Acute Altitude Illness: Updated Prevention and Treatment Guidelines from the Wilderness Medical Society
Am Fam Physician. 2020 Apr 15;101(8):505-507.
Author disclosure: No relevant financial affiliations.
Key Points for Practice
• Gradually increasing sleeping altitude is the best way to prevent altitude illness. Staged ascent and preacclimatization to hypoxia also reduce risk.
• Acetazolamide and dexamethasone can be used to prevent acute mountain sickness and high altitude cerebral edema, but only acetazolamide aids in acclimatization.
• The most important treatment for altitude illness is descent of 1,000 to 3,300 ft, with supplemental oxygen if available.
From the AFP Editors
Acute altitude illness comprises acute mountain sickness (AMS), high altitude cerebral edema (HACE), and high altitude pulmonary edema (HAPE). Symptoms of AMS, the most common form of altitude illness, include headache, nausea, vomiting, fatigue, dizziness, and insomnia. If not appropriately treated, AMS can progress to life-threatening HACE or HAPE, which can present together or separately. Although HACE presents with similar symptoms as AMS, the cerebral edema can lead to ataxia, confusion, or altered mental status. HAPE is characterized by reduced exercise tolerance, exertional dyspnea, and cough, followed by dyspnea at rest, cyanosis, and productive cough with pink frothy sputum.
Unacclimatized people are at high risk of acute altitude illness when ascending above 8,200 ft (2,500 m), but AMS can occur as low as 6,500 ft (2,000 m). HACE is typically encountered at higher elevations unless presenting with HAPE. The Wilderness Medical Society does not use specific altitude thresholds for diagnosis.
Because the risk of acute altitude illness depends on acclimatization, sleeping altitude is more important than altitude reached while awake.
People without a history of AMS who do not sleep above 9,200 ft (2,800 m) are at low risk of AMS. Regardless of AMS history, people who allow at least two days to ascend to a sleeping altitude of 8,200 to 9,800 ft (2,500 to 3,000 m) are at low risk if they sleep no more than 1,600 ft (500 m) above the previous night's altitude and take a day to acclimatize after every increase of 3,300 ft (1,000 m) in sleeping altitude.
People with a history of AMS who make a one-day ascent to a sleeping altitude of 8,200 to 9,200 ft have a moderate risk of AMS. Those without a previous episode who make a one-day ascent to a sleeping altitude above 9,200 ft also have a moderate risk. Regardless of AMS history, people who ascend to a sleeping altitude above 9,800 ft are at moderate risk if they sleep more than 1,600 ft above the previous night's altitude but take a day to acclimatize after every increase of 3,300 ft in sleeping altitude.
People with a history of AMS who make a one-day ascent to a sleeping altitude above 9,200 ft have a high risk of developing AMS. All people with a history of HACE or HAPE are at high risk of AMS, regardless of sleeping elevation or rate of ascent. Regardless of AMS history, all people are at high risk of AMS if they: (1) make a one-day ascent to a sleeping altitude above 11,500 ft (3,500 m); (2) make extremely rapid ascents (e.g., climbing Mt. Kilimanjaro [19,341 ft (5,895 m)] in fewer than seven days); or (3) ascend to a sleeping altitude above 9,800 ft, then sleep more than 1,600 ft above the previous night's altitude without allowing a day off to acclimatize.
Prevention of AMS and HACE
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This series is coordinated by Sumi Sexton, MD, editor-in-chief.
A collection of Practice Guidelines published in AFP is available at https://www.aafp.org/afp/practguide.
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