Acute mountain sickness

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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)
  • Development of symptoms based on: rate of ascent, sleeping altitude, strength of hypoxic ventilator response
    • NOT based on physical fitness, age, sex
  • Tend to have recurrence of symptoms whenever they return to the symptomatic altitude

Clinical Features

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

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 headache

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
  • Hypoglycemia

High Altitude Illnesses

Evaluation

  • Clinical diagnosis

Management

Mild

  • Terminate ascent and/or descend [2]
    • Descend to lower altitude (by 1000-3000ft) OR acclimatize for 12-36hr at same altitude
  • 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
  • Symptomatic treatment as necessary with analgesics and antiemetics
  • Sleep-agents
    • Benzos are only safe if given in conjunction with acetazolamide
    • Nonbenzodiazepines 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 (however, important to consider that taking ibuprofen may mask symptoms)

Disposition

See Also

References

  1. Schneider M et al. Acute mountain sickness: Influence of susceptibility, preexposure, and ascent rate. Med Sci Sports Exerc 2002; 34:1886-1891.
  2. Luks A, McIntosh S, Grissom C, Auerbach P, Rodway G, Schoene R, Zafren K, Hackett P. Wilderness Medical Society Practice Guidelines for the Prevention and Treatment of Acute Altitude Illness: 2014 Update. Wilderness Environ Med. 2014; S4-S14.