Upon reaching a height over 2500 m above sea level symptoms of altitude illness can develop over 1 – 5 days. The risk is mainly ­determined by the altitude and rate of ascent and the symptoms vary. Most common are symptoms of acute mountain sickness (AMS) but more dangerous high altitude cerebral edema (HACE) and high altitude pulmonary edema (HAPE) can also develop. The causes of AMS, HACE and HAPE are lack of oxygen and insufficient acclimatization, but the presenting form is determined by the responses of the body to the lack of oxygen. The most common symptoms of AMS include headache, fatique and nausea, but insomnia and nausea are also common. The most common symptoms of HAPE are breathlessness and lassitude whereas the cardinal sign of HACE is ataxia, but confusion and loss of consciousness can also develop. In this article all three main forms of altitude illness are reviewed. The emphasis is on preventive measures and treatment but new knowledge on pathogenesis is also addressed.

Table I .  Symptoms and signs of high-altitude illness.

Table II. Lake Louise Acute Mountain Sickness Score (ref 22).

Table III. Risk categories for high altitude illness. Based on reference 7.

Table IV. Drugs for prevention and treatment of high altitude illness. Based on reference 7.

Figure I. World highest areas. Figure: Guðbjörg Tómasdóttir.

Figure II. La Paz is the capital of Bolivia and the highest capital in the world, at 3650 m, where many tourist experience high altitude illness.

Figure III.  A graph showing reduced air pressure with increasing altitude. Figure: Guðbjörg Tómasdóttir.

Figure IV. A graph showing reduced arterial oxygen saturation with increasing altitude of mountain climbers on Mt Everest. The figure is based on ref. 71 and slightly modified.

Figure V. A group of backcountry skiers climb Sveinsgnípa (1925 m) with Hvannadalshnjúkur, the highest mountain in Iceland, in the background, 2110 m. Photo: Ólafur Már Björnsson.

Figure VI. The symptoms of high altitude illness overlap considerably as their pathophysiology except that the pathophysiology of high altitude pulmonary edema is a bit different from high altitude illness and high altitude cerebral edema. With the permission of Mike Grocott.
Design: Guðbjörg Tómasdóttir.