The kidneys sense the higher pH levels, and begin the process of pulling bicarbonate from the blood. Occasionally, fluid accumulates more rapidly than the body can absorb it. Pulmonary or cerebral edema can be fatal. Clinical studies have shown that at an altitude of 14000 feet, 0.5 percent of adults and 8 percent of children under age 16 will suffer from pulmonary edema. Males and females are equally affected.
Early symptoms are weakness, disorientation, irrational behavior and hallucinations.
Although individuals unaccustomed to high altitude may experience more distress than those who have become acclimatized, this is not always the case. Non-acclimatized individuals may experience AMS early on, but more serious problems are unlikely to arise until after several days of exposure. Individuals who are already acclimatized are at risk for unusual and potentially lethal fluid accumulation in the lungs if they descend to sea level and then return rapidly to the summit. In effect, they lose their acclimatization and may not realize it. Any abrupt change in symptoms should be taken as a warning sign that AMS may be accelerating toward one of these more dangerous conditions.