What is the recommended prophylaxis for high altitude (elevation) sickness?

High Altitude Prophylaxis Recommendations

The most effective prophylaxis for high altitude sickness is slow ascent (300-600 m/day above 2500 m) combined with acetazolamide at a dose of 125 mg twice daily, started 24-48 hours before ascent and continued for 2-3 days after arrival at the terminal altitude. 1

Primary Prevention Strategies

Non-Pharmacological Approaches

1. Gradual Ascent Protocol:

   • Maximum ascent rate of 300-600 m/day above 2500 m 1
   • Include a rest day for every 600-1200 m gained 1
   • Avoid vigorous physical exertion before acclimatization 1
   • Delay further elevation gain if symptoms appear 1

2. Behavioral Modifications:

   • Stay hydrated 1
   • Avoid alcohol and smoking 1
   • Avoid sleeping medications (can worsen sleep-disordered breathing at altitude)

Pharmacological Prophylaxis

1. First-line: Acetazolamide

   • Dosage: 125 mg twice daily 2
   • Timing: Start 24-48 hours before ascent 3, 4
   • Duration: Continue for 2-3 days after arrival at terminal altitude 1
   • Higher risk situations: For rapid ascent to >3500 m, consider 500-750 mg/day 4
   • Benefits: Reduces AMS incidence by approximately 48% 5
   • Mechanism: Induces metabolic acidosis, stimulates ventilation, improves oxygenation 3

2. Alternative: Dexamethasone (for those who cannot tolerate acetazolamide)

   • Dosage: 2 mg every 6 hours or 4 mg every 12 hours 1, 6
   • Military operations: 4 mg every 6 hours (with acetazolamide 125 mg twice daily) for rapid ascent above 11,500 ft 6
   • Benefits: Effective for prevention and may improve cognition and aerobic capacity 6

3. For specific populations:

   • Women: May benefit more from respiratory muscle training prior to altitude exposure 1
   • Patients with history of HAPE: Nifedipine (extended-release) recommended 1

Special Considerations

For Patients with Pre-existing Conditions

1. Cardiovascular disease:

   • Continue pre-existing medications at high altitude 1
   • Low-risk cardiac patients (CCS 0-I) may ascend to 4200 m with light-moderate exertion 1
   • Moderate-risk cardiac patients (CCS II-III) should limit ascent to 2500 m with only light exertion 1
   • High-risk cardiac patients (CCS IV) should not ascend to high altitude 1

2. Hypertension:

   • Well-controlled hypertensive patients may reach very high altitudes (>4000 m) with adequate therapy 1
   • Uncontrolled/severe hypertensive patients should avoid high altitude exposure 1

3. Ophthalmological concerns:

   • Monitor for high altitude retinopathy (typically asymptomatic) in those ascending beyond 4900 m 1
   • Be aware that acetazolamide may cause transient myopic shift 1

Recognition and Management of High Altitude Illness

High Altitude Pulmonary Edema (HAPE)

• Onset: Usually 2-4 days after rapid ascent
• Symptoms: Cough, exertional dyspnea, reduced exercise performance
• Treatment: Immediate descent to lower altitude and supplemental oxygen 1
• Pharmacological treatment: Nifedipine for those with history of HAPE 1

Common Pitfalls to Avoid

1. Inadequate preparation time: Starting acetazolamide only one day before ascent provides limited protection; begin at least 2 days before for optimal effect 3

2. Ignoring early symptoms: Delaying descent when symptoms appear can lead to severe illness

3. Overestimating fitness level: Even physically fit individuals can develop altitude sickness; fitness does not protect against altitude illness

4. Rapid ascent profiles: The most common preventable cause of altitude illness is ascending too quickly

5. Underestimating altitude thresholds: Risk increases significantly above 2500 m, with much higher risk above 3500 m 2

By following these recommendations, the risk of high altitude illness can be significantly reduced, allowing for safer travel to high altitude destinations.