Article from August, 2016

by Michael J. Manyak, MD, MED ‘92

Altitude Sickness Mike Manyak

Every year spring brings with the thaw a spate of activities at higher altitudes and prompts questions about altitude illness. Serious mountaineers begin to peer skyward while seasons open at popular travel destinations such as Machu Picchu, Kilimanjaro, and Everest Base Camp. Altitude illness results from low oxygen levels (hypoxia) which occur with increasing altitude. For example, the oxygen content in air at 10,000 feet is 69 percent of that at sea level. Compounding the effects of hypoxia for travelers to these heights are cold temperatures, low humidity, decreased air pressure, and increased ultraviolet radiation exposure. These factors can also affect travelers to less remote but elevated sites like Denver, La Paz, Quito, and Addis Ababa.

Human physiology can adapt to these changes but it requires time to adjust though the body is incapable of permanent acclimatization above 17,500 feet. Problems with altitude occur for those who do not have the time or inclination to acclimate to the new height. Travelers who fly into high-altitude destinations directly from lower altitudes should spend three to five days before ascending beyond 8000 feet and spend an extra day for every 3300 feet of higher ascent. It is also recommended to ascend no more than 1500 feet per day.


There is significant variability in individual ability to acclimatize, likely related to genetic differences, but no simple screening tests predict the risk of developing altitude illness for a particular individual. Risk is not affected by training or physical fitness and children are as susceptible as adults. The incidence of altitude illness increases in those with previous history of altitude illness, obesity, and slightly increases in females but does not increase for those who smoke or use oral contraceptives and is somewhat decreased in those over age 50. Maximum overnight altitude and days of acclimatization are also predictors (Croughs, J Travel Med, 2011). Travelers with cardiac and respiratory conditions or diabetes should consult a medical provider familiar with high altitude issues before high-altitude travel.

Altitude Illness

Altitude illness has three syndromes: acute mountain sickness (AMS), high-altitude cerebral edema (HACE), and high-altitude pulmonary edema (HAPE). HACE is a severe progression from AMS while HAPE can occur by itself or in conjunction with AMS or HACE.

Gradual ascent is the safest method of prevention for all forms of altitude illness. It is important to limit exertion and avoid alcohol and sedative medications for the first few nights at high altitude. It is very important to remain hydrated.

The most commonly used medication for prevention of AMS is acetazolamide (Diamox) which is about 75 percent effective to prevent AMS in travelers who cannot gradually ascend. A physician familiar with this medication should prescribe, determine dose, and discuss side effects and allergies. Acetozolamide should be taken from 24 hours before ascent to at least 2 days after reaching altitude. Although less effective, acetazolamide can be used to lessen symptoms once AMS has begun.


Many travelers to high altitude experience temporary headache, fatigue, difficulty breathing with exertion, and sleep disorders. AMS symptoms are similar but more pronounced and include headache, fatigue, loss of appetite, nausea, and vomiting which typically begin within 12 hours of arrival at high altitude and usually subside after 1 to 3 days of acclimatization. AMS is commonly confused with other conditions like viral “flu”, hangover, dehydration, or medication effect. Importantly, travelers with AMS will not improve with hydration or while at rest and should not continue to ascend until symptoms have resolved.

Treatment of mild AMS includes rest and to stop ascent, symptomatic treatment with analgesics, and descent without improvement. More severe AMS requires the initiation of acetazolamide, use of oxygen, possible use of dexamethasone 4mg every 6 hours, and immediate descent. A hyperbaric pressure bag is also useful if available and very desirable if descent is delayed. Such a device can provide the same effect as a 5000 foot descent.


HAPE is a severe consequence of altitude illness from fluid in the lungs. HAPE is the most common cause of death related to high altitude, usually occurs within the first 4 days of ascent, and is easily reversed if recognized and treated. Symptoms of HAPE include difficulty breathing with exertion and at rest, persistent dry cough, and weakness.

The most effective treatment of HAPE is immediate descent. While that is being arranged, keep the patient warm and provide oxygen if available. Dexamethasone should be used for severe or worsening cases. Nifedipine 10mg initially and then every 4 hours depending on response is also useful. Use of a hyperbaric pressure bag is advised if available.


HACE is a rare but severe consequence of altitude illness that causes swelling of the brain. Symptoms of HACE include extreme fatigue, drowsiness, confusion, and loss of coordination. HACE is often confused with AMS in its early stages and usually takes 1 to 3 days to develop from AMS but can develop more quickly in those with HAPE. If HACE develops, the individual must immediately descend to a lower altitude or risk death.

Treatment for HACE is immediate descent or evacuation, oxygen, dexamethasone, and hyperbaric therapy if descent is delayed.


This article was published in The Explorers Journal


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