Altitude Sickness

Peter H. Hackett, David R. Shlim

Occurrence

The stresses of the high-altitude environment include cold, low humidity, increased ultraviolet (UV) radiation, and decreased air pressure, all of which can cause problems for travelers. The greatest concern, however, is hypoxia. At 10,000 ft (3,000 m), for example, the inspired PO2 is only 69% of sea-level value. The degree of hypoxic stress depends upon altitude, rate of ascent, and duration of exposure. Sleeping at high altitude produces the greatest hypoxia; day trips to high altitude with return to low altitude are much less stressful on the body.

Acclimatization

The human body adjusts very well to moderate hypoxia, but requires time to do so (Box 2-3). The process of acute acclimatization to high altitude takes 3–5 days; therefore, acclimatizing for a few days at 8,000–9,000 ft before proceeding to higher altitude is ideal. Acclimatization prevents altitude illness, improves sleep, and increases comfort and well-being, although exercise performance will always be reduced compared with low altitude. Increase in ventilation is the most important factor in acute acclimatization; therefore, respiratory depressants must be avoided. Increased red-cell production does not play a role in acute acclimatization.

Risk for Travelers

Inadequate acclimatization may lead to altitude illness in any traveler going to 8,000 ft (2,500 m) or higher. Susceptibility and resistance to altitude illness are genetic traits, and no screening tests are available to predict risk. Risk is not affected by training or physical fitness. Children are equally susceptible as adults; persons >50 years of age have slightly lower risk. How a traveler has responded to high altitude previously is the most reliable guide for future trips but is not infallible. However, given certain baseline susceptibility, risk is greatly influenced by rate of ascent and exertion.
Determining an itinerary that will avoid any occurrence of altitude illness is difficult because of variations in individual susceptibility, as well as in starting points and terrain. Itineraries with a high risk for altitude illness include flying directly to >9,000 ft or rapid hiking ascents, such as climbing Mt. Kilimanjaro. It is best to average no more than 1,000 ft (300 m) ft per day in altitude gain above 12,000 ft (3,660 m).
Examples of high-altitude cities with airports are Cuzco, Peru (11,000 ft; 3,326 m); La Paz, Bolivia (12,000 ft; 3,660 m); and Lhasa, Tibet (12,500 ft; 3,810 m). Travelers flying into these locations may require a period of acclimatization before proceeding higher, and drug prophylaxis may be indicated.
 

Clinical Presentation

Altitude illness is divided into three syndromes:
bulletAcute mountain sickness (AMS)
bulletHigh-altitude cerebral edema (HACE)
bulletHigh-altitude pulmonary edema (HAPE)

Acute Mountain Sickness (AMS)

AMS is the most common form of altitude illness, striking, for example, 25% of all visitors sleeping above 8,000 ft (2,500 m) in Colorado. Symptoms are those of an alcohol hangover: headache is the cardinal symptom, sometimes accompanied by fatigue, loss of appetite, nausea, and, occasionally, vomiting. Headache onset is usually 2–12 hours after arrival at a higher altitude, and often during or after the first night. Preverbal children may develop loss of appetite, irritability, and pallor. AMS generally resolves with 24–72 hours of acclimatization.

High-Altitude Cerebral Edema (HACE)

HACE is a severe progression of AMS and is rare; it is most often associated with pulmonary edema. In addition to AMS symptoms, lethargy becomes profound, with drowsiness, confusion, and ataxia on tandem gait test. A person with HACE requires immediate descent; death from HACE can ensue within 24 hours of developing ataxia if the person fails to descend.

High-Altitude Pulmonary Edema (HAPE)

HAPE can occur by itself or in conjunction with AMS and HACE; incidence is 1/10,000 skiers in Colorado and up to 1 of 100 climbers at >14,000 ft (4,270 m). Initial symptoms are increased breathlessness with exertion, and eventually increased breathlessness at rest, associated with weakness and cough. Oxygen or descent of 1,000 m or more is life-saving. HAPE can be more rapidly fatal than HACE.

Pre-Existing Medical Problems

bulletTravelers with medical conditions, such as heart failure, myocardial ischemia (angina), sickle cell disease, or any form of pulmonary insufficiency, should be advised to consult a physician familiar with high-altitude medical issues before undertaking high-altitude travel.
bulletThe risk for new ischemic heart disease in previously healthy travelers does not appear to be increased at high altitudes.
bulletDiabetics can travel safely to high altitude, but they must be accustomed to exercise and carefully monitor their blood glucose. Diabetic ketoacidosis may be triggered by altitude illness and may be more difficult to treat in those on acetazolamide. Not all glucose meters may read accurately at high altitudes.
bulletMost people do not have visual problems at high altitude. However, at very high altitudes some persons who have had radial keratotomy may develop acute farsightedness and be unable to climb by themselves. LASIK and other newer procedures may produce only minor visual disturbances at high altitudes.
bulletThere are no studies or case reports of harm to a fetus if the mother travels briefly to high altitude during pregnancy. However, it may be prudent to recommend that pregnant women stay at sleeping altitudes of 12,000 ft (3,658 m) if possible. The dangers of having a pregnancy complication in remote, mountainous terrain should also be discussed.

 

References

  1. Hackett PH, Roach RC. High-altitude illness. N Engl J Med. 2001;345(2):107–14.
  2. Hackett PH, Roach RC. High-altitude medicine. In: Auerbach PS, editor. Wilderness medicine 5th ed. Philadelphia: Mosby Elsevier; 2007.
  3. Pollard AJ, Murdoch DR. The high altitude medicine handbook. 3rd ed. Abingdon, UK: Radcliffe Medical Press; 2003.
  4. Hackett PH. High altitude and common medical conditions. In: Hornbein TF, Schoene RB, editors. High altitude: an exploration of human adaptation. New York: Marcel Dekker, Inc.; 2001:839–85.
  5. Strom BL, Schinnar R, Apter AJ, et al. Absence of cross-reactivity between sulfonamide antibiotics and sulfonamide nonantibiotics. N Engl J Med. 2003;349(17):1628–35.
  6. Johnson TS, Rock PB, Fulco CS, et al. Prevention of acute mountain sickness by dexamethasone. N Engl J Med. 1984;310(11):683–6.
  7. Maggiorini M, Brunner-La Rocca HP, Peth S, et al. Both tadalafil and dexamethasone may reduce the incidence of high-altitude pulmonary edema: a randomized trial. Ann Intern Med. 2006;145(7):497–506.