Daily Altitude Monitoring: Heart Rate, SpO2, Sleep, Gait
Altitude monitoring is not staring at one number. It is six readings taken the same way each day, read as a trend against your own baseline.
Log altitude, resting heart rate, SpO2, sleep, headache, appetite, gait and consciousness twice a day, under the same conditions. Your own trend matters far more than anyone else's numbers. A resting heart rate 10–20 bpm above your sea-level baseline is normal; a sustained rise plus headache, nausea or breathlessness is not. Unsteady walking or altered consciousness means descend now.
Most altitude mistakes are not measurement errors. They are interpretation errors: one low SpO2 reading in the evening, a number that looks alarming, a decision made without any trend behind it.
What to record, morning and evening
| Item | How |
|---|---|
| Camp altitude | Where you sleep tonight |
| Resting heart rate | 1 minute before getting up, or after 5 minutes seated |
| SpO2 | Same finger, warm hand, no nail polish; note the device |
| Sleep | Time to sleep, wake-ups, quality |
| Headache | 0–3 (none / mild / moderate / severe) |
| Appetite, nausea | Normal / reduced / nauseated / vomiting |
| Dizziness, fatigue | 0–3 |
| Cough, breathing | Dry cough / breathless on effort / breathless at rest |
| Gait | Can you walk a straight heel-to-toe line? |
| Consciousness | Alert / drowsy / confused / incoherent |
| Urine colour, intake | Dark / normal; rough fluid volume |
| Decision | Continue / hold / descend |
Heart rate
- At altitude, resting heart rate commonly runs 10–20 bpm above your sea-level baseline, with wide individual variation. That on its own is not altitude illness.
- Establish a baseline at home, then watch the trend. A sustained rise plus headache, nausea, fatigue or breathlessness means far more than any single reading.
- Caffeine, anxiety, pain, fever, medication (including beta-blockers) and fitness all shift the number. Do not delegate this to a watch.
- Very fast or irregular rate with chest pain, fainting or breathlessness at rest: stop ascending, treat as an emergency, descend.
- Avoid single-threshold rules like "above X bpm, turn around". Combine the number with symptoms and gait.
SpO2
- Normal SpO2 falls with altitude, and varies widely between people. A single low reading does not diagnose AMS or HAPE.
- Same device, same finger, warm hand, no nail polish, at rest. Read trends alongside symptoms.
- Cold extremities, poor circulation, nail polish and device error all push readings down. Oxygen makes the number look better without curing the illness.
- A clear drop plus breathlessness at rest, cough, or blue lips: treat as HAPE and descend or call for help.
Symptoms and the Lake Louise score
- The 2018 Lake Louise score: headache (0–3) plus at least one of gastrointestinal symptoms, fatigue, dizziness or poor sleep. A total of 3 or more, with recent ascent, suggests AMS.
- Ask the same questions at the same time each day. "Are you okay?" is not a question that produces useful answers.
- Mild AMS: stop ascending, rest, hydrate. If it worsens, descend.
- Gait: straight heel-to-toe walking. Unsteady, or needing support, is a HACE red flag — descend immediately.
- Consciousness: drowsiness, incoherence, or not waking normally is an emergency.
When a teammate is confused
Treat it as an emergency first: AVPU, breathing, warmth, glucose and temperature, then the HACE red flags of gait and consciousness. Do not wait for morning. See A confused teammate.
Red flags that do not need a number
- Breathless at rest, pink frothy sputum, blue lips → HAPE.
- Unsteady gait, altered consciousness, severe headache or vomiting → HACE.
- Chest pain, fainting, palpitations, one-sided weakness or slurred speech → emergency, descend.
- Any plan that involves "sleeping higher will fix it" is worse than staying put or going down.
Common mistakes
- Measuring SpO2 and ignoring symptoms and gait.
- One measurement instead of a trend.
- Applying someone else's normal values to yourself.
- Suppressing the numbers with oxygen or drugs, then continuing up.
- Collecting data and never making the continue / hold / descend decision.