What helps prevent high altitude sickness (Acute Mountain Sickness, AMS)?

Prevention of High Altitude Sickness (Acute Mountain Sickness)

The most effective prevention for high altitude sickness is slow ascent, with less than 400m/day above 2,500m altitude, and a rest day for every 600-1200m gained. 1

Primary Prevention Strategies

Non-Pharmacological Approaches

• Gradual ascent protocol:

  • Limit ascent to less than 400m/day when above 2,500m altitude
  • Include a rest day for every 600-1200m gained
  • Allow at least 2 days of acclimatization before engaging in strenuous exercise

• Lifestyle modifications during ascent:

  • Maintain proper hydration with adequate fluid intake
  • Avoid alcohol consumption
  • Follow a high-carbohydrate, low-fat, low-salt diet 2
  • Avoid intense exercise immediately upon arrival at altitude

Pharmacological Prevention

• First-line medication: Acetazolamide

  • Dosing: 125mg twice daily starting 24 hours before ascent 1
  • Higher doses (500-750mg/day) may be more effective for rapid ascents above 3,500m
  • Benefits include improved gas exchange, enhanced exercise performance, and reduced AMS symptoms 3, 4
  • Special populations: Provides additional benefit for blood pressure control in hypertensive patients 1

• Alternative medication: Dexamethasone

  • Can be used as short-term prevention when acetazolamide is contraindicated
  • Dosing: 4mg four times daily 3
  • Important limitation: Use should be restricted to 2-3 days due to side effects 1, 3
  • More valuable for treatment than prevention in most cases

Risk Factors to Consider

• Prior history of altitude sickness
• Low home elevation (living at sea level)
• Poor physical conditioning
• Rapid ascent profiles
• Higher maximum and sleeping altitudes
• Intense exercise upon arrival

Special Considerations

Gender-Specific Recommendations

• Women may benefit from:
  • Timing altitude exposure during the luteal phase of menstrual cycle (when hypoxic ventilatory response is higher)
  • Smaller increases in carbohydrate intake compared to men
  • Greater reduction in training intensity during chronic altitude exposure 1

Medical Conditions

• Cardiovascular conditions:

  • Well-controlled hypertensive patients may reach altitudes >4000m with adequate therapy
  • NYHA class I-II heart failure patients can travel to high altitudes if stable
  • NYHA class IV heart failure patients should avoid high altitude travel
  • Medication adjustments may be necessary (consult physician)

• Respiratory conditions:

  • Patients with severe COPD should be assessed before traveling to high altitudes
  • Children with congenital heart disease require special attention due to increased pulmonary vascular resistance at altitude

Treatment Considerations if Prevention Fails

• For High Altitude Pulmonary Edema (HAPE):

  • Nifedipine (20mg three times daily) may be used when descent is impossible 1
  • Oxygen therapy is crucial for serious cases 4

• For severe symptoms:

  • Immediate descent is the most effective intervention
  • Oxygen supplementation
  • For cerebral symptoms, dexamethasone may be effective 2

Common Pitfalls to Avoid

1. Rushing ascent profiles - The temptation to reach destinations quickly often leads to inadequate acclimatization
2. Underestimating individual susceptibility - Previous successful ascents don't guarantee future success
3. Delaying medication initiation - Acetazolamide should be started 24 hours before ascent, not after symptoms begin
4. Ignoring early warning signs - Headache, insomnia, anorexia, nausea, and dizziness should prompt immediate action
5. Relying solely on medications - Drugs complement but don't replace proper acclimatization protocols

Military experience has shown that proper use of acetazolamide prophylaxis results in fewer AMS symptoms and higher summit success rates, confirming its effectiveness as part of a comprehensive prevention strategy 5.