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- Incidence dependent on:
- Rate of ascent
- Final altitude
- Sleeping altitude
- Duration at altitude
- Acute mountain sickness (AMS) incidence:
- Up to 67% incidence with rapid ascent (1–2 days) to >14,000 ft
- 22% incidence for skiers visiting resorts and sleeping at 7,000–9,000 ft, 40% at 10,000 ft
- AMS risk factors:
- Previous history of high-altitude illness
- Physical exertion
- Younger persons (<50 yr)
- Physical fitness not protective
- Obesity and existing lung disease increase the risk
- High-altitude pulmonary edema (HAPE) incidence:
- Varies with rate of ascent
- High-altitude cerebral edema (HACE) incidence <1%
- HACE and HAPE are unusual at altitudes under 13,000 ft (4000 m)
- Relationship between pregnancy and high-altitude illness is not clearly established.
- Pregnancy-induced hypertension, proteinuria, and peripheral edema are more common at high altitude, which may be related to maternal hypoxemia.
- No evidence of increase in spontaneous abortions, placental abruption, or placenta previa at high altitudes
- Travel by pregnant women with normal pregnancies to moderate altitudes appears safe, although caution should be exercised when traveling >13,000 ft and for women with complicated pregnancies
Although elderly persons are more likely to have underlying health problems that may be affected by altitude, such as HTN, COPD, and coronary artery disease, the risk of development of AMS is less in those older than 55 than in other age groups.
- Rapid ascent to >8,000 ft (about 2,500 m) without proper acclimatization is the most common cause of high-altitude–related illness.
- Rapidity of ascent, final altitude reached, sleeping altitude, and individual susceptibility all play a role in development of high-altitude illness as well.