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Altitude sickness

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Overview of altitude sickness

Altitude sickness (AS) or acute mountain sickness, is a potential problem for people who travel each year to altitudes exceeding 8,000 feet. It is rare a problem for 300 million people in the world who live at high altitudes, due to the phenomenon of acclimatization. Proper acclimatization can prevent altitude sickness.

While one study states that virtually all people traveling to an altitude above one mile (5,280 feet) will experience some symptoms of altitude sickness.1 According to the other study, only 25% of those who travel above 8,500 feet will develop altitude sickness symptoms.2 Yet another study states that altitude sickness is predominantly seen in those who spend more than 8 h at an elevation above 10,000 feet.3 However, all agree that the incidence and severity of altitude sickness are directly proportional to the altitude.

Causes of altitude sickness

Hypoxia or insufficient oxygen to the tissues is the root cause of altitude sickness.

The absolute percentage of oxygen in the air is the same, but as altitude increases, the number of molecules in the specific volume of air decreases.4

At sea level, the arterial oxygen partial pressure is 90–95 mmHg and oxygen saturation is 97%. The figures fall to 40 mmHg and 71%, respectively at 18,000 feet above sea level (prior to eventual acclimatization).

As the patient’s arterial partial pressure of oxygen begins to fall, the body attempts to compensate, by the process of hyperventilation, which helps the patient adapt, also producing water loss and decreased arterial partial pressure of carbon dioxide. Respiratory alkalosis and nocturnal periodic breathing occur. Tachycardia, hypertension, and increased venous tone develop.

Eventually, as the patient becomes acclimatized, the blood becomes thicker, and the percentage of red cells rises from 45% to over 50%.5

Symptoms of altitude sickness

Simple altitude sickness is usually presented as the most minor problem due to altitude.

The more severe problems are

  • high altitude pulmonary edema (HAPE)
  • and high altitude cerebral edema (HACE).

The group of experts participating in the 7th International Hypoxia Symposium in 1991 in Canada,6 defined altitude sickness as a syndrome occurring in the setting of a recent gain in altitude, consisting of headache and at least one of the following:

  • gastrointestinal symptoms, such as anorexia, nausea or vomiting,
  • fatigue or weakness, dizziness or lightheadedness, and
  • difficulty sleeping.

Symptoms that may indicate life-threatening altitude sickness include:

  • HAPE
  • persistent dry cough
  • fever
  • shortness of breath even when resting
  • HACE
  • headache that does not respond to analgesics
  • unsteady gait
  • increased vomiting
  • gradual loss of consciousness.

Management of altitude sickness

Partners should observe each other for potential danger signs, such as

  • Severe headache,
  • Persistent coughing,
  • Skipping meals,
  • Acting in an antisocial manner,
  • Frequent stumbling or losing footing,
  • Refusing to drink,
  • And apparent inability to take part in the normal activities of the group.

The severely affected patient must be moved to a lower altitude. A descent of 2,000–3,000 feet may be required. Partners must remember that altitude sickness often causes disordered thinking and impaired judgment. Left alone, the patient can rapidly progress into the unconsciousness within 12–24 h.4

Drug Therapy for altitude sickness

Acetazolamide has been beneficial in preventing altitude sickness, in a dose of 250–1,000 mg/day starting 12–24 h before the high-altitude exposure and continuing for 3–4 days.2 It hastens acclimatization and reduces the risk and severity of altitude sickness.1

Dexamethasone may also be helpful in treating many symptoms of altitude sickness and managing cerebral edema.5 It is not an alternative to acetazolamide since it does not affect respiration and does not speed acclimatization. High dosages are required, which lead to unpleasant adverse reactions.

Altitude sickness and Medical Conditions

The following conditions do not worsen the risk of altitude sickness:

  • Obesity
  • Hypertension
  • Mild emphysema
  • Coronary artery disease
  • Chronic illnesses, such as cardiac and pulmonary conditions if well-controlled

Problems do arise in patients with:

Prevention of altitude sickness

  • A slow ascent is essential.
  • ‘Climb high, sleep low’: Travelers should spend two nights at the same altitude every three days, and sleep at least 460 feet lower than the highest altitude climbed during the day.
  • Travelers should avoid alcohol, sedatives, smoking and excess stress.
  • Travelers should increase their fluid intake for the first several days.
  • High-carbohydrate diets should be maintained, as carbohydrates allow the body to use oxygen more efficiently at higher altitudes.
  • Fat and sodium intake should be limited.


1. Procelli MJ, Gugelchuk GM. A trek to the top: A review of acute mountain sickness. J Am Osteopath Assoc. 1995; 95(12): 718–720.

2. Harris MD, Terrio J, Miser WF, Yetter JF 3rd. High-altitude medicine. Am Fam Physician. 1998; 57(8): 1907–1914, 1924–1926.

3. Bratton RL. Advising patients about international travel. Postgrad Med. 1999; 106(1): 57–64.

4. Reynolds SE. The illness of ascent: Acute mountain sickness. J Am Acad Nurse Pract. 1997; 9(11): 527–531.

5. Coote JH. Medicine and mechanisms in altitude sickness. Sports Med. 1995; 20(3): 148–159.

6. Anononymous. The Lake Louise Consensus on the Definition of Altitude Illness. http://www.high-altitude-medicine.com/AMS-LakeLouise.html.

Written by: healthplus24.com team

Date last updated: December 10, 2014

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