High Altitude Sickness

Aka: High Altitude Sickness, Acute Mountain Sickness

1. Epidemiology: Prevalence
   1. Colorado ski resort: 25% of travelers
   2. Himalayas: 50% of travelers
2. Background: Barometric Pressure
   1. Sea level: 760 mmHg
   2. Ski altitude (9-10,000 feet): 560 mmHg
   3. Kala Pattar (18,187 feet) : 375 mmHg
   4. Mount Everest (29,035 feet): 249 mmHg
3. Pathophysiology: Mechanism
   1. Hypobaric Hypoxemia results in paradoxical and maladaptive fluid retention
      1. Contrast with non-affected persons at altitude who experience diuresis
   2. Changes at altitude that may exacerbate comorbid illness
      1. Low partial pressure of oxygen
      2. Increased sympathetic tone
         1. Pulmonary artery Vasoconstriction
         2. Increased systemic vascular resistance
4. Risk Factors
   1. Rapid ascent
   2. Significant physical exertion
   3. Prior history of altitude sickness
   4. Traveling from low altitude
   5. Younger age
      1. Aside from comorbidity, older adults may be less affected by altitude
5. Contraindications: Comorbid Conditions
   1. Patients with asymptomatic cardiopulmonary disease may ascend safely to at least 8200 feet (2500 meters)
   2. Conditions which absolutely contraindicate high altitude travel
      1. Severe Chronic Obstructive Pulmonary Disease (COPD)
      2. Uncontrolled Congestive Heart Failure (CHF)
   3. Conditions for which caution should be Exercised due to risk of exascerbation (emphasize acclimitization)
      1. Arrhythmias
      2. Coronary Artery Disease
      3. Hypertension
      4. Sickle Cell Anemia (splenic infarct risk increases above 4900 feet (1500 meters)
         1. Keep Supplemental Oxygen available
6. Symptoms
   1. Common Symptoms
      1. Headache
      2. Malaise
      3. Anorexia
   2. Other Symptoms
      1. Fatigue
      2. Nausea or Vomiting
      3. Insomnia
      4. Dyspnea
      5. Dyspnea on Exertion
      6. Dry cough
      7. Irritable
      8. Decreased Urine Output
7. Course
   1. Onset: 6-12 hours following high altitude ascent
8. Diagnosis
   1. Headache and
   2. One or more of the following
      1. Fatigue or weakness
      2. Dizziness or light headedness
      3. Gastrointestinal distress (Nausea, Vomiting, Anorexia)
      4. Sleep disturbance
9. Differential Diagnosis
   1. Viral illness
   2. Hangover
   3. Exhaustion
   4. Dehydration
   5. Hypothermia
   6. Medication: Sedative or hypnotic
   7. Carbon Monoxide Poisoning
10. Management
    1. Very mild symptoms may resolve spontaneously with acclimitization
    2. Immediate descent (at least 1000 feet or 300 m) is most critical for moderate to severe symptoms
    3. Other measures for moderate to severe symptoms where descent is not immediately possible
       1. Supplemental Oxygen
       2. Acetazolamide 250 mg orally twice daily
       3. Dexamethasone 4 mg orally every 6 hours
       4. Gamow Bag (Portable Hyperbaric Chamber)
11. Complications (0.1 to 4 percent Incidence)
    1. See Pathophysiology above
    2. Altitudes above 11,400 feet (3500 meters) are associated with a more complicated course
    3. High Altitude Pulmonary Edema (HAPE)
    4. High Altitude Cerebral Edema (HACE)
12. Prevention
    1. Medication Prophylaxis
       1. Indications
          1. Travel to 11,000 feet in one day (or over 9,000 feet if history of prior altitude sickness)
       2. Acetazolamide (Diamox) 125 mg twice daily (FDA approved)
          1. Start 1 day or more before ascent
          2. Continue until acclimitization to the higheest sleeping altitude
          3. Up to 250 mg twice daily may be used (but 125 mg is typically sufficient)
       3. Dexamethasone 4 mg orally every 6-12 hours (not FDA approved)
          1. Alternative, in those who cannot take Acetazolamide
          2. Risk of rebound mountain sickness when discontinued
          3. Does not speed acclimitization, but does reduce symptoms
    2. General Pointers
       1. Recognize the symptoms of Acute Mountain Sickness
       2. Never ascend to sleep higher if you have symptoms
       3. Descend if symptoms do not resolve or worsen
       4. Never leave a person with altitude sickness alone
       5. Maintain hydration
       6. Avoid overexertion
       7. Avoid Alcohol and sedatives
       8. For altitudes above 9800 feet
          1. Do not sleep >2000 feet (600 meters) higher than the night before
          2. Spend an additional day if ascent over 2000 feet
13. References
    1. (2018) Presc Lett 25(2)
    2. Basnyat (2003) Lancet 361(9373): 1967-74 [PubMed]
    3. Fiore (2010) Am Fam Physician 82(9): 1103-10 [PubMed]
    4. Hackett (2001) N Engl J Med 345(2): 107-14 [PubMed]