How do you use a pulse oximeter on the Everest Base Camp trek?

Clip it on a warm finger after five minutes sitting still, read it before breakfast and before dinner from Kathmandu onward, and compare each reading with your own last few days, not with the 96% or more you see at home. Expect the number to fall as you climb and to recover slowly at each new altitude. The oximeter supports your judgment. It never overrules a headache.

What oxygen saturation is normal at each stop on the Everest Base Camp trek?#

Normal blood oxygen saturation, or SpO2, falls with altitude: lower than anything you see at home, and lower with each night higher. The air still holds 21% oxygen, but air pressure drops as you climb, and at about 5,500 m it is roughly half its sea-level value. Each breath delivers less oxygen to your lungs, and less reaches your blood. Above about 3,000 m, the oxygen in your blood falls onto the steep part of the oxygen-hemoglobin curve, where a small drop in pressure takes several points off the reading. Between sea level and 1,500 m the expected reading falls by only a few points. Between 2,500 m and 3,500 m it falls by about 8.

Luks and Hackett, in the New England Journal of Medicine in 2022, give the expected range for healthy people 24 to 48 hours after arriving at a given altitude. The table gives the lower edge of that range at each place you sleep, interpolated between the published altitudes and rounded down.

Which pulse oximeter should you buy for a high-altitude trek?#

Buy one with a published accuracy (ARMS) of 3% or lower, a signal-quality display such as a pulse waveform or quality light, and good tolerance of cold fingers and movement. ARMS measures how far a device's reading typically strays from an arterial blood sample. The US FDA's benchmark for fingertip devices is 3% or less. Put it, with a spare set of batteries, on your Everest Base Camp trek packing list.

Three features separate a useful oximeter from a toy:

• A signal-quality indicator. A perfusion index, a pleth (plethysmograph) waveform, or a proprietary quality mark tells you whether the number can be trusted. Without one, you are guessing.
• Low-perfusion and motion tolerance. Cold fingers at altitude have poor blood flow, which is when cheap sensors fail. A device validated for low perfusion earns its place.
• Independent test data. Before buying, check Open Oximetry, a UCSF-led project that lab-tests popular oximeters against arterial blood and publishes the results. It is the closest thing to an honest scoreboard for these devices.

The problem is where you will use it. Luks and Swenson, in High Altitude Medicine & Biology in 2011, found that accuracy declines below 80% saturation, which is where readings sit above Dingboche. Low-cost handheld devices match medical ones from 90% to 100% and lose accuracy below 90%. Devices are calibrated only down to 70%. Below that, the number is an extrapolation.

Skin tone matters too. Oximeters tend to overestimate saturation in people with darker skin, by about 2 points below 90% in the studies reviewed. In a 2024 UCSF study of 11 popular fingertip oximeters, only four had FDA 510(k) clearance, and five missed the 3% accuracy mark. The FDA's January 2025 draft guidance would raise validation studies from 10 to 150 participants with more skin-tone diversity.

HoneyGuide's Safety and Evacuation Protocol holds the oximeters our guides carry to three tests: FDA clearance, ARMS under 3%, and a signal-quality indicator.

A cheap oximeter is most reliable at sea level, where you do not need one.

How do you take an oximeter reading you can trust at altitude?#

Sit still for about five minutes, warm the finger, keep it motionless and shaded, and watch the display for two to three minutes before you write anything down. At altitude, small changes in breathing move the number a long way, so a single glance is not a reading.

1. Sit for five minutes first. Walking, talking and climbing the lodge stairs all lower the number for a while.
2. Warm the finger. Cold narrows the blood vessels in the fingers and lowers accuracy. Hold the hand in your armpit or put your gloves back on for a few minutes.
3. Keep still and breathe normally. Shivering and movement corrupt the signal. Deliberate deep breaths raise the number for a short while, which makes the reading look better than your night was.
4. Shade the sensor. Strong light can interfere with the reading, and so can nail polish.
5. Watch, then record. Wait for a steady waveform or a good quality light, watch for two to three minutes, and write down the value that appears most often.

Take readings away from the stove. Lodge dining rooms are heated by stoves burning yak dung and wood, and carbon monoxide makes a standard oximeter read higher than your true saturation.

Dünnwald and colleagues note that no uniform measuring protocol exists at altitude. That is the reason to fix your own routine: a reading only tells you something when it can be compared with the last one, taken the same way.

When should you take readings, and what should you write down?#

Twice a day, before breakfast and before dinner, starting in Kathmandu, and each time note the place, the reading, your pulse and how you feel. Kathmandu, at about 1,300 m, gives you a baseline before altitude changes it. The same two times each day make the readings comparable. HoneyGuide gives each traveler a booklet with space to record each reading.

Compare each morning with the evening before. When you sleep at the altitude you arrived at, the morning reading shows whether you have acclimatized a little overnight. Saturation climbs back over the days you spend at one altitude as your breathing adapts, so the morning reading is usually at or a little above the previous evening's. In one study in the Dünnwald review, the reading on the morning after arrival was about 3 points higher than on the evening of arrival. A morning reading below the evening before is the pattern worth noting. Check your symptoms, and compare again that evening.

Record your pulse as well. Resting heart rate rises on arrival at a new altitude and falls as you acclimatize, so it is a useful second line on the same page.

On the Everest Base Camp Trek and every other HoneyGuide trek, the guide takes these readings for each traveler before breakfast and before dinner from Kathmandu onward, logs them with the morning Lake Louise score, and sends them to HQ each evening, where the trend is checked across days. The idea is prevention. On a November 2021 trek over the Cho La, for example, Achal wrote that the group's guide, Rita Dorjee Sherpa, monitored them for altitude sickness and helped one member who fell ill early in the trip recover.

Which oximeter readings are warning signs?#

Three patterns deserve attention: saturation that is 5 points below what is standard at that altitude, saturation that fails to recover after a night or two at the same altitude, and any low reading that comes with symptoms. The pattern matters more than any single figure.

At a fixed altitude, saturation should rise over the following days as your breathing adapts. When it does not, the body is losing ground. There is no universal cut-off. Treat your SpO2 trend as an early warning, not a verdict. Signs and symptoms drive the key decisions.

Can an oximeter tell you whether you have altitude sickness?#

Not on its own. A 2024 systematic review by Goves and colleagues in Experimental Physiology covered seven studies of 1,406 people ascending to between 3,952 and 6,300 m. Falling saturation during ascent did predict who developed AMS, but ascent profiles and measurement methods varied so widely that no reliable test came out of it. Mallet and colleagues found only a weak to moderate link between saturation and Lake Louise scores in trekkers at 2,500 to 5,500 m. Ken Zafren, writing in Wilderness & Environmental Medicine in 2012, noted that oximetry flags many people who will get sick and many who will not.

So you can feel well at 75% or be ill at 88%. AMS is diagnosed by symptoms: a headache, with nausea, dizziness or fatigue, after arriving at a new altitude. Score those each morning, and let the score decide whether you go higher.

The exception is high-altitude pulmonary edema (HAPE), fluid on the lungs, and here the oximeter earns its place. The Wilderness Medical Society describes saturation lower than expected for the altitude as a key feature that separates HAPE from anxiety or ordinary breathlessness. The CDC Yellow Book puts a number on it: readings of 50% to 70% are common in HAPE, at least 10 points below healthy people at the same altitude. A very low reading together with breathlessness at rest, a cough or a gurgling chest means descend now, with someone beside you. Do not retake the reading in the hope of a better one.

Sources#

• Luks AM, Hackett PH. Medical Conditions and High-Altitude Travel. New England Journal of Medicine2022;386(4):364-373. Reprinted as Figure 3.5.1 in Hackett PH, Shlim DR, High-Altitude Travel and Altitude Illness, CDC Yellow Book 2026. The expected SpO2 range by altitude behind the table in section 1, and the rules for ascent and HAPE.
• Dünnwald T, Kienast R, Niederseer D, Burtscher M. The Use of Pulse Oximetry in the Assessment of Acclimatization to High Altitude. Sensors 2021;21(4):1263. The published SpO2 averages by altitude, the measuring routine, and the common errors at altitude.
• Luks AM, Swenson ER. Pulse oximetry at high altitude. High Altitude Medicine & Biology 2011;12(2):109-119. Why accuracy falls below 80% and how to read a device in the mountains.
• Goves JSL, Joyce KE, Broughton S, et al. Pulse oximetry for the prediction of acute mountain sickness: a systematic review. Experimental Physiology 2024;109(12):2057-2072. What the evidence does and does not say about predicting AMS.
• Luks AM, Beidleman BA, Freer L, et al. Wilderness Medical Society Clinical Practice Guidelines for the Prevention, Diagnosis, and Treatment of Acute Altitude Illness: 2024 Update. Wilderness & Environmental Medicine 2024. The ascent rules and the role of oximetry in recognizing HAPE.