chapter 20. On the mountain
JM Queally and D McCormack
INTRODUCTION
More and more people are visiting high altitude areas (Fig. 20.1) while skiing, trekking, mountaineering or even visiting a city at altitude (e.g. La Paz in Bolivia at 4200 m). Altitude sickness can range from simple fatigue to life-threatening coma. It is related to individual physiology (genetics) and the rate of ascent, and not to age, gender, physical fitness or previous altitude experience.
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| Fig. 20.1 |
This chapter shows how to recognize and treat the various forms of altitude illness. Acute mountain sickness is the most common form of altitude illness experienced. Treatment often involves simple actions such as rest or descent. However at more extreme altitudes where severe forms of altitude illness are more likely to occur, treatment is often difficult as medical resources are usually limited.
What is high altitude?
• Practically speaking, altitude illness rarely occurs below 2500 m
Acclimatization
Acclimatization is the normal physiological process of the body adjusting to the decreased availability of oxygen at high altitudes. The body recognizes that oxygen is in short supply and takes a number of steps to increase the amount of oxygen taken in, and more importantly to use that oxygen more efficiently than normal. As you ascend, each breath contains less and less oxygen. To compensate for this lack of oxygen, breaths taken are deeper and more frequent, particularly on exertion (e.g. trekking). This is normal and an important mechanism in adapting to the lack of oxygen. Occasionally ‘periodic breathing’ can occur, particularly at night. This consists of cycles of normal breathing that gradually slow to a period of not breathing for up to 15 seconds. This is then followed by a brief recovery phase of rapid breathing. Even though this may cause anxiety, it is important to realize that this is not altitude sickness but rather a manifestation of the normal acclimatization process. Rates of acclimatization differ between individuals. After 10 days at altitude the body is approximately 80% acclimatized for most people.
Normal symptoms at altitude
• Hyperventilation (faster and deeper breathing) on exertion
• Periodic breathing
• Insomnia
• Increased urination
• Increased heart rate (up to 100 beats per minute)
Prevention is key!
Plan a gradual ascent that allows your body sufficient time to acclimatize. Be aware of the signs and symptoms of acute mountain sickness so you can identify and treat any problems early. It is important to remember that acclimatization occurs at different rates for different individuals. As a rule the following guidelines will prevent altitude illness in most individuals.
• Before going above 3000 m, spend at least one night at an intermediate elevation below 3000 m. It is not advisable to ascend from sea level up to above 3000 m without spending a night acclimatizing at approximately 2000 m. People do quite commonly fly into ski resorts from sea level and start skiing at 3000 m the following day. They should be made aware of the higher risk of developing acute mountain sickness
• Above 3000 m your sleeping elevation should not increase more than 300-500 m per night
• For every 1000 m gain in elevation you should spend a second night at the same elevation. When spending a second night at the same elevation it is useful to ascend to a higher elevation on a short trek during the intervening rest day, returning to the lower elevation to sleep. This helps acclimatization and allows recovery at night, ensuring you are ready for a longer ascent in the morning
Climb high, sleep low
• Avoid dehydration. Dehydration occurs more easily at altitude because of the increased breathing rate, which means that more moisture is lost from the lungs than normal
• Nutrition is important. On activity days a high carbohydrate diet is advised as carbohydrates require less oxygen to metabolize (burn) than fats and proteins, which should be eaten on rest days. Your energy requirements also increase to approximately 4000 kilocalories per day
• Avoid respiratory depressants (substances that reduce your drive to breathe):
• Alcohol
• Opioid painkillers
• Sleeping tablets (at altitude do not treat insomnia with sleeping tablets – they will only exacerbate acute mountain sickness as they reduce your ability to breathe properly)
ALTITUDE ILLNESS
What should I check for?
Speak to the person
• When assessing a patient the safety of both the rescuer and the patient is important. For example, if on a glacier, ensure everyone is attached to a safety rope, then speak to the person
• Ensure the patient is conscious and can speak in complete sentences (see the ABC chapter (p. 21))
Problem identification – ask questions
• To assess if the person is orientated or confused
• ‘Where are you?’
• ‘What day and date is it?’
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