Altitude sickness, also known as acute mountain sickness (AMS), is a pathological effect of high altitude on humans, caused by acute exposure to low partial pressure of oxygen at high altitude. It commonly occurs above 2,400 metres. It presents as a collection of nonspecific symptoms, acquired at high altitude or in low air pressure, resembling a case of “flu, carbon monoxide poisoning, or a hangover”. It is hard to determine who will be affected by altitude sickness, as there are no specific factors that correlate with a susceptibility to altitude sickness. However, most people can ascend to 2,400 metres (8,000 ft) without difficulty.
Acute mountain sickness can progress to high altitude pulmonary edema (HAPE) or high altitude cerebral edema (HACE), which are potentially fatal.
Chronic mountain sickness, also known as Monge’s disease, is a different condition that only occurs after very prolonged exposure to high altitude.
What causes altitude sickness?
Air is “thinner” at high altitudes. When you go too high too fast, your body cannot get as much oxygen as it needs. So you need to breathe faster. This causes the headache and other symptoms of altitude sickness. As your body gets used to the altitude, the symptoms go away.
What are the symptoms?
The symptoms of altitude sickness include:
- A headache, which is usually throbbing. It gets worse during the night and when you wake up.
- Not feeling like eating.
- Feeling sick to your stomach. You may vomit.
- Feeling weak and tired. In severe cases, you do not have the energy to eat, dress yourself, or do anything.
- Waking up during the night and not sleeping well.
- Feeling dizzy.
- Your symptoms may be mild to severe. They may not start until a day after you have been at a high altitude. Many people say altitude sickness feels like having a hangover.
Altitude sickness can affect your lungs and brain. When this happens, symptoms include being confused, not being able to walk straight (ataxia), feeling faint, and having blue or gray lips or fingernails. When you breathe, you may hear a sound like a paper bag being crumpled. These symptoms mean the condition is severe. It may be deadly.
If you are going on a high-altitude trek, learn about altitude sickness, its symptoms, and how to treat it. Look out for other people in your group.
High-Altitude Pulmonary Oedema (HAPE) Causes
‘Pulmonary’ refers to the lungs and ‘oedema’ means that there is a build-up of fluid. So, pulmonary oedema is a build-up of fluid within the lungs. The exact reasons why high-altitude pulmonary oedema (HAPE) can develop are unknown. It is thought that the high altitude causes an increase in pressure in the blood vessels around the lungs which leads to smaller blood vessels becoming ‘leaky’, allowing fluid to escape from the blood vessels into the lungs.
High-Altitude Pulmonary Oedema Symptoms
If someone develops HAPE, the symptoms usually start to appear a few days after arrival at altitude. They start with shortness of breath on exertion and then worsen so that there is shortness of breath even when resting. Someone can also develop a cough and feel generally weak and tired. They may start to cough up pink/frothy liquid (sputum) and complain of chest tightness. They may have swelling of their ankles or legs and their lips or fingernails may be blue or grey. In severe cases they become extremely short of breath at rest and drowsy. Coma and death can occur if HAPE is not treated quickly.
HAPE can happen in someone who also has acute mountain sickness (AMS) or high-altitude cerebral oedema (HACE), or they may have no obvious symptoms of these other problems.
What is the treatment for High-Altitude Pulmonary Oedema?
Again, someone with HAPE needs to move down (make a descent) to a lower altitude immediately. Even a descent of a few hundred metres can make a difference but ideally descent should be at least to the last altitude at which the person woke up feeling well. Treatment with oxygen and the medicine nifedipine may also help symptoms but does not replace the need for descent.
A hyperbaric chamber (as explained above) can be used if descent is not possible and/or oxygen and other treatment are not available.
High-Altitude Pulmonary Oedema Prognosis
HAPE tends gets better quickly on descent and there is usually complete recovery.
High-Altitude Cerebral Oedem (HACE)
High-altitude cerebral oedema (HACE) usually develops in someone who already has acute mountain sickness (AMS). The swelling of the brain that has led to AMS gets worse and starts to interfere with the function of the brain. So, HACE is really a severe form of AMS.
Symptoms of High-Altitude Cerebral Oedema
Symptoms of HACE include headache, nausea, vomiting, hallucinations (for example, seeing or hearing things that are not actually there), feeling disorientated and confusion. Often these symptoms are not noticed by the person who is developing HACE, or by their companions. An affected person can lose their co-ordination and become unsteady on their feet. As the cerebral oedema progresses, their consciousness level will drop and coma and death can occur if treatment is not started. Fits (seizures) can also occur.
HACE can develop quickly, over a few hours. Someone may also have symptoms of high-altitude pulmonary oedema (HAPE) – see below.
Treatment for High-Altitude Cerebral Oedema
This is a move down (a descent) to a lower altitude immediately. If this does not happen, or is delayed, death can occur. Treatment with oxygen and the medicine dexamethasone (a steroid medicine) can help to relieve symptoms and can mean that getting someone down to a lower altitude becomes easier. However, these treatments do not remove the need for descent. The descent should be at least to the last altitude at which the person woke up feeling well.
A device has been developed called a portable hyperbaric chamber. It is, essentially, an airtight bag that is pressurised by a pump. The person with HACE is placed inside it and it can provide the same effect as (simulate) descent. They will be breathing air equivalent to that at much lower altitude. This can be life-saving when descent is not possible and oxygen is unavailable.
High-Altitude Cerebral Oedema Prognosis
People with HACE usually do well if they descend to a lower altitude soon enough and far enough. They will usually have a complete recovery.
Altitude Sickness Prevention
Go up slowly, take it easy, and give your body time to get used to the altitude. The body has an amazing ability to acclimatise to altitude, but it needs time. For instance, it takes about a week to adapt to an altitude of 5000m.
- If you are going to altitudes higher than 8000 ft (2438 m), try to spend a night at a medium altitude before going higher. For example, in the United States, spend a night in Denver before going to the Rocky Mountains.
- Do not fly into high-altitude cities. If this is not possible, avoid large meals, alcohol, and being very active after you arrive. Rest, and drink plenty of liquids. If you have symptoms, do not go higher until they have gone away. Examples of high-altitude cities include Cuzco, Peru; La Paz, Bolivia; and Lhasa, Tibet.
- Sleep at an altitude that is lower than the altitude you were at during the day. For example, if you ski at 9500 ft (2896 m) during the day, sleep the night before and the night after at 8000 ft (2438 m). “Climb high, sleep low” is standard practice for those who spend time at high altitudes.
- One study showed that starting to take ibuprofen 6 hours before climbing to high elevations and then taking it every 6 hours while climbing may help prevent altitude sickness.1 Ibuprofen may also reduce the symptoms of altitude sickness if you do get it.
- You may consider taking acetazolamide (Diamox) or possibly dexamethasone before going to a high altitude.2 Talk to your doctor about this.
- Eat a lot of carbohydrates. This includes breads, cereals, grains, and pasta.