Acute mountain sickness

Background

• Also referred to as AMS
• Usually only occurs with altitude >7000-8000ft
  • May occur at lower altitudes in patients who are particularly susceptible (COPD, CHF)
• Associated with rate of ascent, sleeping altitude, strength of hypoxic vent response
  • NOT associated with physical fitness, age, sex
• Tend to have recurrence of symptoms whenever they return to the symptomatic altitude

Clinical Features

• Onset
  • Symptoms usually develop 1-6hr after arrival at elevation
    • May be delayed for 1-2d
  • Especially common after the 1st or 2nd night's sleep
• Duration
  • Average duration of symptoms at 10,000ft = 15hr
  • At higher elevations symptoms may last weeks / more likely to progress to headacheCE

Differential Diagnosis

• Dehydration
  • AMS is not improved by fluid administration alone
  • Body hydration does not influence susceptibility to AMS
• Exhaustion
• Alcohol hangover
• Hypothermia
• CO poisoning
• CNS infection
• Migraine
  • Whereas supplemental O2 helps headache due to AMS in 10-15min, O2 has no effect on migraines
• TIA

High Altitude Illnesses

• Acute mountain sickness
• Chronic mountain sickness
• High altitude cerebral edema
• High altitude pulmonary edema
• High altitude peripheral edema
• High altitude retinopathy
• High altitude pharyngitis and bronchitis
• Ultraviolet keratitis

Evaluation

• Requires headache + 1 or more of the following:
  • Nausea, vomiting, or anorexia
  • Fatigue or weakness
  • Dizzy or lightheadedness
  • Difficulty sleeping
• Ataxia and confusion heralds onset of headacheCE

Management

Mild

1. Terminate ascent
   • Descend to lower altitude (by 1000-3000ft) OR acclimatize for 12-36hr at same altitude
2. Acetazolamide
   • Mechanism: speeds acclimatization by promoting bicarb diuresis
   • Indications:
     • History of altitude illness
     • Abrupt ascent to >9800ft
     • AMS requiring treatment
     • Bothersome periodic breathing during sleep
   • 125-250mg PO BID until symptoms resolve
   • Side-effects
     • Allergic reaction (if patient allergic to sulfa), paresthesias, polyuria, carbonated beverages taste bitter
3. Symptomatic treatment as necessary with analgesics and antiemetics
4. Sleep-agents
   • Benzos are only safe if given in conjunction with acetazolamide
   • Nonbenzos are safe (zolpidem, diphenhydramine)

Moderate-Severe

• Immediate descent for worsening symptoms
• Low-flow 0.5-1 L/min O2 if available (esp nocturnal administration)
• Acetazolamide 250mg PO BID
• Dexamethasone 4mg PO q6hr
  • Symptom-improvement only; unlike acetazolamide does not aid acclimatization
• Hyperbaric therapy

Prevention

• Graded ascent with adequate time for acclimatization is the best prevention
• Acetazolamide prophylaxis
  • Indicated for patients with history of altitude illness or forced rapid ascent to altitude
  • Start 24hr before ascent and continue for the first 2 days at altitude
  • Can be restarted if illness develops
  • Reduces symptoms of AMS by 75% in patients ascending rapidly to altitudes >8200ft
• Dexamethasone
  • Start day of ascent and continue for first 2 days at altitude
  • 4mg PO q12hr
  • Prevents and treats cerebral edema
• Ginkgo biloba
  • Controversial if effective; safe
• Ibuprofen
  • Prevention - less effective than acetazolamide, better than placebo
  • Treatment of headache

See Also

High Altitude Medicine