Altitude sickness may develop in travelers who ascend rapidly to altitudes greater than 2500 m, including those in previously excellent health. Being physically fit in no way lessens the risk of altitude sickness. Those who have developed altitude sickness in the past are prone to future episodes. The risk increases with faster ascents and higher altitudes. Symptoms of acute mountain sickness, the most common form of the disorder, may include headaches, nausea, vomiting, dizziness, malaise, insomnia, and loss of appetite. Severe cases may be complicated by breathlessness and chest tightness, which are signs of pulmonary edema (fluid in the lungs), or by confusion, lethargy, and unsteady gait, which indicate cerebral edema (brain swelling).
Altitude sickness may be prevented by taking acetazolamide 125 or 250 mg twice daily starting 24 hours before ascent and continuing for 48 hours after arrival at altitude. Possible side-effects include increased urinary volume, numbness, tingling, nausea, drowsiness, myopia and temporary impotence. Acetazolamide should not be given to pregnant women or anyone with a history of sulfa allergy.
For those who cannot tolerate acetazolamide, an alternative is dexamethasone, which has been shown to prevent acute mountain sickness and high-altitude cerebral edema (but not pulmonary edema). The usual dosage is 4 mg four times daily. Unlike acetazolamide, dexamethasone must be tapered gradually upon arrival at altitude, since there is a risk that altitude sickness will occur as the dosage is reduced. Dexamethasone is a steroid, so it should not be given to diabetics or anyone for whom steroids are contraindicated. For those at risk for high-altitude pulmonary edema, one option is to take oral nifedipine 10 or 20 mg every 8 hours. A newer treatment is prophylactic inhalation of 125 mcg of salmeterol (Serevent)every 12 hours, which was recently shown to reduce the risk of high-altitude pulmonary edema in those with a prior history of this disorder. (See C. Sartori et al, New England Journal of Medicine; 2002;346:1631-6).
Limited evidence indicates that an herbal remedy, gingko biloba, may prevent altitude sickness when started before ascent. The usual dosage is 100 mg every 12 hours.
Other measures to prevent altitude sickness include
- Ascend gradually or by increments to higher altitudes
- Avoid overexertion
- Eat light meals
- Avoid alcohol
The symptoms of altitude sickness develop gradually so that, with proper management, serious complications can usually be prevented. If any symptoms of altitude sickness appear, it is essential not to ascend to a higher altitude. If the symptoms become worse or if the person shows any signs of cerebral or pulmonary edema, such as breathlessness, confusion, lethargy, or unsteady gait, it is essential to descend to a lower altitude. A descent of 500-1000 meters is generally adequate except in cases of cerebral edema, which may require a greater descent. Travelers should not resume their ascent until all symptoms of altitude sickness have cleared. Supplemental oxygen is helpful if available. Acetazolamide, dexamethasone, and nifedipine may all be used to treat altitude sickness as well as prevent it. In most cases, acetazolamide is recommended as prevention, and dexamethasone and nifedipine are reserved for emergency treatment. Nifedipine is preferable to dexamethasone for high-altitude pulmonary edema.
Travel to high altitudes is generally not recommended for those with a history of heart disease, lung disease, or sickle cell disease. It is also not recommended for pregnant women.
From "International Travel and Health" (WHO)
Environmental health risks
From the Centers for Disease Control (CDC)
From Health Canada
Statement on high altitude illnesses
From the National Travel Health Network and Centre (U.K.)