Epidemiology

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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)

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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

• Anorexia (see Anorexia)
• Nausea/Vomiting (see Nausea and Vomiting)
  • Presence of Vomiting Likely Indicates Progression of Acute Mountain sickness to High-Altitude Cerebral Edema (HACE) (see High-Altitude Cerebral Edema)

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

• Dyspnea (see Dyspnea)

Other Manifestations

• Peripheral Edema (see Peripheral Edema)

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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

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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

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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]