High-Altitude Illness


This fact sheet provides information on high-altitude illnesses, including acute mountain sickness (AMS), high-altitude cerebral edema (HACE), and high-altitude pulmonary edema (HAPE). Those traveling to high altitudes should be aware of the symptoms and treatments for high-altitude illnesses.


Acute Mountain Sickness (AMS) 

Acute mountain sickness is a group of symptoms that occurs when an individual ascends too quickly. Acute mountain sickness is extremely common at high altitudes (75% of people will have mild symptoms at altitudes over 10,000 feet), but it is much less severe than HACE and HAPE. The severity of AMS depends on change in altitude, rate of ascent, and individual variability. It is important to note that signs and symptoms experienced at around 6,500 feet and above are likely due to AMS and should be treated as such. However, at altitudes below 6,500 feet, these signs and symptoms may be the result of another condition, such as heat illness or dehydration. 

Symptoms of AMS 

Symptoms of AMS may include mild headache, loss of appetite, nausea, dizziness, insomnia, and fatigue. These symptoms will decrease over time as the body acclimates to the altitude. Acclimatization usually takes between 2 and 4 days. If symptoms get worse and start to resemble those of HACE or HAPE, the person should immediately go to a lower altitude (between 2,000 and 4,000 feet) and receive proper medical treatment. 

What to Do if a Person Is Exhibiting Symptoms of AMS 

Although AMS is not life threatening and the symptoms are often mild and manageable, it can develop into HACE or HAPE (life-threatening conditions) if not immediately treated. It may be necessary to descend to a lower altitude or to simply stop at the current altitude to wait for improvement before going higher. If conditions worsen, immediately move to a lower elevation (descend at least 1,000–2,000 feet). Aspirin or acetaminophen can be taken for headache pains. If the afflicted person has prescribed medication, this can be self-administered, and symptoms will usually diminish after 12 to 24 hours. 

High-Altitude Cerebral Edema (HACE) 

High-altitude cerebral edema is the result of the swelling of brain tissue. Little is known about the exact physiological processes that occur that lead to the fluid buildup in the brain. HACE is a more severe form of acute mountain sickness (AMS). 

Symptoms of HACE 

Symptoms of HACE include extreme fatigue, loss of coordination, severe headache, unusual changes in personality (such as violence or laziness), drowsiness, nausea, and confusion. More severe symptoms may include seizures, coma, and stroke. HACE can be fatal if not treated promptly after symptoms are observed. 

What to Do if a Person Is Exhibiting Symptoms of HACE

The safest and most effective form of treatment for HACE is to immediately descend to a lower altitude (between 2,000 and 4,000 feet). Once at a lower altitude, the individual should be taken to a medical facility for proper treatment. 

High-Altitude Pulmonary Edema (HAPE) 

High-altitude pulmonary edema is the result of fluid buildup in the lungs. Fluid from the body leaks into the lungs because of the lower air pressure at higher altitudes and because of physiological changes in the body that are not completely understood. The fluid builds up in the alveolar regions of the lung, where oxygen from the air enters the bloodstream. The presence of this fluid inhibits the exchange of oxygen. There is also less oxygen available in the air at higher altitudes, which can contribute to a lack of oxygen in the blood. As this condition becomes more severe, the amount of oxygen that is in the blood decreases significantly, causing a wide variety of problems, including impaired brain function and even death. The condition may occur in people who rapidly ascend to altitudes higher than 8,000 feet, especially when they are exerting themselves. 

Symptoms of HAPE 

Symptoms of HAPE include extreme fatigue, breathlessness (even at rest), shallow and fast breathing, coughing, chest tightness, visual impairment, lethargy, and blue or gray lips or fingernails. The person may also be confused or act irrationally because of the lack of oxygen reaching the brain. 

What to Do if a Person Is Exhibiting Symptoms of HAPE 

A person exhibiting symptoms of HAPE, a life-threatening condition, should immediately descend to a lower altitude (between 2,000 and 4,000 feet). Once at a lower altitude, the individual should be taken to a medical facility to receive proper treatment. 

Those at Risk for High-Altitude Illness 

Anyone traveling to high altitudes is at risk for AMS, HACE, and HAPE. An increased level of physical fitness does not provide protection. It is important to realize that it is not the altitude itself but the change in altitude that accounts for most of the symptoms. The rate of ascent is also a risk factor for developing high-altitude illness—the more rapid the ascent, the higher the risk. Biological, genetic, known cardiac and pulmonary problems, and lifestyle variations can also play a role in the severity and onset of high-altitude illness. Any person who has experienced high-altitude illness in the past should avoid traveling to high altitudes. 

Prevention and Treatment of High-Altitude Illness 

A slow, gradual ascent that allows the body to acclimate in stages over a few days will minimize the risk of developing high-altitude illness. Avoiding overexertion, decreasing salt intake, and increasing dietary carbohydrate intake may also reduce the risk. The prescription medication acetazolamide may also be used as a preventative treatment for AMS. Several reputable organizations recommend not traveling higher than 8,000–9,000 feet above sea level from a low altitude in one day. It is helpful to spend a few days acclimatizing at 8,000 or 9,000 feet before continuing an ascent. A person’s sleeping altitude should increase by no more than 1,600 feet per day after reaching 9,000 feet. A person should also try to spend a day or two without ascending for every 3,300 feet of ascent. Another way to reduce the risk of high altitude illness is to take a day trip to a higher altitude and return to a lower altitude to sleep. 

Early detection of high-altitude illness is essential for effective treatment. Because HACE and HAPE can be life-threatening conditions, it is imperative that a person experiencing symptoms of HACE or HAPE immediately descend to a lower altitude (between 2,000 and 4,000 feet). The person should also be taken to a medical facility to receive proper treatment, which may include oxygen therapy and the prescription medications acetazolamide and nifedipine. 

It is also important to note that those with certain preexisting medical conditions may need to refrain from traveling to or spending long amounts of time at high altitudes. Before planning a trip to a high altitude, consult a doctor if you have a heart or lung disease, you have diabetes, or you are pregnant. 

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