At 4,000 m normal resting oxygen saturation is between 83% and 90%, typically around 87%. In San Pedro de Atacama (2,400 m) expect 90% to 96%, at El Tatio (4,300 m) 81% to 89% and on the summit of Cerro Toco (5,604 m) 72% to 82%. Readings rise about 2 points after 5 days of acclimatization and drop 2 to 4 points while you sleep.
What SpO₂ measures and why it drops with altitude
SpO₂ is the percentage of hemoglobin carrying oxygen in your blood. A pulse oximeter estimates it by shining light through your finger. As you climb, air pressure drops and each breath brings less oxygen into the lungs (see our altitude to oxygen calculator). Saturation falls with it, but not linearly: up to about 2,500 m the hemoglobin curve cushions the drop, and above 3,000 m every 500 m of elevation takes off 2 to 3 points.
Reference table: normal resting SpO₂ by altitude
Values for healthy lowlanders, awake and at rest, on day 3 to 5 at altitude. The first number in the range is the lowest value we still consider normal.
| Location | Altitude | Normal SpO₂ range | Typical | Arrival (48 h) | Acclimatized (5+ days) |
|---|---|---|---|---|---|
| Sea level | 0 m | 95% - 100% | 98% | 98% | 98% |
| San Pedro de Atacama | 2,400 m | 90% - 96% | 93% | 93% | 93% |
| Cusco | 3,400 m | 86% - 92% | 89% | 87% | 91% |
| La Paz | 3,640 m | 84% - 91% | 88% | 86% | 90% |
| Reference altitude | 4,000 m | 83% - 90% | 87% | 85% | 89% |
| El Tatio Geysers | 4,300 m | 81% - 89% | 86% | 84% | 88% |
| Cerro Toco summit | 5,604 m | 72% - 82% | 77% | 75% | 79% |
| Licancabur summit | 5,916 m | 71% - 81% | 76% | 74% | 78% |
| Ojos del Salado summit | 6,893 m | 64% - 76% | 71% | 69% | 73% |
| Everest summit (no O₂) | 8,848 m | 48% - 65% | 57% | 55% | 59% |
Above 5,500 m readings are almost always taken during effort or after a short pause, so values at the low end of the range are normal.
How to measure correctly with a pulse oximeter
- Sit for 5 minutes before measuring and warm your hand if it is cold.
- Use a finger without nail polish, with your hand still and at heart level.
- Wait about 30 seconds for the number to settle and log that value along with your pulse.
- Measure at the same time every day, ideally on waking, to compare your trend.
A finger pulse oximeter weighs about 50 grams and runs on AAA batteries. Bring spares, since cold nights at altitude drain them fast.
What to do with your reading
Saturation alone does not decide whether you keep climbing. In the field we combine trend and symptoms. If your reading is below range and you have symptoms, do not sleep higher that day. If it gets worse with symptoms, descend. To plan how much height to gain each night use the acclimatization rate calculator, and if you are coming to Atacama, read our acclimatization itinerary in San Pedro de Atacama.
How we use pulse oximeters on our Atacama expeditions
On every climb of peaks such as Cerro Toco (5,604 m), Láscar Volcano (5,592 m) or Licancabur (5,916 m) we measure the group's saturation on waking and before sleep. The number shows each person's trend; we decide whether to go up or down by looking at symptoms too.
Cold hands, nail polish or having just walked lower the reading by several points. We measure seated, after 5 minutes of rest with a warm hand, and log the stable value. What worries us is saturation that drops day after day at the same altitude, even if it is still within range.
We have seen people at 4,500 m feeling fine at 80% and others at 86% with a severe headache. If SpO₂ falls below 75% at that altitude together with a headache that won't go away, resting pulse above 110 bpm or breathlessness at rest, we descend.
Frequently Asked Questions about Oxygen Saturation at Altitude
What is normal oxygen saturation at 4,000 meters?
At rest and awake, between 83% and 90%, typically 87%. During the first 48 hours it can be 2 points lower, and after 5 days of acclimatization it is usually around 89%.
What saturation is normal in San Pedro de Atacama, Cusco or La Paz?
In San Pedro de Atacama (2,400 m) 90% to 96% is normal. In Cusco (3,400 m) 86% to 92% and in La Paz (3,640 m) 84% to 91%. It is common to sit at the low end of the range during the first two days.
What oxygen saturation is dangerous at altitude?
There is no single threshold because it depends on altitude. As a guide, a reading more than 5 points below the normal range for your altitude, or below 75% between 4,000 and 5,000 m, together with symptoms such as persistent headache, breathlessness at rest or confusion, is a reason to descend.
Why does saturation drop at night?
Breathing slows during sleep and pauses appear, especially during the first days at altitude. Night-time SpO₂ 2 to 4 points below daytime values is normal, so always compare readings taken at the same time of day.
Can a pulse oximeter tell me if I have altitude sickness?
It helps but does not diagnose it. Acute mountain sickness is assessed by symptoms (headache plus nausea, fatigue, dizziness or poor sleep). The oximeter is useful for tracking your trend during acclimatization and spotting drops outside the expected range.
