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

High Altitude Sickness Prophylaxis

Acetazolamide 125-250 mg twice daily starting 24 hours before ascent is the recommended first-line prophylaxis for high altitude sickness. 1

Primary Prophylactic Measures

Non-Pharmacological Prevention

1. Gradual Acclimatization (First-line approach)
   • Ascend slowly at 300-600m/day above 2500m 1, 2
   • Include rest days (one day for every 600-1200m gained) 1
   • Pre-acclimatize by spending at least nine nights at altitudes >2500m within 30 days before ascent if rapid ascent is unavoidable 2
   • Maintain adequate hydration 1
   • Avoid overexertion 1

Pharmacological Prophylaxis

For General High Altitude Sickness Prevention:

• Acetazolamide:
  • Dosage: 125-250 mg twice daily 1
  • Timing: Start 24 hours before ascent 1
  • Duration: Continue during ascent and for 2-3 days at maximum altitude 3
  • Mechanism: Carbonic anhydrase inhibitor that increases ventilation and improves oxygenation 2
  • Particularly indicated when:
    • Rapid ascent is unavoidable (>300m/day) 2
    • Traveling to altitudes >3350m (11,000 feet) by air 3
    • Previous history of altitude sickness 4

For Those with History of High Altitude Pulmonary Edema (HAPE):

• Nifedipine:
  • Dosage: 20 mg extended-release every 8 hours 1, 2
  • Timing: Start one day before ascent 2
  • Duration: Continue during ascent and for 3-4 days after reaching final altitude 1
  • Mechanism: Vasodilator that decreases pulmonary artery pressure 2, 5

Contraindications and Special Considerations

Acetazolamide Contraindications:

• Kidney stones
• Sulfa allergy
• Severe hepatic or renal disease
• Adrenocortical insufficiency
• Hyperchloremic acidosis
• Sickle cell disease
• Aplastic anemia 1

Monitoring Requirements:

• Serum electrolytes
• Renal function
• Acid-base status 1

Population-Specific Considerations:

• Women: Higher risk of acute mountain sickness; consider iron supplementation 1
• Cardiovascular patients: Consult physician before high altitude travel; acetazolamide may reduce risk of subendocardial ischemia 1
• Hypertensive patients: Well-controlled hypertensive patients may reach very high altitudes (>4000m) with adequate therapy; uncontrolled/severe hypertensive patients should avoid high altitude exposure 6

Recognition and Management of Altitude Illness

Symptoms to Monitor:

• Mild to Moderate AMS: Headache, insomnia, anorexia, nausea, dizziness 7, 4
• Severe AMS: Vomiting, dyspnea, muscle weakness, peripheral edema 4
• HAPE: Incapacitating fatigue, chest tightness, dyspnea, dry cough progressing to pink frothy sputum 5
• HACE: Severe headache unresponsive to acetaminophen, ataxia, mental deterioration 5

Treatment:

• Immediate descent is the primary treatment for severe altitude illness 1
• Supplemental oxygen to maintain saturation >90% 1
• Dexamethasone for cerebral edema (not recommended for prophylaxis) 7, 4
• Nifedipine for treatment of HAPE 7, 5

Common Pitfalls and Caveats

• Don't rely solely on medications without proper acclimatization
• Don't ignore early symptoms of altitude sickness
• Don't continue ascent if symptoms develop
• Don't combine acetazolamide with other diuretics due to increased risk of dehydration and electrolyte imbalances 1
• Limit caffeine intake when taking acetazolamide to avoid enhanced side effects 1