Acute Mountain Sickness (AMS) Acute Mountain Sickness is caused by the relative lack of oxygen at high altitudes. In its mildest form, altitude sickness can occur at heights as low as 2000 metres; however, most people won’t get symptoms until above 2700m or higher, depending on the speed of ascent.
Symptoms Mild cases of altitude sickness usually involve headaches, nausea, breathlessness, palpitations (rapid heartbeats) and reduced ability to exercise. This is called acute mountain sickness. More serious forms of altitude sickness occur at higher altitude (usually defined as more than 3000 metres). In addition to the symptoms already mentioned, affected people may lose their appetite and have difficulty sleeping, and they may wake up frequently through the night due to ‘periodic’ breathing. Periodic breathing is when a person breathes normally then stops breathing for 10 to 15 seconds, which wakes them up. Severe breathing difficulties, vomiting, frequent cough, lack of coordination, confusion, severe headaches and even loss of consciousness are among the more serious symptoms. These serious forms of AMS are called high altitude pulmonary oedema (HAPE) when the lungs are affected and high altitude cerebral oedema (HACE) when the brain is affected. Although both these conditions are uncommon, they are potentially fatal.
Risk Factors There is no way of predicting who will, or will not, suffer from altitude sickness. Surprisingly, increased age, lack of fitness and illnesses such as asthma do not seem to make people more prone to the problem. Having had altitude sickness before does not mean that you will necessarily get it again; however, you will be more susceptible. Similarly, having been okay at high altitude previously does not guarantee that you will be okay next time. Most people with chronic illnesses can safely travel to high altitudes, but some diseases make high altitude travel dangerous.
Prevention The best way to avoid altitude sickness is to ascend slowly, taking several days to reach the intended destination. This allows the body time to get used to the decreasing supply of oxygen available at high altitude and is a process is called acclimatisation. At high altitudes it can take three to five days for your body to acclimatise before you should ascend further. If it is not possible to acclimatise — for example, if you are taking a short flight from sea-level to 3000 metres or more — acclimatisation can be helped by taking the medicine Diamox (acetazolamide), which is started one day before the planned trip and continued for 2 to 3 days at altitude. Diamox works by increasing a person’s breathing rate and helps with acclimatisation. It is important to stay hydrated when at high altitude. Dehydration is a contributing factor to altitude sickness. Much water is lost in the breath in cold, high altitudes, and also by evaporation through sweat, especially when undergoing activities such as skiing or trekking. Avoiding strenuous activity in the first 24 hours at high altitude reduces the symptoms of AMS.
Alcohol and sleeping pills are respiratory depressants, thus slow down the acclimatization process and should be avoided. Alcohol also tends to cause dehydration and worsens AMS. Altitude acclimatization is the process of adjusting to decreasing oxygen levels at higher elevations, in order to avoid altitude sickness. Once above approximately 3,000 metres (10,000 feet), most climbers and high-altitude trekkers take the ‘climb-high, sleep-low’ approach. For high-altitude climbers, a typical acclimatization regimen might be to stay a few days at a base camp, climb up to a higher camp (slowly), and then return to base camp. A subsequent climb to the higher camp then includes an overnight stay. This process is then repeated a few times, each time extending the time spent at higher altitudes. The general rule of thumb is to not ascend more than 300 metres (1,000 ft) per day to sleep.
Treatment The symptoms of acute mountain sickness will usually disappear in a few days without treatment if the person stays at the same altitude. Drinking plenty of fluids and taking pain killers (analgesics) for the headache may also help. A medicine called acetazolamide (brand name Diamox) may also be given to people who have mild to moderate symptoms, or a corticosteroid called dexamethasone may be given if symptoms are more severe. People with serious altitude sickness need immediate descent, in addition they may be given oxygen, or to be put in a portable altitude chamber or bag (such as a Gamow bag).
DIAMOX What is Diamox? Diamox (Acetazolamide) is a sulphur-based tablet, which aids in acclimatisation to high altitude. It must NOT be taken by anyone with an allergy to sulphur drugs. It is also used in higher doses to rid the body of excess fluid (ie a diuretic). There may be other reasons Diamox is not suitable for you, so it should only be taken after being prescribed by a doctor.
How does it work? Diamox works by changing the ‘acid-based’ balance in your blood. As a result of this, your brain tells you to breathe more, and this increased ventilation (breathing) helps your body to acclimatise more rapidly to the decreased oxygen in the air available at altitude.
Are there any side effects? The most common side effect is tingling in the hands and feet, especially for a few hours after taking the tablets. Occasionally people experience a mildly upset stomach, and, rarely, increased sensitivity to the sun. Because diamox is a diuretic it is important to maintain an adequate fluid intake. Failure to do this can cause bladder infections or constipation.
What is the dose? 125mg or half a tablet twice a day.
When should I take Diamox? Diamox can be used in two ways: 1 To help prevent AMS 2 To treat mild AMS. [It works better as a preventative than a treatment]. As a preventative measure Diamox is best used on trips where you are rapidly ascending to high altitudes. On this type of trip you may not have enough time to acclimatise naturally and if you suffer from altitude sickness your enjoyment of the trip will be diminished. Examples are: Climbing Mt Kilimanjaro or spending just a few days in the Andes of Peru or Bolivia. In these cases you should start taking Diamox the day before you ascend to altitude and continue for 2 more days at your maximum altitude. You can stop it on descent. Another option is to see how you feel, and commence Diamox only if you are unable to acclimatise easily. The best treks are those that allow you to acclimatise slowly, for example, most treks in Nepal. It is advisable to follow the suggested acclimatisation guidelines but to have some Diamox as backup if required. Remember, Diamox should NEVER be regarded as a substitute for IMMEDIATE descent if you or one of your group is suffering severe illness or worsening symptoms of AMS. It does not mask the symptoms of AMS, although onset may be at a higher altitude than if not taking it. It can, however, be useful to start taking Diamox if you have persistent mild symptoms after 24 – 48 hours at a particular altitude. Only if your symptoms disappear after taking Diamox can you safely continue your trek. You can then stay on the Diamox until you have returned to an altitude below that at which you got symptoms. If your symptoms don’t settle you should descend to a lower altitude.
It is important not to rely on Diamox as a substitute for descent if you are developing worsening symptoms of Acute Mountain Sickness
NB: This is general advice only and does not take into account any individual persons medical circumstance. Prior to travelling to altitude you should make an appointment to see one of our experienced travel doctors.