Altitude and travel

How do you prevent altitude sickness?

By GyroscopeUpdated November 14, 20264 sources

Go up slowly, and count by where you sleep. Coming from low ground, keep the first night under 9,000 feet. Above 9,800 feet, sleep no more than 1,650 feet higher each night, and add an extra night for every 3,300 feet you climb.

What are the CDC’s pacing rules?

From the CDC’s travel guide, the Yellow Book, in its own numbers:

1. Don’t go from under 4,000 feet (1,200 m) to a sleeping elevation of 9,000 feet (2,750 m) or more in one day.
2. Once you’re above 9,800 feet (3,000 m), sleep no more than 1,650 feet (500 m) higher than the night before.
3. Add an extra night to adjust for every 3,300 feet (1,000 m) of sleeping elevation you gain.

Think of it as stairs with landings. Each step up is short, and every few steps you stop on a landing for a night before you climb again. The rules only count where you sleep, so a day hike above your bed doesn’t break them.

Why does going slow work?

Your body adjusts to thin air over days, and the CDC’s rules give it time to catch up. The air gets thin fast: by NASA’s model of the atmosphere, each breath at 9,000 feet carries about 72% of the oxygen it would at sea level, and at 10,000 feet the CDC puts it at 69%. Jump straight there and you’re asking for a lot in one night.

What else lowers the odds?

• No alcohol for the first 48 hours at high altitude, the CDC says. It also tells travelers not to use alcohol to help them sleep up high, because it slows breathing.
• A preventive medicine. The CDC names acetazolamide, which speeds up adjusting to altitude. It’s a prescription, so it’s a question for your doctor before the trip.
• A lower first stop. For Cusco and La Paz, the CDC says travelers can head down to places lower than the airport and sleep there for a night or two before going up (Cusco). For a Colorado ski week from sea level, the trip tool below suggests a night in Denver first.

Who’s most at risk?

The CDC’s risk table weighs three things: whether you’ve had altitude illness before, how high you sleep on the first night, and how fast you climb. In 3,158 adult visitors to Colorado resorts, people who lived below 3,000 feet were 3.5 times as likely to get altitude sickness and people who’d had it before 2.8 times. People under 60 were twice as likely as older visitors.

What if you get symptoms anyway?

Score yourself each morning with the Lake Louise check: headache, stomach, tiredness and dizziness, 0 to 3 each, after at least 6 hours up. 3 or more with a headache means altitude sickness (the symptoms). Then the CDC’s three rules: don’t go higher to sleep with symptoms, go down if they get worse, and going down about 1,000 feet usually helps fast.

The tool below takes your trip night by night and flags any night that breaks a rule, with the one change that fixes the most.