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High-altitude disorders are due primarily to hypoxia; the rapidity and height of ascent influence the risk of occurrence.


Clinical Features

Acute mountain sickness (AMS) is usually seen in nonacclimated people making a rapid ascent to higher than 2000 m (6560 ft) above sea level. Symptoms resembling a hangover may develop within 6 hours after arrival at altitude but may be delayed as long as one day. Typical symptoms include bifrontal headache along with a combination of GI disturbance, dizziness, fatigue, or sleep disturbance. Worsening headache, vomiting, oliguria, dyspnea, and weakness indicate progression of AMS. Physical examination findings in early AMS are limited. Postural hypotension and peripheral and facial edema may occur. Localized rales are noted in up to 20% of cases. Funduscopy shows tortuous and dilated veins; retinal hemorrhages are common at altitudes higher than 5000 m (16,500 ft). Resting SaO2 is typically normal for altitude and correlates poorly with the diagnosis of AMS.

Diagnosis and Differential

The differential diagnosis includes hypothermia, carbon monoxide poisoning, pulmonary or central nervous system infections, migraine, dehydration, and exhaustion. The diagnosis is based largely on history of rapid ascent and symptoms.

Emergency Department Care and Disposition

The goals of treatment are to prevent progression, abort the illness, and improve acclimatization.

  1. Terminate further ascent until symptoms resolve. For mild AMS, symptomatic therapy includes an analgesic, such as acetaminophen or an NSAID, and an antiemetic, such as ondansetron disintegrating tablets, 4 to 8 mg every 4 to 6 hours PO. Mild AMS usually improves or resolves in 12 to 36 hours if ascent is stopped.

  2. A decrease in altitude of 300 to 1000 m should provide prompt relief of symptoms. Immediate descent and treatment are indicated for patients with moderate AMS or if there is a change in the level of consciousness, ataxia, or pulmonary edema.

  3. Low-flow oxygen also relieves symptoms.

  4. Consider hyperbaric therapy for moderate AMS if descent is not possible.

  5. Pharmacologic therapy for moderate AMS includes acetazolamide 125 to 250 mg in adults and 2.5 mg/kg in children, PO twice daily, until symptoms resolve and dexamethasone 4 mg PO, IM, or IV every 6 hours with a taper over several days.

    1. Indications for acetazolamide are (a) history of altitude illness, (b) abrupt ascent higher than 3000 m (9840 ft), (c) AMS, and (d) symptomatic periodic breathing during sleep at high altitude.

    2. Acetazolamide pharmacologically produces an acclimatization response by inducing a bicarbonate diuresis and metabolic acidosis. Acetazolamide is effective for both prophylaxis and treatment.

    3. Acetazolamide should be avoided in sulfa-allergic patients.

  6. Patients who respond well to treatment may be discharged. Provide counseling on preventing future episodes: graded ascent, prophylaxis using acetazolamide, and avoidance of overexertion, alcohol, and respiratory depressants. Begin prophylaxis with acetazolamide a day before ascent and continue for at least two days after reaching high altitude.

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