Acute Mountain Sickness

Epidemiology

High Altitude is Defined as >8000 ft Elevation (see High Altitude)

  • Clinically Important Mountain Sickness Generally Does Not Occur Below Altitude of 8000 ft
  • Incidence of Mountain Sickness is Almost 50% at >15,000 ft

Risk Factors for Acute Mountain Sickness

  • Age <46 y/o
    • Possible Risk Factor
  • Extreme Cold
  • Female Sex
    • Possible Risk Factor
  • History of Acute Acute Mountain Sickness (Med Sci Sports Exerc, 2002) [MEDLINE]
  • History of Migraines (see Migraines) (Am J Respir Crit Care Med, 2012) [MEDLINE]
    • Possible Risk Factor
  • Individual Susceptibility
    • Decreased Risk of Acute Mountain Sickness in Those who Urinate More at High Altitude
    • Increased Risk of Acute Mountain Sickness in Those with Blunted Respiratory Response to Hypoxia
      • Increased Risk is Observed in Those with Ventilatory Response to Hypoxia at Exercise <0.78 L/min/kg (Am J Respir Crit Care Med, 2012) [MEDLINE]
    • Increased Risk of Acute Mountain Sickness in Those with Desaturation at Exercise in Hypoxia at Least 22% (Am J Respir Crit Care Med, 2012) [MEDLINE]
  • Lack of Previous Acclimatization: <5 days above 3000 m in the preceding 2 mo (Med Sci Sports Exerc, 2002) [MEDLINE]
  • Rapid Rate of Ascent
    • Ascent >400 m/day (Am J Respir Crit Care Med, 2012) [MEDLINE]
    • Ascent >625 m/day Above 2000 m (Med Sci Sports Exerc, 2002) [MEDLINE]
  • Underlying Lung Disease

Factors Not Associated with Protection Against Acute Mountain Sickness

  • Physical Fitness

Physiology

  • High Altitude with Inadequate Acclimatization
    • Acute Mountain Sickness and High-Altitude Cerebral Edema (HACE) Represent Different Points Along a Spectrum of Disease (see High-Altitude Cerebral Edema)

Clinical Manifestations

General Comments

  • Onset
    • Symptoms May Start within 6-8 hrs, But Usually Occur at 48 hrs After Arrival to Altitude
  • Exercise May Exacerbate Symptomatology

Gastrointestinal Manifestations

Neurologic Manifestations

  • Asthenia/Generalized Weakness (see Asthenia)
  • Dizziness (see Dizziness)
  • Fatigue (see Fatigue)
  • Headache (see Headache)
    • Epidemiology
      • Headache is a Hallmark Symptom
  • Insomnia/Difficulty Sleeping (see Insomnia)
  • Malaise

Pulmonary Manifestations

Other Manifestations


Prevention of Acute Mountain Sickness

General Measures

  • Avoid Ethanol and Respiratory Depressants (see Ethanol)
  • Avoid Extreme Cold
  • Maintain Hydration
  • Graded Ascent (For Planned Final Altitude >3000 m): ascent rate of 300-500 m/day with rest q3-4 days
    • An Ascent Made After 1 wk at an Altitude of >2000 m (as Compared with an Ascent from Near Sea Level) Decreases Both the Incidence and Severity of Acute Mountain Sickness at 4300 m by 50% (High Alt Med Biol, 2009) [MEDLINE]

Risk Assessment (NEJM, 2013) [MEDLINE]

  • Low Risk
    • Slow Ascent <500 m/day Above 2500 m
    • No History of Acute Mountain Sickness/High-Altitude Cerebral Edema/High-Altitude Pulmonary Edema
    • Rapid Ascent (>500 m/day in Person Partially Acclimatized (At Altitude <3000 m in Preceding Weeks)
  • Medium Risk
    • Unknown History of Acute Mountain Sickness/High-Altitude Cerebral Edema/High-Altitude Pulmonary Edema and Fast Ascent (>500 m/day Above 3000 m)
    • Unknown History of Acute Mountain Sickness/High-Altitude Cerebral Edema/High-Altitude Pulmonary Edema and Rapid Ascent (Ascent to >3000 m in 1 Day)
  • High Risk
    • Unknown History of Acute Mountain Sickness/High-Altitude Cerebral Edema/High-Altitude Pulmonary Edema Very Rapid Ascent (Considerably >500 m/day), and High Final Altitude (>4000 m)
    • History of Acute Mountain Sickness/High-Altitude Cerebral Edema/High-Altitude Pulmonary Edema with Previous Exposure to High Altitude That is Similar to Planned Final Altitude

Nonsteroidal Anti-Inflammatory Drugs (NSAID) (see Nonsteroidal Anti-Inflammatory Drug)

  • Acetylsalicylic Acid (Aspirin) (see Acetylsalicylic Acid): decreases risk of acute mountain sickness-related headache
    • Administration: 320 mg PO q4hrs starting 1 hr before ascent to altitudes between 3480-4920 m
  • Ibuprofen (Advil, Brufen, Motrin, Nurofen) (see Ibuprofen)
    • Ibuprofen Decreases the Risk of Acute Mountain Sickness-Related Headache
    • Administration: 600 mg PO TID starting a few hrs before ascent to altitudes between 3480-4920 m

Acetazolamide (Diamox) (see Acetazolamide)

  • Pharmacology
    • Causes Hyperchloremic Metabolic Acidosis, Which Stimulates Ventilation, Mimicking the Acclimatization Process
  • Indications
    • Moderate-High Risk of Acute Mountain Sickness
  • Administration
    • Oral: 125-250 mg PO BID beginning 1-2 days before ascent
    • Discontinue After 2 days at Final Altitude
  • Clinical Efficacy
    • Acetazolamide Decreases the Relative Risk of Severe High Altitude-Related Illness by 44% (Am J Respir Crit Care Med, 2012) [MEDLINE]

Dexamethasone (Decadron) (see Dexamethasone)

  • Indications
    • Moderate-High Risk of Acute Mountain Sickness
  • Administration
    • Oral: 4 mg PO BID-TID
  • Clinical Efficacy
    • Second-Line Agent
    • May Be Used if Acetazolamide is Not Tolerated

Treatment of Acute Mountain Sickness

Mild-Moderate Acute Mountain Sickness

  • Day of Rest
    • Indicated for Mild-Moderate Acute Mountain Sickness: symptoms usually resolve with 1-2 days (with proper management)
  • Descend to 500-1000 m
    • If No Improvement with a Day of Rest
  • Acetazolamide (Diamox) (see Acetazolamide)
    • Administration
      • Oral: 125-250 mg PO BID
  • Antiemetics
    • May Be Used as Required
  • Nonsteroidal Anti-Inflammatory Drugs (NSAID) (see Nonsteroidal Anti-Inflammatory Drug)
  • Voluntary Hyperventilation
  • Re-Ascent May Be Possible After Recovery is Complete
    • Consider Acetazolamide 250 mg PO BID During Re-Ascent

Severe Acute Mountain Sickness

  • Descend as Soon as Possible
  • Oxygen (see Oxygen)
    • May Be Used with Hyperbaric Bag
  • Hyperbaric (Gamow) Bag
    • Rationale
      • Rebreathing Bag into Which the Victim is Placed (with Foot-Pedal Pressurization)
  • Dexamethasone (Decadron) (see Dexamethasone)
    • Administration
      • Oral: 4 mg PO BID-TID
      • IV: 4 mg PO BID-TID
      • IM: 4 mg PO BID-TID

References

  • Acute mountain sickness susceptibility, fitness and hypoxic ventilatory response. Eur Respir J 1991;4:1000-1003 [MEDLINE]
  • Acute mountain sickness: influence of susceptibility, pre-exposure and ascent rate. Med Sci Sports Exerc 2002;34:1886-1891 [MEDLINE]
  • Effect of six days of staging on physiologic adjustments and acute mountain sickness during ascent to 4300 meters. High Alt Med Biol 2009;10:253-60 [MEDLINE]
  • Physiologic risk factors of severe high altitude illness: a prospective cohort study. Am J Respir Crit Care Med 2012;185:192-198 [MEDLINE]
  • Acute high-altitude illnesses. N Engl J Med 2013;368:2294-2302 [MEDLINE]