Altitude sickness and acclimatisation are important elements in serious mountaineering. Roy McGregor explains what to expect and how to prepare
Acclimatisation is the deliberate, temporary modification of your physiology to cope with increased altitude. There are practical limits to altitude acclimatisation, and it is simply not possible to become permanently acclimatised to much above 5,000m, as the body inevitably deteriorates. Short term acclimatisation to about 6,500m is the best that a fit climber can hope for.
The demand on your muscles depends on your activity level, but your brain needs a surprising amount of oxygen. Despite being only 2% of your body weight, it needs around 15% of your oxygen intake. If your brain is deprived of oxygen, your judgement declines, movement control suffers and speech becomes confused.
Your body responds in various ways to needing more oxygen.
In simple terms:
You start to breathe faster right away and your heart rate rises within minutes. It can take several days before your blood levels change: if you suddenly find yourself urinating a lot that may be a sign that your body is acclimatising well. Making more red blood cells is a much longer process that gets underway within a week or two: on trips such as Kilimanjaro, this won't be in time to make a difference.
|Mild AMS||Symptoms include headache, fatigue, stomach illness, dizziness, nausea, pins and needles, swelling of hands and feel, sleep disturbance|
|Moderate AMS||Severe headaches that are not relieved by medication, nausea and vomiting, increasing weakness and fatigue, shortness of breathe, decreased coordination (ataxia)|
|Shortness of breath at rest, inability to walk, decreasing mental status, build-up of fluid in the lungs|
There are two life threatening conditions associated with severe altitude sickness: High Altitude Cerebral Oedema (HACE) – swelling of the brain and High Altitude Pulmonary Oedema (HAPE) – fluid in the lungs.
Prevention is better than treatment. The best form of treatment is to descend.
You can minimise the effects and risks of altitude by pre-acclimatising before you go. During the course of your consultation you will be tested at 3,000m and 5,000m to see how you will cope. If you are fine, then you go on your trip with peace of mind and confidence. If you are susceptible then you have to option of doing further training before you go, this may include passive or active simulated altitude sessions or hiring equipment to use in your own home.
The most important thing after all the time and money you have put into a trip is to have a happy and enjoyable time. Getting tested for AMS can help you with this.
Your body is under increased stress. Even minor problems at altitude can rapidly become serious, so please take greater precautions to maintain good health.
For every 1,000m climbed the air temperature drops by approximately 6.5 degrees Celsius. Bad weather, especially wind, can obviously make things worse. Wear suitable clothing to deal with the changeable weather conditions.
The cold also has a significant effect on your metabolism. Additional energy is required to keep your body warm. Generating warmth can only come from 'burning' food and this requires oxygen, which is of course in short supply. Keep eating even though you don’t feel hungry.
The dangers of frostbite and hypothermia are serious, but are not covered here. Please remember if you take your glove off to take a photo or drink on a windy mountain, they are likely to be blown away.
Top Tip: take some chemical hand warmers with you, great for the hands but also good for warming your sleeping bag.
The sun's rays are far stronger at altitude because the thinner air screens out less of the harmful radiation. Since the equatorial sun if already much stronger than most tourists are used to, the risk of sunburn is doubly severe.
Bring a sun hat, clothing to cover up ad suncream with the highest Sun Protection Factor you can find. A minimum of SPF 25 is recommended for you face and SPF 33 for your lips which are especially at risk.
Top Tip: Take high quality sunglasses that block out the sun from the side and make things nice and dark.
Adequate hydration is essential to allow the body to regulate its chemical balance in response to the change in altitude. Aim to drink 3-4 litres (nearly 7-9 pints) per day. If possible try to add electrolytes to your water, two brand names to consider are Nuun and Dioralyte, these will help to replace the body's salts that are lost while walking.
A serious effect of dehydration is the blood becomes thicker with additional risk of strain on the heart and circulatory system and general impairment of performance. Aspirin can be taken to help thin the blood.
The air at high altitude is always very dry. With each breath water will be stripped from your lungs. If you use your mouth to breathe a dry cough is likely to develop.
Top Tip: Try to use your nose to breathe through to prevent a dry throat. If this is not possible, suck a honey cough sweet to help lubricate the throat.
People who have problems sleeping at sea level may find their sleeping patterns disrupted even more at altitude. Those who sleep well at home are often able to sleep well at altitude.
Above 3,000 metres (10,000 feet) people may experience periodic breathing known as Cheyne-Stokes Respirations. Shallow breathing occurs during sleep and the person often becomes restless and may awake with a sudden feeling of shortness of breath. A good night's sleep is important for the body to repair and recover itself, but taking a sleeping pill is extremely dangerous and should be avoided as the body is already lethargic and could easily slip into a coma.
Top Tip: Take some ear plugs, especially if you are sharing a cabin with others.
It's very difficult to maintain appetite at high altitude. The sense of smell and taste are greatly inhibited and the general feeling of lethargy and nausea that can accompany mild altitude sickness compound to put one off eating.
Fatty foods and high-tech sports nutrition bars are difficult to digest and should be avoided. There are some advantages in taking vitamin and mineral supplements at altitude.
A symptom of AMS is constipation and diarrhoea which tend to alternate and this can be dangerous as well as distressing. Some medications may help to regulate the system. On most organised treks the water is boiled and cooled to sterilise the water. Those with sensitive stomachs may consider iodine tablets to further treat the water.
Top Tip: To neutralise the taste of iodine dissolve an effervescent Vitamin C (ascorbic acid) tablet into the water.
Menstruation may be upset during the acclimatisation process, and while this seems unlikely to cause harm, it could be inconvenient. Female climbers may wish to prepare for this or make medicinal arrangements beforehand. Oral contraceptives may be less effective at high altitude and there may also be an increased risk of thrombosis, as with any oestrogen-based medicine. These matters should be discussed with your doctor.
Control what you can control
At altitude we encounter more physical stress. Give your body the best possible chance by controlling the stresses that are within our physical control: Hydration, nutrition, body temperature, mental calmness and getting a good night's sleep. By looking after these your body can concentrate on surviving with the stress of reduced oxygen.