Acute mountain sickness

Background

1. Usually only occurs with altitude >7000-8000ft
   1. May occur at lower altitudes in pts who are particularly susceptible (COPD, CHF)
2. Associated w/ rate of ascent, sleeping altitude, strength of hypoxic vent response
   1. NOT associated with physical fitness, age, sex
3. Pts tend to have recurrence of symptoms whenever they return to the symptomatic altitude

Clinical Features

1. Onset
   1. Symptoms usually develop 1-6hr after arrival at elevation
      1. May be delayed for 1-2d
   2. Especially common after the 1st or 2nd night's sleep
2. Duration
   1. Average duration of symptoms at 10,000ft = 15hr
   2. At higher elevations symptoms may last weeks / more likely to progress to HACE
3. Diagnosis
   1. Requires HA + 1 or more of the following:
      1. Nausea, vomiting, or anorexia
      2. Fatigue or weakness
      3. Dizzy or lightheadedness
      4. Difficulty sleeping
4. Ataxia and confusion heralds onset of HACE

DDX

1. Dehydration
   1. AMS is not improved by fluid administration alone
   2. Body hydration does not influence susceptibility to AMS
2. Exhaustion
3. Alcohol hangover
4. Hypothermia
5. CO poisoning
6. CNS infection
7. Migraine
   1. Whereas supplemental O2 helps HA due to AMS in 10-15min, O2 has no effect on migraines
8. TIA

Treatment

1. Mild AMS
   1. Terminate ascent
      1. Descend to lower altitude (by 1000-3000ft) OR acclimatize for 12-36hr at same altitude
   2. Acetazolamide
      1. Mechanism: speeds acclimatization by promoting bicarb diuresis
      2. Indications:
         1. History of altitude illness
         2. Abrupt ascent to >9800ft
         3. AMS requiring treatment
         4. Bothersome periodic breathing during sleep
      3. 125-250mg PO BID until symptoms resolve
      4. Side-effects
         1. Allergic reaction (if pt allergic to sulfa), paresthesias, polyuria
   3. Symptomatic treatment as necessary w/ analgesics and antiemetics
   4. Sleep-agents
      1. Benzos are only safe if given in conjunction with acetazolamide
      2. Nonbenzos are safe (zolpidem, diphenhydramine)
2. Moderate-Severe AMS
   1. Immediate descent for worsening symptoms
   2. Low-flow 0.5-1 L/min O2 if available (esp nocturnal administration)
   3. Acetazolamide 250mg PO BID
   4. Dexamethasone 4mg PO q6hr
      1. Symptom-improvement only; unlike acetazolamide does not aid acclimatization
   5. Hyperbaric therapy

Prevention

1. Graded ascent w/ adequate time for acclimatization is the best prevention
2. Acetazolamide prophylaxis
   1. Indicated for pts w/ history of altitude illness or forced rapid ascent to altitude
   2. Start 24hr before ascent and continue for the first 2d at altitude
   3. Can be restarted if illness develops
   4. Reduces symptoms of AMS by 75% in pts ascending rapidly to altitudes >8200ft
3. Dexamethasone
   1. Start day of ascent and continue for first 2d at altitude
   2. 4mg PO q12hr
   3. Prevents and treats cerebral edema
4. Ginkgo biloba
   1. Controversial if effective; safe

See Also

High Altitude Medicine

Source

Tintinalli