Symptoms of altitude illness can begin at 8,000 ft (2,400 m) or lower, but serious altitude illness is rare below 10,000 ft (3,000 m). Symptoms occur because the body doesn't adapt well to having less oxygen at high altitude. At 18,000 ft (5,500 m) there is half the oxygen available at sea level, and on top of Mount Everest only a third.
The body adapts to lower oxygen mainly by breathing faster and deeper, and by raising the heart rate — both bring more oxygen to the body. Red cell numbers increase after two weeks or more at high altitude, which matters for people who live there. Individual susceptibility to altitude varies widely and seems to be genetically determined.
What happens to the body in altitude illness?
Lack of oxygen (hypoxia) causes fluid to leak and collect between cells in the brain and/or the lungs. Symptoms can be mild or severe.
Acute mountain sickness (AMS) — the mild form — causes headache, loss of appetite, nausea, fatigue, poor sleep and dizziness. These symptoms can resolve once you acclimatize, for example by spending one or two extra nights at the same altitude, or they may worsen and require descent.
AMS can progress to High Altitude Cerebral Edema (HACE): mental confusion and difficulty with balance and coordination. Hypoxia can also cause fluid to collect in the lungs — High Altitude Pulmonary Edema (HAPE): shortness of breath at rest, extreme fatigue, and a cough that is dry at first and later produces frothy or blood-tinged sputum.
HAPE and HACE are severe, often occur together in serious cases, and can be rapidly fatal if untreated. The treatment is descend, descend, descend.
Prevention
- A sensible itinerary is the most important way to avoid altitude illness. Above 10,000 ft (3,000 m), climb no more than 1,000 ft (300 m) a day. Where the terrain makes that impossible, take rest days — two are recommended at Namche Bazaar, since most itineraries gain 2,000 ft (600 m) in one day from Phakding. Build in one or two extra days so you can rest when you're unwell. It also helps to "climb high, sleep low".
- Diamox (acetazolamide) blocks an enzyme in the kidney, making the blood slightly acidic; the brain reads this as a signal to breathe more. It enhances the body's natural response to altitude and acts as a mild diuretic. Side effects include tingling of the fingers, toes and around the mouth. People with a severe sulfa allergy should not take it. The preventive dose is half a 250 mg tablet (125 mg) twice a day. Diamox will not mask the symptoms of altitude illness. Start it the day of, or the day before, ascending to 10,000 ft (3,000 m), continue through your ascent, and stop when you start descending.
- If you're allergic to sulfa drugs, dexamethasone (prescribed by a physician), a potent steroid, can be used preventively at 4 mg twice daily for a short period of 2–3 days during abrupt, unavoidable ascents.
- Other preventive strategies: pulmonary vasodilators such as nifedipine, a potent blood-pressure-lowering drug, can be used to prevent HAPE.
Treatment
Mild symptoms: stay at the same altitude and see whether symptoms resolve; ascend only once they have resolved completely. Diamox 250 mg two or three times a day can treat mild to moderate symptoms. If symptoms persist or worsen, descend.
Severe symptoms (HACE or HAPE): start descending immediately wherever feasible. Helicopter evacuation may be essential unless there is rapid improvement with treatment and walking down is possible. Physical exertion — even to descend — can be harmful in HAPE; severe HAPE patients should be carried down if a helicopter isn't available.
Treatments that help during descent:
- Diamox — one 250 mg tablet two or three times a day. Generally useful for mild to moderate AMS.
- Dexamethasone — a potent steroid, used temporarily in HACE to make descent possible. It improves symptoms without improving acclimatization; don't ascend while still taking it with symptoms. Dose: 8 mg initially, then 4 mg every 6 hours.
- Nifedipine — useful in HAPE: it lowers pressure in the lung's blood vessels, reducing fluid in the lungs. It also lowers blood pressure.
- Sildenafil (Viagra) or tadalafil may be useful in treating HAPE.
- Oxygen — very useful, particularly for HAPE.
Gamow or PAC bag
A portable bag that inflates into a pressure chamber. A person with severe HACE or HAPE is placed inside and air is pumped in with a foot pump; the higher pressure raises oxygen levels and the person can improve rapidly. It is used to get someone through an acute crisis until descent or helicopter evacuation is possible.
Bags are available at the Himalayan Rescue Association aid posts in Manang and Pheriche, at Khunde Hospital and at several other places in the Everest region. Many groups trekking to remote high-altitude areas now carry one; they can be rented in Kathmandu or overseas.
Three golden rules to avoid dying from altitude illness
- Learn to recognize the early symptoms of altitude illness, and be willing to admit you have them. You may be the only person in your group with symptoms.
- Never ascend to sleep at a new altitude with any symptoms of AMS.
- Descend if your symptoms get worse while resting at the same altitude.