and Dingboche, and use the natural rest at Chukhung and Gokyo. Follow "climb high, sleep low".
• Ascend slowly. Above 3,000 m, aim to raise your sleeping altitude by no more than about 300-500 m per day, the built-in itinerary respects this.
• Hydrate. Drink 3-4 litres a day, and treat your own water so you keep drinking freely over the long trek.
• Walk slowly and steadily, "pole, pole" (slowly, slowly). Let your breathing set the pace, especially on pass climbs.
• Avoid alcohol and sleeping pills at altitude; they suppress breathing. Eat well even without appetite, carbohydrates aid acclimatisation.
• Consider Diamox (acetazolamide) if your doctor advises it. A common preventive dose is 125 mg twice daily, started a day before going high; it speeds acclimatisation. It is a prescription drug, discuss it with your doctor first, and it is no substitute for sensible ascent.
• Do not cross a pass ill. If you are unwell at a pass base such as Chukhung, Dzongla or Gokyo, rest or reverse rather than committing to the crossing.

The Icy Pass Crossings

The three passes add a layer of hazard on top of altitude, and the two combine badly, you are at your most exposed exactly where the air is thinnest.

• Cross only in good, settled weather, starting very early to be over the top before afternoon cloud and wind build. Be willing to wait a day or reverse.
• Icy ground. Cho La crosses a small glacier where the ground is often icy and a slip is consequential, carry microspikes (and an ice axe in snowy conditions). Kongma La and Renjo La can also be icy after snow.
• Long, remote days. There are no teahouses on the passes, so a problem high on a pass is hours from shelter, another reason to turn back early if the weather or your health is off.
• Cold and wind. The passes are high and exposed; frostbite and hypothermia are real risks, dress for it and keep moving.

See the difficulty guide for the terrain and the best time guide for when the passes are safest.

Cold, Insurance & Emergency Action

Beyond altitude, plan for the other high-Khumbu hazards and for rescue:

• Extreme cold and the Khumbu cough. Nights at the high villages and the pre-dawn pass starts drop far below freezing; a proper down jacket and a -15 C sleeping bag (see packing list) are safety items. The dry, thin air commonly triggers a persistent cough, a buff and hydration help.
• Carry travel insurance with helicopter-evacuation cover valid for trekking to at least 5,600 m. This is non-negotiable, a heli rescue from a high pass can cost many thousands of dollars, and standard policies often exclude high-altitude activity, so check the wording.
• Keep your insurer's emergency number and policy number accessible, and with your guide.
• If someone shows emergency symptoms, descend immediately while arranging help, losing altitude is the priority, not waiting for a helicopter.
• There are aid posts on the trail, notably the Himalayan Rescue Association clinic at Pheriche, which can assess and treat altitude illness; your guide will know where they are.