Altitude Sickness on Glaciated Peaks: Prevention and Treatment
Every year, mountaineers, trekkers, and guided glacier visitors underestimate the effects of altitude. The combination of reduced atmospheric oxygen, cold temperatures, physical exertion on technical terrain, and the remoteness common to glaciated environments makes altitude sickness one of the most serious hazards in high mountain travel — and one of the most preventable. Understanding how altitude affects the body, how to recognise the early signs of deterioration, and when and how to act can be the difference between a successful ascent and a medical emergency.
Glaciated peaks concentrate altitude hazards in a specific way. The glaciers that clothe the highest mountains require travel at elevations where the body is under constant physiological stress. Trekkers approaching the Khumbu Glacier on the way to Everest Base Camp cross the 5,000-metre threshold. Climbers attempting routes on Denali in Alaska spend weeks above 4,000 metres. Even relatively accessible glacier experiences such as the Mer de Glace in France or the Athabasca Glacier in Canada, though well below dangerous altitudes, introduce visitors to landscapes where understanding altitude physiology is a useful baseline of knowledge.
How Altitude Affects the Body
At sea level, the atmosphere contains approximately 21 percent oxygen by volume. This proportion remains constant with altitude, but the atmospheric pressure decreases as elevation increases, meaning that each breath contains fewer oxygen molecules. At 3,500 metres, a breath delivers roughly two-thirds the oxygen it would at sea level. At 5,500 metres — the elevation of Everest Base Camp — it delivers about half. At the summit of Everest (8,849 metres), each breath delivers only about one-third the oxygen available at sea level.
The body responds to this reduction in available oxygen through a process called acclimatisation. Breathing rate increases. Heart rate rises. Over days and weeks, the kidneys excrete bicarbonate to shift the blood's acid-base balance, allowing faster and deeper breathing without the alkalosis that would otherwise result. Red blood cell production increases, improving the oxygen-carrying capacity of the blood. The body also increases the density of capillaries in muscle tissue and improves the efficiency with which cells extract oxygen from haemoglobin.
Acclimatisation takes time. Arriving at high altitude quickly — by car, helicopter, or light aircraft — bypasses the time the body needs to adjust and dramatically increases the risk of acute mountain sickness.
Acute Mountain Sickness
Acute mountain sickness (AMS) typically develops within six to twelve hours of arriving at a new higher altitude and affects a significant proportion of people who ascend too quickly. The hallmark symptom is headache, usually frontal or behind the eyes, and often described as similar to a hangover. Nausea, fatigue, dizziness, and disturbed sleep commonly accompany the headache. Loss of appetite is also characteristic.
AMS itself is not immediately life-threatening, but it is a warning. The body is signalling that it is struggling to acclimatise and that further ascent is unwise. The standard response is to stop ascending and rest at the current altitude until symptoms resolve, which usually takes one to three days. Descent of as little as 300 to 500 metres often produces rapid improvement.
Mild AMS can be managed with rest, hydration, and analgesics for the headache. Acetazolamide (Diamox) is a carbonic anhydrase inhibitor that accelerates acclimatisation by increasing breathing rate and is effective both as a preventive medication and as a treatment for AMS when taken at therapeutic doses. It has side effects — notably tingling in the extremities and increased urination — but is well tolerated by most people. It should be discussed with a physician before use, as it is contraindicated for those with sulphur allergies.
High Altitude Cerebral Oedema
High altitude cerebral oedema (HACE) is the severe and potentially fatal end of the AMS spectrum. It occurs when fluid accumulates in the brain as a result of the vascular changes caused by hypoxia. The transition from AMS to HACE can be insidious: progressive worsening of headache, increasing confusion, loss of coordination (ataxia), and eventual loss of consciousness.
The standard field test for HACE is the walk-in-a-straight-line test: if a person cannot place their heel directly in front of their toes and walk ten steps without losing balance, HACE should be suspected and immediate descent initiated. Waiting to see if symptoms resolve spontaneously at altitude with HACE is dangerous. Descent — and rapid descent — is the definitive treatment. Supplemental oxygen, if available, should be administered immediately. Dexamethasone, a powerful corticosteroid, can reduce cerebral oedema and buy time for descent but does not replace descent.
High Altitude Pulmonary Oedema
High altitude pulmonary oedema (HAPE) is the leading cause of death from altitude illness. It involves fluid accumulation in the lungs and develops through a different mechanism from HACE — hypoxia triggers an exaggerated constriction of the pulmonary vasculature, leading to high pressure in the pulmonary capillaries and fluid leakage into the air sacs of the lungs.
Early symptoms include reduced exercise tolerance — a person who was previously keeping pace with the group suddenly falls behind on mild terrain. Dry cough, breathlessness at rest, and a crackling or gurgling sound in the chest on exertion follow. In severe HAPE, the cough becomes productive, with frothy or pink-tinged sputum. Oxygen saturation measured with a pulse oximeter will be unusually low. HAPE can develop at altitudes as low as 2,500 metres in susceptible individuals.
Immediate descent is essential. Unlike HACE, which responds well to dexamethasone, HAPE responds better to nifedipine (a calcium channel blocker that reduces pulmonary vascular resistance) if supplemental oxygen is unavailable. Portable hyperbaric chambers — devices such as the Gamow Bag, which can simulate descent of 1,000 to 1,500 metres — can stabilise a patient while a rescue is organised.
Prevention on Glaciated Peaks
Prevention is enormously more effective than treatment at altitude. The core principle is gradual ascent: gaining no more than 300 to 500 metres of sleeping altitude per day above 3,000 metres, with a rest day every third day. The climbers' maxim "climb high, sleep low" captures the approach of making altitude excursions during the day and returning to lower camps to sleep.
Hydration is important but often overstated: drinking extra water does not prevent altitude illness, but dehydration worsens symptoms and should be avoided. Alcohol and sleeping tablets that suppress respiration should be avoided at altitude. Physical fitness does not protect against altitude illness — highly trained athletes and sedentary individuals are equally susceptible. Individual susceptibility is genetically determined and the only reliable predictor of future altitude illness is a personal history of it.
Before heading to glaciated peaks, consulting the glacier map to research the altitudes involved and the standard itineraries used by guide operators helps you plan realistic acclimatisation schedules. Guided operators on well-established routes such as the Rongai or Marangu routes on Kilimanjaro, or the classic approach to Island Peak in Nepal, build in acclimatisation profiles developed from decades of experience. Following these profiles, respecting symptoms, and maintaining the discipline to descend when the body signals distress is the foundation of safe glacier travel at altitude.