High-Altitude Travel & Altitude Illness

Environments significantly above sea level expose travelers to cold, low humidity, increased ultraviolet radiation, and decreased air pressure, all of which can cause problems. The biggest concern, however, is hypoxia. At an elevation of 10,000 ft (3,000 m) above sea level, for example, the inspired PO₂ is a little more than two-thirds (69%) what it is at sea level. The magnitude of hypoxic stress depends on elevation, rate of ascent, and duration of exposure. Sleeping at high elevation produces the most hypoxemia; day trips to high elevations with return to low elevation are much less stressful on the body. Typical high-elevation destinations include Cusco (11,000 ft; 3,300 m), La Paz (12,000 ft; 3,640 m), Lhasa (12,100 ft; 3,650 m), Everest Base Camp (17,700 ft; 5,400 m), and Kilimanjaro (19,341 ft; 5,895 m; see Chapter 10, Tanzania: Kilimanjaro).

The human body adjusts very well to moderate hypoxia, but requires time to do so (Box 3-5). The process of acute acclimatization to high elevation takes 3–5 days; therefore, acclimatizing for a few days at 8,000–9,000 ft (2,500–2,750 m) before proceeding to a higher elevation is ideal. Acclimatization prevents altitude illness, improves sleep and cognition, and increases comfort and well-being, although exercise performance will always be reduced compared to what it would be at lower elevations. Increase in ventilation is the most important factor in acute acclimatization; therefore, respiratory depressants must be avoided. Expanded red-cell production does not play a role in acute acclimatization, although hemoglobin concentration is increased within 48 hours because of diuresis and decreased plasma volume.