Altitude Sickness — Prevention and Treatment for Travelers
Altitude sickness — also called acute mountain sickness (AMS) — affects up to 75% of travelers above 3,500 m and can strike anyone regardless of age, fitness, or previous altitude experience. It is caused by reduced oxygen pressure at high elevations and can progress to life-threatening conditions if ignored. The good news: it is almost entirely preventable with proper acclimatization.
Types of Altitude Illness
Acute Mountain Sickness (AMS) — The mildest and most common form. Symptoms: headache (the cardinal symptom), nausea, fatigue, dizziness, poor appetite, and disturbed sleep. Onset: 6–12 hours after arrival at altitude. Most cases resolve within 24–48 hours if you stop ascending and rest.
High Altitude Cerebral Edema (HACE) — Swelling of the brain. A medical emergency. Symptoms: severe headache unresponsive to painkillers, confusion, ataxia (cannot walk in a straight line — the heel-to-toe test), hallucinations, drowsiness progressing to coma. Without descent and treatment, HACE is fatal within 24 hours.
High Altitude Pulmonary Edema (HAPE) — Fluid in the lungs. Also a medical emergency. Symptoms: breathlessness at rest, persistent dry cough (may become productive with pink frothy sputum), extreme fatigue, cyanosis (blue lips/fingertips), gurgling sounds when breathing. HAPE can develop without preceding AMS and is the most common cause of death at altitude.
Prevention: The Golden Rules of Acclimatization
Acclimatization — giving your body time to adapt to lower oxygen levels — is the single most effective prevention strategy. Follow these evidence-based guidelines:
Golden Rules of Acclimatization
1. Above 2,500 m, do not increase your sleeping altitude by more than 300–500 m per day. 2. For every 1,000 m gained, take a rest day (sleep at the same altitude for 2 nights). 3. “Climb high, sleep low” — it is fine to hike higher during the day, but return to a lower camp to sleep. 4. Do not fly or drive directly to altitudes above 3,500 m — if unavoidable, rest for 2–3 days before any physical exertion. 5. Stay hydrated (3–4 liters per day) but avoid alcohol. 6. Never ascend with symptoms of AMS — wait until symptoms resolve before going higher.
Acetazolamide (Diamox) — Prophylaxis and Treatment
Acetazolamide is a carbonic anhydrase inhibitor that speeds up acclimatization by stimulating faster and deeper breathing. It is the most studied and effective medication for altitude sickness prevention.
Prophylactic dose: 125 mg twice daily (morning and evening). Start 24 hours before ascent and continue for 2–3 days after reaching maximum altitude or until descent begins. This dose reduces AMS incidence by 50–75%.
Treatment dose: 250 mg twice daily for established AMS symptoms. Combined with rest and no further ascent.
Side effects: Tingling of fingers, toes, and lips (harmless paresthesia — very common). Increased urination (especially first 24 hours). Altered taste of carbonated drinks (flat taste). Rarely: nausea, drowsiness. Contraindicated in sulfonamide allergy.
Who should take it: Consider prophylaxis if: ascending rapidly (flying to >3,000 m), history of altitude sickness, unable to follow a gradual ascent schedule, or traveling to very high altitudes (>4,500 m). Not routinely needed if following proper acclimatization on a gradual trek.
Dexamethasone and Nifedipine
Dexamethasone is a corticosteroid used for HACE treatment and as a prophylactic alternative for those who cannot take acetazolamide. Dose: 4 mg every 6 hours. It masks symptoms without aiding acclimatization — descent is still mandatory. It is a rescue medication, not a first-line prophylactic.
Nifedipine is used for HAPE prevention and treatment. Dose: 30 mg slow-release twice daily. Consider for travelers with a history of HAPE. It reduces pulmonary artery pressure.
When to Descend Immediately
Emergency: Descend Now
Descend immediately (minimum 500–1,000 m) if: AMS symptoms worsen despite rest and medication. Ataxia develops (unable to walk heel-to-toe in a straight line). Confusion or altered mental status. Breathlessness at rest. Persistent cough with pink/frothy sputum. Cyanosis (blue lips or fingertips). Never leave a person with HACE or HAPE alone. Descend even at night if necessary — waiting until morning can be fatal.
Popular High-Altitude Destinations
Many popular travel destinations are at altitudes where AMS is a risk. Be prepared if visiting: Cusco, Peru (3,400 m) and the Inca Trail. La Paz, Bolivia (3,640 m) and Uyuni. Quito, Ecuador (2,850 m) and volcanoes. Lhasa, Tibet (3,650 m). Kathmandu approach treks, Nepal (Everest Base Camp at 5,364 m, Annapurna Circuit reaching 5,416 m). Kilimanjaro, Tanzania (5,895 m). Ethiopian Highlands (Simien Mountains, 4,550 m). Ladakh, India (Leh at 3,500 m). Colorado ski resorts (2,700–3,800 m).
Special Populations at Altitude
Children: Children under 2 should not sleep above 2,500 m. Older children acclimatize similarly to adults but may not articulate symptoms. Watch for irritability, poor feeding, and disrupted sleep. Acetazolamide dosing: 2.5 mg/kg twice daily (not recommended under 12 by some guidelines).
Cardiovascular disease: Patients with stable heart disease can generally travel to moderate altitude (2,500–3,000 m) with acclimatization. Avoid altitudes above 3,500 m without specialist advice. Altitude increases heart rate, blood pressure, and cardiac workload.
Pregnancy: Limited data. Most guidelines recommend pregnant women avoid sleeping above 3,500 m. Acetazolamide is category C in pregnancy — avoid unless benefits clearly outweigh risks.