High altitude standard definitions and associated physiological changes
| Altitude | Physiology | |
|---|---|---|
| Intermediate altitude | 1500–2500 m | Physiological changes occur, SpO2 >90%, altitude illness possible but rare |
| High altitude | 2500–3500 m | Altitude illness common with rapid ascent |
| Very high altitude | 3500–5800 m | Altitude illness common, SpO2 <90%, marked hypoxia with exercise |
| Extreme altitude | >5800 m | Marked hypoxia at rest, progressive deterioration, permanent survival not possible |