Acute Mountain Sickness (AMS) is the mildest and most common form, typically occurring above 2,500m. Symptoms include headache, fatigue, nausea, dizziness, and difficulty sleeping. AMS is usually manageable with rest, hydration, and avoiding further ascent until symptoms resolve — most cases improve within 24-48 hours without descent.
High Altitude Pulmonary Edema (HAPE) is a buildup of fluid in the lungs, typically occurring above 4,000m. Warning signs include severe shortness of breath even at rest, a persistent cough (sometimes producing pink or frothy sputum in severe cases), extreme fatigue, and a feeling of suffocation, especially when lying down. HAPE can progress rapidly — sometimes within hours — and is a medical emergency requiring immediate descent. Oxygen and medication (such as nifedipine) can help stabilise a patient, but descent — by foot, yak, or helicopter — remains the definitive treatment.
High Altitude Cerebral Edema (HACE) is swelling of the brain due to altitude, also typically above 4,000m, and is the most dangerous of the three. Warning signs include severe headache unresponsive to medication, confusion, loss of coordination (ataxia — difficulty walking a straight line is a classic early sign), hallucinations, and in severe cases, loss of consciousness. HACE can be fatal within hours if untreated. Like HAPE, immediate descent is critical, and helicopter evacuation is often the only realistic option for rapid descent from remote high-altitude locations.
Why helicopter evacuation matters: in regions like the Everest Base Camp trail above Namche Bazaar, or the Annapurna Circuit above Manang, descending several thousand metres on foot can take a full day or more — time a HAPE or HACE patient may not have. A helicopter can reduce that descent to under an hour, often making the difference in outcome.
