Acute mountain sickness

Background

  • Also referred to as AMS
  • Usually only occurs with altitude >7,000-8,000ft (2,000 m)
    • May occur at lower altitudes in patients who are particularly susceptible (COPD, CHF, obesity, history of AMS)
  • Development of symptoms based on: rate of ascent, sleeping altitude, strength of hypoxic ventilatory response, alcohol intake, obesity
    • NOT based on physical fitness, age, sex, smoking, previous high-altitude experience
  • Tend to have recurrence of symptoms whenever they return to the symptomatic altitude
  • Low partial pressure of O2 leads to decreased diffusion of O2 across alveolar spaces -> hypoxemia results in tachypnea and cerebral vasodilation (↓ CO2) -> increased ICP

Clinical Features

  • Lake Louise Consensus Definition [1]
    • An Individual is at or above 2500 m (~8000 ft) above sea level and
    • A headache is present and:
    • An Individual has any one of the following:
  • 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

High Altitude Illnesses

Evaluation

  • Clinical diagnosis
  • Mental status, cerebellar exam - rule out HACE
  • Lung exam - rule out HAPE
  • Lake Louise Scoring System: Sum of symptoms 0-3 (none, mild, moderate, severe/incapacitating). Mild corresponds to score 3-4, Moderate-severe corresponds to score ≥5
    • Headache
    • Gastrointestinal symptoms
    • Fatigue/weakness
    • Lightheadedness
    • Difficulty Sleeping

Expected SpO2 and PaO2 levels at altitude[2]

Altitude SpO2 PaO2 (mm Hg)
1,500 to 3,500 m (4,900 to 11,500 ft) about 90% 55-75
3,500 to 5,500 m (11,500 to 18,000 ft) 75-85% 40-60
5,500 to 8,850 m (18,000 to 29,000 ft) 58-75% 28-40

Management

High altitude management algorithm.

Mild

  • Terminate ascent and/or descend [3]
    • Descend to lower altitude of 300-500m (1000-3000ft) OR acclimatize for 12-36hr at same altitude
  • Acetazolamide
    • Mechanism: speeds acclimatization by promoting bicarb diuresis -> metabolic acidosis -> ↑ ventilation
    • 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
      • Can also worsen dehydration by promoting bicarb diuresis
  • Symptomatic treatment as necessary with analgesics (NSAIDs) and antiemetics (ondansetron)
  • Sleep-agents

Moderate-Severe

  • Immediate descent of 500 m (~ 1500 ft) for worsening symptoms
  • Low-flow 0.5-1 L/min O2 if available (especially nocturnal administration)
  • Acetazolamide 250mg PO BID
  • Dexamethasone 4mg PO q6hr
    • Symptom-improvement only; unlike acetazolamide does not aid acclimatization
  • Portable hyperbaric chamber
    • Useful in conditions which do not allow descent (ie blizzard, avalanche)
    • Simulate descent to 3000-8000ft


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 125 mg PO BID 24hr before ascent and continue for the first 48hrs at peak altitude
    • Can be restarted if illness develops
    • Reduces symptoms of AMS by 75% in patients ascending rapidly to altitudes >8200ft
  • Dexamethasone[4]
    • Start day of ascent and continue for first 2 days at altitude
    • 4mg PO q12hr
    • Prevents and treats cerebral edema
  • Combination acetazolamide and dexamethasone
  • 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)


Medication Dosing

Acetazolamide 125-250mg BID PO — Continue until symptoms resolve; caution in sulfa allergy Acetazolamide 250mg BID PO Dexamethasone 4mg q6hr PO

Disposition

  • Most patients are treated symptomatically and managed as outpatients
  • If other high altitude illnesses are considered, consider further work-up and/or observation

See Also

References

  1. ↑ Maggiorini M, Müller A, Hofstetter D, Bärtsch P, Oelz O. Assessment of acute mountain sickness by different score protocols in the Swiss Alps. Aviat Space Environ Med. 1998;69(12):1186-1192.
  2. ↑ Gallagher, MD, Scott A.; Hackett, MD, Peter (August 28, 2018). "High altitude pulmonary edema". UpToDate. Retrieved May 2, 2019.
  3. ↑ 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.
  4. ↑ Luks AM, McIntosh SE, Grissom CK, et al. Wilderness Medical Society Practice Guidelines for the Prevention and Treatment of Acute Altitude Illness: 2014 Update. Wilderness & Environmental Medicine. 2014(25): S4–S14)
  5. ↑ Bernhard WN, Schalick LM, Delaney PA, Bernhard TM, Barnas GM. Acetazolamide plus low-dose dexamethasone is better than acetazolamide alone to ameliorate symptoms of acute mountain sickness. Aviat Space Environ Med. 1998;69(9):883-886.
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