What Is It?
At higher altitudes, the pressure of the air around you (barometric pressure) decreases so there is less oxygen in surrounding air. People can live comfortably at moderately high altitudes, but the body must make some adjustments, and this takes time. If you ascend to altitudes above 8,000 feet, you will be in danger of developing uncomfortable or dangerous symptoms from the change in altitude.
Symptoms of altitude sickness that are not life threatening are called acute mountain sickness. Mountain climbers on any high mountain and skiers in high-altitude locations such as Colorado are at risk of developing acute mountain sickness. Symptoms from acute mountain sickness improve if you descend to lower altitude quickly. For very mild symptoms, a delay before further climbing may be enough to allow symptoms to go away.
Acute mountain sickness is the least dangerous of several kinds of altitude illnesses that can occur. This sickness affects close to half of all people who begin near to sea level and climb to 14,000 feet of elevation without scheduling enough rest time.
Symptoms that develop at high altitude should be taken very seriously, since some altitude problems can develop into fatal illnesses. One dangerous reaction to high altitude is a condition called high-altitude cerebral edema (HACE), in which the brain accumulates extra fluid, swells and stops working properly. A related illness, high-altitude pulmonary edema (HAPE), can occur with or without warning symptoms that signal altitude sickness. HAPE causes fluid to enter the lungs. A type of altitude sickness called high-altitude retinal hemorrhage (HARH) can cause eye damage. Coma and death are the most serious consequences of altitude sickness.
Altitude sickness is more likely to occur in people who have a previous history of altitude sickness. It is more likely if you climb quickly, if you exercise vigorously during your first few days of altitude exposure, and if you have been living at low elevation prior to your climb. Obesity appears to increase the risk for altitude sickness. Genetics may also put some people at increased risk, particularly for high altitude pulmonary edema (HAPE).
Symptoms
As your body makes normal adjustments to adapt to a high altitude, you may experience a few symptoms that are bothersome but are not cause for concern. They include rapid (but still comfortable) breathing, shortness of breath with strenuous exercise, occasional short pauses in breathing while you sleep, and frequent urination. The last two symptoms are caused by a low carbon dioxide level, which triggers adjustments in the brain and kidney.
More serious symptoms are caused by low levels of oxygen in the blood and adjustments that are made by your circulation system.
Acute mountain sickness usuallycauses symptoms at least 8 to 36 hours after ascent.
Symptoms of acute mountain sickness can include:
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Headache that is not relieved by over-the-counter pain medicine
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Nausea or vomiting
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Dizziness or lightheadedness
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Weakness or fatigue
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Difficulty sleeping
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Loss of appetite
High-altitude cerebral edema is considered by many experts to be an extreme form of acute mountain sickness. It usually develops after symptoms of acute mountain sickness. Symptoms of this more severe altitude disease may not be noticed immediately because the illness can begin during the night. Because this low-oxygen injury affects the brain and thought process, a person with high-altitude cerebral edema may not understand that symptoms have become more severe until a traveling companion notices unusual behavior.
Symptoms may include:
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Worsening headache and vomiting
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Walking with a staggering gait
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Confusion
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Exhaustion
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Visual hallucinations (seeing things that are not real)
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Changes in the ability to think
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Changes in normal behavior
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Coma (in advanced cases)
High-altitude pulmonary edema, which is the lungs' response to an increase in altitude, may occur with or without other symptoms of altitude illness. A low oxygen concentration can trigger blood vessels in the lungs to constrict (tighten), causing a higher pressure in the lung arteries. This causes fluid to leak from the blood vessels into the lungs. Symptoms of high-altitude pulmonary edema commonly appear at night and can worsen during exertion.
Symptoms of high-altitude pulmonary edema include:
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Chest tightness or fullness
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Extreme fatigue
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Inability to catch your breath, even when resting
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Blue or gray lips and fingernails
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Coughing, which may produce pink frothy fluid
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Fever (temperature is above normal but is less than 101° Fahrenheit)
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Noises when breathing, such as rattling or gurgling sounds
High-altitude retinal hemorrhage can occur with or without symptoms. It usually is not noticeable unless the area of the eye that provides the most detailed vision (the macula) is involved.
Blurred vision is the main symptom of high-altitude retinal hemorrhage.
Diagnosis
You must be able to recognize the early symptoms of altitude sickness, and you should watch carefully for symptoms when you are at risk because altitude illnesses can be life threatening.
If headache is your only symptom, you should stop climbing and take a mild pain reliever. If you have a headache that does not go away or if you have other symptoms that suggest acute mountain sickness, this illness can be diagnosed without tests.
High-altitude cerebral edema can make it difficult to walk a straight line, and can lead to changes in thinking, hallucinations or an unexplained change in personality. If a person has these symptoms at high altitude, you should assume that the person has high-altitude cerebral edema. A person with these symptoms should descend immediately and seek medical care. Once a person with high-altitude cerebral edema has been transported to a medical center, a magnetic resonance imaging (MRI) scan may be done to confirm the cause of the symptoms. An MRI can show brain swelling.
Recognizing high-altitude pulmonary edema can be difficult in its early stages because fatigue may be the only sign. Symptoms that should be of concern include difficulty exercising, dry cough, rapid heart rate (more than 100 beats per minute), and shortness of breath while resting. Listening to the lungs with a stethoscope may reveal a crackling noise with each breath. If blood oxygen levels were measured, they would be lower than expected for your altitude. X-rays may show signs of fluid filling one or more areas within the lungs, giving an appearance that is similar to pneumonia.
High-altitude retinal hemorrhage can be diagnosed by a doctor who examines the eye with a hand-held instrument called an ophthalmoscope.
