DISORDERS CAUSED BY ALTITUDE - Medicine for Mountaineering and Other Wilderness Activities - page 351

fluid is absorbed as fast as it forms, but if not, HAPE or the exercise equivalent begins.
The evolution of interstitial to alveolar edema is caused by rapid ascent, particularly when
associated with strenuous exercise.
Forreasonsthatarenotunderstood,somewellacclimatizedhigh-altituderesidents,even
though not unusually susceptible, develop HAPE when they return to altitude after a week
or ten days near sea level. Such reentry HAPE is most frequent in children.
The incidence of HAPE and HACE varies with geographical conditions. A climber liv-
ing in Seattle can be up and down Mount Rainier (14,410 feet or 4400 m) in a weekend.
Since that climber will be climbing fast, AMS is likely—the incidence is over 50 per-
cent—but a fast descent is possible if symptoms become bad. On Denali (Mount McKin-
ley), which is much larger and higher (20,300 feet or 6200 m), deep snow, heavier packs,
severe weather, and longer distances not only demand greater work but also increase the
likelihood of HAPE and HACE and make rapid descent to safety much harder. The risk of
developing HAPE after a rapid ascent to 12,000 feet (3700 m) is about one in two hundred
(0.5 percent) in adults—higher in children.
The diagnosis of HAPE depends on a history of rapid ascent, often with strenuous ex-
ertion, and on the signs and symptoms described above. High-altitude pulmonary edema
may progress very rapidly, particularly during the night. Any worsening of the condition
demands prompt descent.
The most important treatment is getting down to a lower altitude, either by evacuation
or by treatment with a portable hyperbaric chamber. If the individual cannot walk, he or
she must be carried. Since exercise can make HAPE worse, the ill person should not be al-
lowedtocarryapackandshouldbeallowedtowalkdownonlyoneasyterrain.Descentof
as little as 2000 to 3000 feet (600 to 900 m) often results in prompt relief. The speed with
which individuals can recover from HAPE is remarkable.
If oxygen is available, it should be given without delay. Rescue parties should bring
oxygen or a portable hyperbaric chamber if the person cannot be moved, for example if a
major injury is present. Deaths have occurred when the seriously ill person has worked too
hard during evacuation.
Most cases of HAPE occurring below 15,000 feet (4600 m) and possibly higher can be
treatedusingaportablehyperbaricchamberwithoutevacuationifpulseoximetry(theabil-
ity to measure the saturation of oxygen in the blood) is available. If the oxygen saturation
can be maintained above 90 percent, the individual can be treated with multiple chamber
sessions. The head of the chamber should be raised because fluids pool in the lungs and a
person lying flat has trouble breathing. In some cases, additional oxygen must be provided
inside the chamber to keep the oxygen saturation high enough. A number of different pro-
tocols have been suggested. One protocol that works is to treat the person in the chamber
for hour-long sessions, with brief respites (five to ten minutes) out of the chamber between