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Health Issues at High Altitude
af Dr J.S. Gill
Dr. J.S. Gill er praktiserende narkose læge og smertebehandlings-
specialist på Massachussetts General Hospital
i Boston og "faculty member" i Harvard Medical School.
Han er ivrig bjergbestiger og trekker. I denne artikel, skrevet specielt for Magical Himalaya ApS,
fortæller han om akklimatisering og
generelle sundhedsemner i højderne.
As we climb higher, changes occur in the barometric pressure, temperature, humidity & solar radiation levels. Of these, changes in the atmospheric pressure are probably the most important.
Even though the fraction of oxygen content remains constant, the barometric pressure reduction leads to a fall in the absolute amount. Thus halving the pressure will roughly reduce the available oxygen by 50%.
Acclimatization is a process whereby the body gradually adapts to the lower oxygen with only mild symptoms such as shortness of breath (depending on the altitude). Failure of the body to acclimatize leads to acute mountain sickness (AMS).
There are not many reliable predictors of ease of acclimatization. Previous performance is a good guide to future performance. Older people are less susceptible to high altitude sickness. There does not seem to be a gender difference. Hard physical activity after arriving at high altitude may be deleterious to acclimatization. Benefits of acclimatization are rapidly lost in a few weeks to months at sea level.
Acute mountain sickness (AMS) usually manifests as headache, decreased appetite, lack of energy, disturbed sleep etc and is worst on second day and gradually improves over 3-5 days. It is usually benign. It is commonly seen in younger individuals arriving at high altitude very quickly such as by flight. It is common at altitudes above 3000m but extremely uncommon below 2000m. Mechanism is not clearly known but mild cerebral edema is considered the most likely cause among several other theories.
The most important factors are rate of ascent and the height attained. With slow ascent the incidence may be in the range of 10-30% at 3000-4000m. With fast ascent it may be up to 85%. Younger people are more susceptible and obesity may be a risk factor. It is independent of diet. Smoking may be somewhat protective. Strenuous activity after arriving at high altitude may be a risk factor.
Slow ascent is probably the best way to avoid AMS. As a rough guide ascent should not be more than 300m a day when above 3000m with rest days every 2-3 days if continuously ascending. This may actually be too slow for some. Anyone who experiences significant AMS should go no higher until they feel better. Increased fluid intake may be protective although the evidence for this is largely anecdotal.
Acetazolamide (diamox) has been shown to prevent AMS. Acetazolamide 250 mg three times a day is started 1-2 days before ascent, although it may be equally effective at half that dose. Side effects include increased urination, gastric side effects and tingling in hands & feet. In the end it is up to the individual to decide but slow ascent is probably the best strategy. Dexamethasone at the minimal dose of 4 mg 12 hourly may be equally beneficial.
No treatment is required for AMS. Further ascent should be halted until the individual feels better. For the headache, aspirin & paracetamol are effective. If severe symptoms persist, treatment can be started with acetazolamide 250 mg three times a day. Dexamethasone has also been shown to be effective. Oxygen may or may not help and is often impractical.
High altitude pulmonaty edema (HAPE) is the dangerous form of high altitude sickness. The most important risk factor is rapid ascent, or continuing to ascend with severe AMS and may occur in 1-2% of individuals. It manifests within a few hours with extreme breathlessness, cough with frothy or bloody sputum. Slow ascent and adequate rest are the best prevention. Treatment is descent as soon as possible and even a little descent may dramatically improve the situation. Other supportive measures such as oxygen may not be available at high altitude.
High altitude cerebral edema (HACE) is another dangerous form of AMS. Incidence is difficult to estimate as HACE may merge on a continuum with severe AMS. In addition to symptoms of severe AMS, the individual may experience diminished consciousness, incoherent thought, bad judgment, hallucinations and walking difficulty. Prevention is by slow ascent and not ascending further if experiencing significant AMS. Treatment is rapid descent and dexamethasone if available.
At high altitude there is poor heat production and higher loss. Layering and insulation therefore become very important. Hypothermia sets in very quickly in cold, wet conditions. Keeping the insulation dry, adequate food and hydration are critical. First symptom of hypothermia may be disorientation. Treatment includes maintaining consciousness and preventing further heat loss and active rewarming as soon as possible. Overexposure to ultraviolet rays may occur at high altitude and sunscreens are important.
With prolonged cold exposure freezing injury to hands & feet can occur (frostbite). Preventive measures include keeping warm and hydrated, limiting cold exposure, using appropriate footwear and handwear and keeping an eye on the parts at risk. Once frostbite sets in, treatment involves preventing any injury and rapid thawing only if there is no possibility that the part will freeze again as freeze- thaw- freeze may be very deleterious.
There is evidence that high carbohydrate low fat diet may lead to better endurance at high altitude. In addition fatty foods do not taste very good at high altitude.
Chronic dry cough may develop in some individuals staying at high altitudes for sustained periods of time and this may be related to the cold dry air.
In a study of well-controlled hypertensives at high altitude no significant blood pressure changes were noticed.
In asthmatics an attack of asthma may be precipitated by cold conditions but they do not have a higher risk for AMS.
Significant cardiac conditions such as coronary artery disease may not do well with low oxygen and high work-load, and need to discuss the condition with their doctor before undertaking a high altitude venture. Emergency treatments are unlikely to be available.
Diabetics are likely to experience changing insulin requirements depending on the workload. Although diabetes may not be a contraindication to go to remote mountains and high altitude, detailed discussion with doctor and plans for monitoring sugar levels and treating diabetic emergencies should be made. Insulin freezes at 0 Celcius.
Epilepsy is not worsened at high altitude but if an individual were to have a seizure emergency management may not be available. Individuals who are well controlled with no seizures for a long time may be able to go on treks but still avoid dangerous climbing situations.
Patients with inflammatory bowel disorders should not venture out unless the conditions are quiescent.
In general if an individual suffers from restricting condition it is a good idea to discuss with the doctor before proceeding to the mountains and have detailed plans made. On the other hand, in an asymptomatic healthy individual, detailed testing to identify underlying conditions is probably not indicated.
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