Acute Mountain Sickness

Epidemiology

  • High Altitude: (see High Altitude, [[High Altitude]]) defined as >8000 ft elevation
    • Clinically important mountain sickness generally does not occur below 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 [MEDLINE]
  • History of Migraines (see Migraines, [[Migraines]]) [MEDLINE]: possible risk factor
  • Individual Susceptibility
    • Decreased Risk in Those who Urinate More at High Altitude
    • Increased Risk in Those with Blunted Respiratory Response to Hypoxia: increased risk is observed in those with ventilatory response to hypoxia at exercise less than 0.78 L/min/kg [MEDLINE]
    • Increased Risk in Those with Desaturation at Exercise in Hypoxia at Least 22% [MEDLINE]
  • Lack of Previous Acclimatization: <5 days above 3000 m in the preceding 2 mo [MEDLINE]
  • Rapid Rate of Ascent
    • Ascent >400 m/day [MEDLINE]
    • Ascent >625 m/day Above 2000 m [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, [[High-Altitude Cerebral Edema]])

Diagnosis

Arterial Blood Gas (ABG) (see Arterial Blood Gas, [[Arterial Blood Gas]])

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Chest X-Ray (CXR) (see Chest X-Ray, [[Chest X-Ray]])

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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
  • Effect of Exercise: may exacerbate symptomatology

Gastrointestinal Manifestations

  • Anorexia (see Anorexia, [[Anorexia]])
  • Nausea/Vomiting (see Nausea and Vomiting, [[Nausea and Vomiting]]): presence of vomiting likely indicates progression of acute mountain sickness to high-altitude cerebral edema (HACE) (see High-Altitude Cerebral Edema, [[High-Altitude Cerebral Edema]])

Neurologic Manifestations

  • Asthenia/Generalized Weakness (see Asthenia, [[Asthenia]])
  • Dizziness (see Dizziness, [[Dizziness]])
  • Fatigue (see Fatigue, [[Fatigue]])
  • Headache (see Headache, [[Headache]]): hallmark symptom
  • Insomnia/Difficulty Sleeping (see Insomnia, [[Insomnia]])
  • Malaise

Pulmonary Manifestations

  • Dyspnea (see Dyspnea, [[Dyspnea]])

Other Manifestations

Prevention of Acute Mountain Sickness

General Measures

  • Avoid Ethanol and Respiratory Depressants (see Ethanol, [[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 at least 2000 m (as compared with an ascent from near sea level) reduces both the incidence and severity of acute mountain sickness at 4300 m by 50% [MEDLINE]

Risk Assessment [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

Non-Steroidal Anti-Inflammatory Drugs (NSAID) (see Non-Steroidal Anti-Inflammatory Drugs)

  • Acetylsalicylic Acid (Aspirin) (see Acetylsalicylic Acid, [[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 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

  • Administration: 125-250 mg PO BID beginning 1-2 days before ascent,

    discontinue after 2 days at final altitude

  • Clinical Efficacy: acetazolamide reduces the relative risk of severe high altitude-related illness by 44% [MEDLINE]

Dexamethasone (Decadron) (see Dexamethasone)

  • Indications: moderate-high risk
  • Administration: 4 mg PO BID-TID
  • Clinical Efficacy: second-line agent, 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: 125-250 mg PO BID
  • Antiemetics: as required
  • Non-Steroidal Anti-Inflammatory Drugs (NSAID) (see Non-Steroidal Anti-Inflammatory Drugs)
  • Voluntary Hyperventilation
  • Re-Ascent: possible after recovery is complete
    • Consider acetazolamide 250 mg PO BID during re-ascent

Severe Acute Mountain Sickness

  • Descent: as soon as possible
  • Oxygen (see Oxygen): may be used with hyperbaric bag
  • Hyperbaric/Gamow Bag
    • Rationale: rebreathing bag into which victim is placed (with foot-pedal pressurization)
  • Dexamethasone (Decadron) (see Dexamethasone)
    • Administration: 4 mg PO BID-TID (or IV, IM)

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]