Types of mountain sickness
Acute mountain sickness (AMS) is used here to refer to all the interrelated types of mountain sickness that occur after exposure to altitude, commonly within 2-4 days. In rare cases, AMS may be delayed by as long as three weeks. Chronic mountain sickness is seen mainly in long-term residents at high altitude in the Andes and is not of importance to travelers.
Benign acute mountain sickness is called just ‘AMS’ by some specialists. Sufferers experience loss of appetite, headache, nausea, vomiting, sleeplessness, and a sense of ‘fullness’ in the chest, or some combination of these symptoms. As far as it goes, the condition is fairly harmless, but it may progress to a more serious form. It is therefore not only a nuisance but also an important warning and should not be ignored.
Malignant acute mountain sickness is so called because it may be fatal, and therefore must be handled correctly when it threatens. It may develop from benign AMS or it may begin with little or no warning.
There are two types of malignant AMS, which may occur independently, but the commonest pattern in Nepal is for both to occur together:
Pulmonary acute mountain sickness (high altitude pulmonary edema) Fluid builds up in the lungs. This ‘waterlogging’, together with other changes, leads to breathlessness which persists even at rest, cough, white sputum, and often blueness of the lips (cyanosis).
Cerebral acute mountain sickness (high altitude cerebral edema) Sufferers develop a headache, drowsiness, unsteadiness on the feet, abnormal behavior, impaired consciousness, and often come. If the onset is gradual, the ‘drunken’ walk and inability to sit upright may give clues to what is happening, but commonly the patient passes rapidly into the coma, often overnight so that he or she ‘wakes up unconscious’ the next day.
It would be nice to be able to give a neat, convincing explanation of how AMS is caused. Unfortunately, although there are plenty of theories, there is no general agreement. We do know that patchy high blood flow and increased permeability of the small blood vessels to water are involved in causing edema in the lungs and similar mechanisms may operate in the brain where fragile capillary vessels may be deprived of their usual protection from surges of blood pressure.
Small and even large blood clots are often found in the blood vessels of those who have died from AMS. These may be the result of the nitrogen bubbles discussed earlier, and they may affect the permeability of the capillaries to water. Hormone changes may also play a part, though there is no definite evidence that the menstrual cycle alters women’s susceptibility to AMS or that the use of oral contraceptives is harmful. Another factor may be that low levels of oxygen in the brain interfere with the ability of nerve cells to communicate with each other, a situation that must clearly alter brain function.
For practical purposes, drugs and oxygen have only a minor part to play in the emergency management of AMS, so that a well- informed layman can be as effective as a doctor.
In the event of benign AMS, the rule is to remain at the same altitude until you have recovered. This often takes only one or two days, and you can then ascend cautiously if you wish. If you do not seem to be able to recover in 3-4 days, or if things get worse, you should go down. Some doctors believe that drugs such as dexamethasone or acetazolamide can speed recovery, but this is not recommended routinely.
Malignant AMS sufferers are often in no condition to make decisions for themselves. Their judgment may be impaired as well as their physical capacity. They should be brought down as a matter of urgency. Sometimes they can walk, or stagger down; most sufferers will need to be carried by a porter, yak, or horse. Descent should not be delayed while a helicopter is summoned and it should start even at night if this is possible. An American doctor once saved the life of his wife: he heard her groaning at about midnight and could not awaken her. Recognizing cerebral AMS, he insisted that his Sherpa guide arrange for her to be carried down at once. She eventually recovered, but it was touch and go; if he had delayed until morning, she would certainly have died.
When evacuating a cerebral AMS victim, it is important to prevent obstruction to breathing. Patients lying on a stretcher should be turned to one side. Pulmonary AMS patients are often more comfortable in the sitting position and may be brought down sitting on a yak or in a basket on a porter’s back; the head should always be kept forward. If oxygen is available, give it, but this is much less important than decent. No drugs are known to be helpful for malignant AMS.
Patients with pulmonary AMS often improve rapidly after a descent of 2000-3000 feet. However, patients with cerebral or mixed AMS may not regain consciousness for days or even weeks, though recovery, when it occurs, is usually complete.
I have said enough to make it clear that gradual ascent is the key to prevention. The schedule for any given journey has to depend on local details, but it is essential to avoid rapid ascents and to allow time to acclimatize above 8000 feet.
Those who fly to high-altitude airfields must be prepared to spend time acclimatizing on arrival. In addition, I recommend ‘rest days’ every 3000 feet above 9000 feet. On the Everest trek, for example, it is advisable to stay two nights in the region of Namche Bazaar (11 300 feet, 3450 m) and another two at Per- the (14 000 feet, 4250 m). During these ‘rest days’, you can actually climb as high as you like, provided you return to sleep at the same altitude as the previous night. ‘Climb high, sleep low’ is a useful motto. The Himalayan Rescue Association in Kathmandu provides advice on safe schedules for Nepal.
Drugs such as acetazolamide (Diamox), spironolactone, and dexamethasone have been recommended for the prevention of AMS. They can prevent the symptoms of benign AMS but severe and even fatal AMS has occurred in people taking these drugs. They may have an adverse effect by hiding the warning symptoms. Though they may be necessary for rescue parties, I do not recommend them for travelers. It is much safer to rely on good planning and gradual ascent.
It is always good to be physically fit for a walk or climb, but unfortunately, this does not prevent AMS. In fact, some of the fittest have become victims for the obvious reason; they go up too fast.
It is not yet possible to identify the type of person who is most at risk, but those who have previously suffered from AMS should ascend particularly cautiously. One experienced Alpine guide, unused to Himalayan altitudes, was evacuated with malignant AMS in two successive seasons. Many others have had multiple attacks, but some seem never to be affected.
Other problems at altitude
Some people develop swelling of the body at high altitude (high altitude subcutaneous edema). Many of these are otherwise well, although some may show the features of benign AMS. The swelling should probably be regarded as a warning sign.
Bleeding at the back of the eye (high altitude retinal haemorrhage) occurs in many people but most are not aware of it unless a doctor examines their eyes with an ophthalmoscope. Only rarely may vision be affected, and then usually only temporarily.
If you have significant disease of the heart, lungs, or blood, you will probably find it difficult to tolerate the extra strain placed on the body by high altitude, especially if you are planning to walk or climb. It is extremely important that you consult your doctor for advice about going to high altitude.
Epilepsy and migraine are conditions that occur in attacks, and there may be more risk of an attack at high altitude. Many asthmatics, on the other hand, do not have attacks at altitude, unless precipitated by exertion or cold.
People with sickle cell disease or trait (which only affects black people) usually know that they have the condition but may not be aware that they may get ‘crises’ at high altitude. These are painful and may be dangerous.