Preventing Acute Mountain Sickness

Like any medical condition, the prevention of mountain sicknes is always better than the cure.

Acute mountain sickness is caused by a lack of oxygen in the body of individuals exposed to higher elevations. This usually occurs when they travel to an altitude over 10,000 feet (3,000 metres) without proper acclimatisation before engaging in physical activities. Mountain climbers, trekkers, skiers, and travellers to the Andes or Himalayas etc. are at greatest risk.

While individual tolerance varies, symptoms usually appear within several hours of ascending, with those in poor physical condition being most susceptible. Headache, fatigue, shortness of breath, nausea, and poor appetite occur initially. Inability to sleep is also frequently reported. In more severe cases thinking and judgement may become impaired.

An uncommon but potentially fatal complication called high altitude pulmonary or cerebreal oedema (HAPO & HACO), caused by fluid build-up in the lungs and brain, can also occur.

The symptoms of acute mountain sickness can be prevented or minimized by gradually ascending (less than 500 meters/day) over several days to give your body a chance to acclimatize to the higher altitude.

Once the symptoms begin to occur, they usually subside over several days without treatment provided there has been adequate time for acclimatisation. However, if they worsen, they can be relieved with the administration of oxygen or descent to a lower altitude.

Drugs Used:

Acetazolamide (Diamox): This is the most tried and tested drug for altitude sickness prevention and treatment. Unlike dexamethasone (below) this drug does not mask the symptoms but actually treats the problem. It works by increasing the amount of alkali (bicarbonate) excreted in the urine, making the blood more acidic. Acidifying the blood drives the ventilation process, which is the cornerstone of acclimatization.

For prevention, one 250mg tablet should be taken daily starting one or two days before and continuing for three days once the highest altitude is reached. Blood concentrations of acetazolamide peak between one to four hours after administration of the tablets. It may therefore, be better to take 125mg (half a tablet) twice daily. Gradual ascent is always desirable to try to avoid acute mountain sickness even when acetazolamide is being taken.

Studies have shown that prophylactic administration of acetazolamide at a dose of 250mg every eight to twelve hours before and during rapid ascent to altitude results in fewer and/or less severe symptoms (such as headache, nausea, shortness of breath, dizziness, drowsiness, and fatigue) of acute mountain sickness (AMS). Pulmonary function is greater both in subjects with mild AMS and asymptomatic subjects. The treated climbers also had less difficulty in sleeping.

However, gradual ascent is always desirable to try to avoid acute mountain sickness but if rapid ascent is undertaken and actazolamide is used, it should be noted that such use does not obviate the need for a prompt descent if severe forms of high altitude sickness occur, i.e. pulmonary or cerebral oedema.

Side effects of acetazolamide include: an uncomfortable tingling of the fingers, toes and face carbonated drinks tasting flat; excessive urination; and very rarely, blurring of vision.

On most treks, gradual ascent is possible and prophylaxis tends to be discouraged. Certainly if trekkers do develop headache and nausea or the other symptoms of AMS, then treatment with acetazolamide is fine. The treatment dosage is 250 mg twice a day for about three days.

Acetazolamide may be obtained on prescription in the UK from Doctor Fox

Dexamethasone: This powerful steroid type drug can be life saving in people with HAPO & HACO, and works by decreasing brain swelling and reducing the pressure in the skull. The dosage is 4 mg three times per day, and obvious improvement usually occurs within about six hours. It's use is highly specialised and can be very dangerous if used incorrectly or by inexperienced persons.

It can be a good "emergency drug" since it "buys time" especially at night when it may be problematic to descend. Descent should be carried out as soon as possible the next day. It is unwise to ascend while taking dexamethasone: unlike diamox this drug only masks the symptoms.

Dexamethasone can be highly effective: many people who are lethargic or even in coma will improve significantly after tablets or an injection, and may even be able to descend with assistance. Many pilgrims at the annual festival at Gosainkunda lake in Nepal suffer from HACO following a rapid rate of ascent, and respond remarkably well to dexamethasone. Mountain climbers also sometimes carry this drug to prevent or treat AMS. However, it needs to be used cautiously. It has been known to cause stomach irritation, euphoria or depression.

It may be a good idea to pack this drug for a high altitude trek for emergency usage in the event of HACO. In people allergic to and therefore unable to take acteazolamide, dexamethasone can also be used for prevention: 4 mg twice a day for about three days should be sufficient but only under experienced supervision.

Nifedipine: This drug is normally used to treat high blood pressure and angina, but also seems able to decrease the narrowing in the pulmonary artery (pulmonary vasodilation) resolving the pulmonary hypertension responsible for the high pressure leak in the lungs caused by low oxygen levels, thereby improving oxygen transfer. It can therefore be used in the treatment of HAPO, though unfortunately its effectiveness is not anywhere as dramatic that of dexamethasone in HACE. Oxygen saturations gusually improve slightly after administration of nifedipine. The dosage is 20 mg of long acting nifedipine, six hourly.

Nifedipine can cause postural hypotension; a sudden lowering of blood pressure so the patient has to be warned to get up slowly from a sitting or reclining position. It has also been used in the same dosage to prevent HAPO in people with a past history of this disease.

Frusemide may clear the lungs of water in HAPO and reverse the suppression of urine brought on by altitude. However, Frusemide can also lead to collapse from low volume shock if the victim is already dehydrated. Treatment dosage is 120mg daily.

For more information go to the Mountain Sickness page.