Many Americans will head to the National Parks and mountain resorts of the West this summer and, unfortunately, some of their vacations will be marred by altitude sickness. This common malady is triggered by an impaired ventilatory response to hypoxemia, an increased blood flow to the brain, increased blood pressure in the lungs and an altered acid-base state, especially in the brain and spinal fluid. The risk for developing all forms of altitude sickness is increased by a past history of altitude-related illness, a rapid ascent (>1000 feet/day), a home elevation under 3000 feet, age under 50 years and by strenuous activity prior to acclimation; the altitude at which one sleeps (while in the high country) also correlates with the risk level.
Acute mountain sickness, the most common and least serious form of altitude-related illness, is generally characterized by a mild headache, nausea, fatigue, dizziness and insomnia; in addition to the risk factors listed above, obesity predisposes to this disorder. Symptoms of acute mountain sickness develop over 2-3 hours and often persist for 2-3 days. Preventive measures include a slow ascent, adequate hydration (including a reduced intake of caffeine and alcohol), limited physical exertion for the first few days and the use of acetazolamide (a prescription medication that should be started 2 days before reaching high altitude).
More severe forms of altitude sickness include high altitude pulmonary edema (HAPE) and high altitude cerebral edema (HACE). The former, caused by fluid accumulation in the lungs, usually develops after rapid ascent to 10,000 feet or more and tends to occur within 48 hours. HACE, caused by brain swelling, is relatively rare and generally develops at elevations above 14,000 feet; a gradual onset of headache, confusion and ataxia (impaired coordination) is typical. Both HAPE and HACE are medical emergencies, treated with rest, oxygen administration, a descent to lower altitude and professional intervention. Persons planning high altitude climbs should discuss the preventive use of nifedipine or dexamethasone with their physician.