CHAPTER 39 • ENVIRONMENTAL INJURIES 237the initial pathologic changes. Days later, cerebral
edema, pulmonary hypertension, and alveolar leakage
lead to death if untreated.- Maximal oxygen uptake(VO2max) falls 10% for each
3281 ft of altitude gained over 5000 ft (Hackett and
Roach, 2001a). VO2maxat sea level is notpredictive of
performance at altitude. Many of the world’s elite
mountaineers have average sea level VO2maxvalues
(Hackett and Roach, 2001b). Past performance and
personal problems with altitude illness are the best
predictors of future performance and the need for
aggressive preventive interventions.
DIFFERENTIAL DIAGNOSIS
•Any of the symptoms of AMS on ascent past 8000 ft
should trigger suspicion for altitude illness. Key differ-
ential diagnostic considerations include dehydration,
hypothermia and a viral infection. Dehydration can be
differentiated by response to a fluid challenge.
Hypothermia can be distinguished by a low core tem-
perature and improvement with exertion/increased
body temperature. Altitude illness worsens with exer-
tion. Although viral syndromes have similar symptoms,
they are typically accompanied by fever, myalgia, or
diarrhea and are more subacute in onset than AMS.
Dyspnea at rest, worsening of symptoms after sleep-
ing, and gait disturbance point toward altitude illness.
Abnormal tandem gait is a sensitive examination find-
ing for severe AMS progressing to HACE.
Improvement with descent confirms the diagnosis.
TREATMENT
- Initial field treatment involves stopping the ascent and
rest. A lack of improvement in 12 h should lead to a
descent in altitude. Typically, descending 1000–3000 ft
is sufficient. Acetazolamide (125 to 250 mg bid)
should be given. If available, low flow oxygen, and
portable hyperbaric bags are helpful. Additional
useful medications are ibuprofen or aspirin for
headache and promethazine (25–50 mg) or prochlor-
perazine (5–10 mg) for nausea and vomiting.
•Treatment of HACE or HAPE should include imme-
diatedescent and evacuation. Dexamethasone (4 mg
po/IM q 6 h) for HACE and nifedipine (10 mg po
once followed by 30 mg of the extended release tablet
bid) should be instituted for HAPE (level of evidence
B, nonrandomized clinical trial) (Bartsch et al, 1991). - Hospital treatment will also include high flow oxygen
or hyperbaric oxygen, and loop diuretics for pulmonary
edema. Mechanical ventilation is only required in cases
of coma.
PREVENTION- Altitude illness can be prevented by proper acclimati-
zation. Physiologic changes of hyperventilation, tachy-
cardia, erythropoesis, and a variety of cellular changes
take from minutes to months to reach their peak.
Recommendations for the prevention of altitude illness
are provided in Table 39-5 (Hackett and Roach, 2001b).
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345:107–114, 2001a.TABLE 39-5 Prevention of Altitude Illness- Begin exertion below 8,000 ft. Spend two to three nights sleeping
between 8000 and 10,000 ft before ascending above 10,000 ft. - Sleep no more than 1500 ft higher each day above 10,000 ft.
- Avoid alcohol or sedatives.
- Avoid dehydration or hypothermia.
- Consider acetazolamide 250 mg po bid beginning the day before
ascent: for any individual with a prior history of AMS, when
climbing above 11,400 ft., or when acclimatization is not possible.
(Continue until after 48 h at maximum altitude.) - In the face of symptoms of AMS—do not go higher. Descend if
symptoms do not improve in 12 h. - Reserve dexamethasone for the treatment of severe AMS or HACE.