Going up to a high plateau, climb by sleeping altitude (how high you sleep that night) and go down if symptoms get worse; don't tough it out

In a real emergency, call 911 first, then read this.

Cost

One or two extra days for acclimatization. Preventive medicine is prescription-only, so ask a doctor before you leave. The hard part is being willing to keep these days free when the schedule is tight.

What you get

Sleeping above 2,450 meters carries a risk of altitude sickness. High-altitude cerebral edema and pulmonary edema (fluid in the brain and lungs) can kill if you don't descend to lower ground in time. The U.S. Centers for Disease Control and Prevention's Yellow Book gives three rules for preventing severe illness: know the early symptoms and be willing to admit them; with symptoms, however mild, do not go to sleep any higher; and if symptoms keep getting worse after rest or treatment at the same altitude, descend. Acute altitude sickness usually improves quickly after descending 300 meters or more. For high-altitude cerebral edema in a remote area, descend at once, and if dexamethasone and oxygen are available, use them together. For high-altitude pulmonary edema, in most cases you must descend at once, and descending and oxygen are both far more effective than medicine

Notes

What counts is "how high you sleep," not how high you went during the day. If you have symptoms, don't sleep any higher; if they get worse after rest, go down. An unsteady walk, a change in consciousness, or shortness of breath even at rest may be cerebral or pulmonary edema, and in the wild you must descend at once. Medicine is no match for descending and oxygen.

Evidence grade

A : Specific numbers from meta-analyses, large cohorts or randomized trials; for law and policy, the statute or official text.

Sources

1. US Centers for Disease Control and Prevention. Yellow Book: High-Altitude Travel and Altitude Illness: "Any unacclimatized traveler proceeding to a sleeping altitude of ≥2,450 m (≥8,000 ft)—and sometimes lower—is at risk for altitude illness"
2. Rate of ascent: "500 m (1,650 ft) per night in sleeping altitude once above 3,000 m (9,800 ft)", plus one acclimatization day for every 1000 m of ascent
3. Acetazolamide for prevention: "125 mg twice a day; 250 mg twice a day if >100 kg body weight"
4. Descent is required: "If symptoms become worse despite rest or treatment at the same elevation"
5. "Never ascend to sleep at a higher altitude when experiencing symptoms of altitude illness, no matter how minor the symptoms seem" "AMS improves rapidly with a descent of 300 m (1,000 ft) or more" "In remote areas, initiate descent for anyone suspected of having HACE" "Descent and oxygen are much more effective treatments than medication". https://www.cdc.gov/yellow-book/hcp/environmental-hazards-risks/high-altitude-travel-and-altitude-illness.html
6. Wilderness Medical Society (2024). Clinical Practice Guidelines for the Prevention, Diagnosis, and Treatment of Acute Altitude Illness: 2024 Update. Wilderness & Environmental Medicine. https://doi.org/10.1016/j.wem.2023.05.013

Translated from the Chinese original. Original book, section 13, tip 33. Content may be out of date and rules differ by place. When you actually deal with an agency, a doctor or a court, follow what local officials, doctors and lawyers tell you. Disclaimer