Altitude illness: the rules that have not changed

Altitude illness is one of the few mountain hazards with a well-established management protocol that has stayed broadly stable for decades. The rules are simple. The difficulty is that following them requires giving up time and summits, and people do not want to.

This is general information; it does not replace training in mountain medicine or advice from a doctor who knows your history.

What causes it

At altitude the air pressure falls, so each breath delivers less oxygen. The body compensates over days — breathing rate, red cell production, and a range of other adaptations — and that process is acclimatisation. Illness occurs when you ascend faster than the adaptation can keep up.

Susceptibility varies enormously between individuals and does not track fitness. Very fit people get altitude sick; unfit people sometimes do not. A previous good experience at a given altitude is somewhat reassuring but not a guarantee.

Acute mountain sickness

Typically appears some hours after arriving at a new altitude, commonly above roughly two and a half thousand metres.

Headache is the cardinal symptom, usually accompanied by some of: nausea or loss of appetite, fatigue out of proportion to the effort, dizziness, and poor sleep.

The practical rule of thumb widely taught: a headache at altitude is altitude illness until proven otherwise.

Management: stop ascending. Rest at the current altitude, hydrate, take simple painkillers for the headache. Most people improve within a day or two and can then continue. If symptoms worsen, or do not improve with rest, descend.

The single most important rule: never ascend with symptoms.

High altitude cerebral oedema

Swelling of the brain. Life-threatening, and it can progress from mild symptoms to unconsciousness within hours.

The signs to watch for: ataxia — loss of coordination, most reliably tested by asking someone to walk heel to toe in a straight line — plus confusion, altered behaviour, severe headache unrelieved by painkillers, and drowsiness.

The heel-to-toe walk is the field test. Anyone at altitude who cannot do it should be treated as having cerebral oedema until proven otherwise.

Management: descend immediately, at any hour, in any weather that permits it. Do not wait for morning. Supplementary oxygen and a portable hyperbaric chamber if available, and medication as per training — but descent is the treatment and everything else buys time for descent.

High altitude pulmonary oedema

Fluid in the lungs. Also life-threatening, and it can occur without any preceding mountain sickness symptoms.

Signs: breathlessness at rest — the key distinguishing feature — a dry cough progressing to a wet one, sometimes with pink frothy sputum, extreme fatigue, a rapid heart rate, and a marked drop in exercise capacity. Someone who could climb yesterday and cannot walk fifty metres today is a serious concern.

Management: descend immediately. Oxygen, keep them warm, minimise exertion — descent by helicopter or with assistance is preferable because exertion worsens it.

Prevention: the ascent profile

The widely used guidance above roughly three thousand metres is to increase your sleeping altitude by no more than three to five hundred metres per day, and to take a rest day every three or four days or every thousand metres or so of gain.

The principle behind it: climb high, sleep low. Going high during the day and returning to sleep lower is good acclimatisation and is what most successful expedition profiles do.

Flying or driving directly to a high altitude removes the gradual gain entirely and is a common cause of severe illness in trekkers arriving at high airfields.

Other prevention

Hydrate adequately, though not excessively. Avoid alcohol and sedatives, particularly in the first days, because they depress breathing. Eat plenty of carbohydrate. Do not exhaust yourself in the first days at a new altitude.

Medication for prophylaxis exists and is used widely, particularly where a fast ascent profile is unavoidable. It is a genuine aid to acclimatisation and it is not a substitute for a sensible profile. Discuss it with a doctor before the trip, including side effects and interactions.

Group management

Say at the start that anyone with symptoms says so immediately, and that descending with someone is a normal, expected part of the trip rather than a failure.

The pattern in altitude deaths is depressingly consistent: someone had symptoms, did not want to hold up the group or lose the summit, kept going, and deteriorated. Group culture prevents that, and nothing else does.

Never leave a symptomatic person alone. Cerebral oedema impairs judgement, which means the affected person becomes progressively less able to make the decision to descend.

And be sceptical of the idea that pushing through works. At altitude, the reliable treatment is going down, and it works quickly. There is no equivalent that works by continuing up.