Altitude sickness represents a spectrum of disorders that result from decreased availability of oxygen at high altitudes. Acute mountain sickness (AMS) is the mildest of these disorders; high-altitude cerebral edema (HACE) and high-altitude pulmonary edema (HAPE) represent more severe forms.
As altitude increases, the partial pressure of oxygen in inspired air decreases. Since partial pressure is the “driving force” that pushes oxygen through pulmonary capillary walls, less oxygen is available to the tissues of the body at higher altitudes.
Although travel to 2000 m (6500 ft) is well tolerated by most individuals, 20% of those ascending to 2500 m (8,000 ft) and 40% of those climbing to 3000 m (10,000 ft) will develop some form of altitude sickness. (The Merck Manual, 18th Edition 2006:2613-16)
Pathophysiology of Altitude Sickness
Hypoxia stimulates the release of various hormones and causes compensatory elevations of capillary pressures, with resultant capillary leakage and edema. Such physiologic adaptation can initiate a vicious cycle that aggravates the underlying pathology of AS: In the lungs, fluid within the alveoli (pulmonary edema) further impairs oxygen exchange; in the brain, tissue swelling triggers additional adaptive mechanisms that increase swelling.
Signs and Symptoms of Altitude Sickness
Signs and symptoms of altitude sickness develop over several hours to days.
- AMS: Headache, fatigue, loss of appetite, sleep disturbance, nausea, vomiting.
- HACE: Headache, confusion, drowsiness, difficulty walking (a reliable diagnostic sign), stupor, and coma.
- HAPE: Difficulty breathing, dry cough, and decreased exercise tolerance that can progress to severe respiratory distress with pink or bloody sputum, cyanosis, and coma.
- HAPE and HACE can occur together; while both can be fatal within 24 hours of symptom development, HAPE can be more rapidly fatal than HACE.
Risk Factors for Altitude Sickness
- Quick ascents
- Higher maximum altitudes
- Higher sleeping altitudes
- Exertion
- Cold
- Previous episodes of AS
- Alcohol use
- Age (young children and young adults are MORE susceptible)
- Altitude of residence (those who normally live at low altitudes are at greater risk)
- Physical fitness is NOT protective
- Chronic illnesses such as diabetes, coronary artery disease, sickle-cell disease, or COPD do not increase the risk of AS, but hypoxia may aggravate these conditions
Preventing Altitude Sickness
- Graded ascent (acclimatization): For any planned activity above 8000 feet, climbers should increase sleeping altitude by 1000 ft daily after spending the first two to three nights near 8000 feet.
- Water: Drinking extra water offsets losses incurred from breathing dry air at altitude.
- Diet: Consume small, frequent meals that are high in easily digested carbohydrates. Avoid extra salt.
- Medications: Acetazolamide (Diamox) 125 mg every 8-12 hours (or 500 mg sustained-release once daily), started on the day before ascent, acidifies the blood and increases ventilation. For those with a history of prior HAPE, nifedipine 20-30 mg twice daily is preventive. Ginkgo biloba, Viagra, and inhaled salmeterol have shown promise in some studies, but research is lacking.
- Alcohol reduces ventilation during sleep; it should be avoided
Treating Altitude Sickness
- AMS: Halt ascent; rest until symptoms resolve. Ensure adequate fluid and calorie intake. Acetazolamide 250 mg twice daily may relieve symptoms. If symptoms worsen or are severe, administer dexamethasone 4-8 mg every 6 hours and descend 500 to 1000 meters.
- HACE and HAPE: Immediately descend to low altitude. Oxygen, medications, and pressurization in a hyperbaric (Gamow) bag may help, but these cannot substitute for descent. For HAPE, nifedipine 20 mg sublingually followed by 30 mg orally is beneficial. For HACE, dexamethasone is helpful. (Shlim D. Travelers’ Health-Yellow Book, Centers for Disease Control and Prevention 2007;Ch6[12])
Travelers who fly, climb, or drive to high altitudes should be aware of the risks of altitude sickness. Early recognition of symptoms is the key to successful treatment and recovery.
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