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
- 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
Pulmonary Manifestations
- Dyspnea (see Dyspnea, [[Dyspnea]])
Other Manifestations
- Peripheral Edema (see Peripheral Edema, [[Peripheral Edema]])
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]