Altitude diseases occur because of a lack of oxygen at high altitudes.
Symptoms include headache, tiredness, irritability, and in more serious cases, shortness of breath, confusion, and even coma.
Doctors diagnose altitude diseases primarily based on the symptoms.
Treatment may include rest, descending to a lower altitude, and sometimes drugs, extra oxygen, or both.
People may prevent these disorders by ascending slowly and sometimes by taking drugs.
As altitude increases, the atmospheric pressure decreases, thinning the air so that less oxygen is available. For example, compared with the air at sea level, the air at 19,000 feet (5,800 meters) contains only half the amount of oxygen. In Denver, which is located about 5,300 feet (1,615 meters) above sea level, the air contains 20% less oxygen.
Most people can ascend to 5,000 to 6,500 feet (1,500 to 2,000 meters) in one day without problems, but about 20% of people who ascend to 8,000 feet (2,500 meters) and 40% who ascend to 10,000 feet (3,000 meters) develop some form of altitude disease. The rate of ascent, highest altitude reached, and sleeping altitude all influence the likelihood of developing the disorder.
The organs most commonly affected by altitude diseases are the
Lungs (causing high-altitude pulmonary edema [HAPE])
The risk of developing altitude illness varies greatly among individuals. But generally, risk is increased by
Risk is greater in people who previously had an altitude disease and in those who normally live at sea level or at very low altitude (below 3,000 feet [900 meters]).
People who have disorders such as diabetes, coronary artery disease, and mild chronic obstructive pulmonary disease (COPD) are not at increased risk for altitude diseases. However, such people may have difficulties with these chronic medical problems at high altitude because of low blood oxygen levels (hypoxemia). Physical fitness is not protective. Asthma does not generally seem to be worse at high altitudes. Also, spending less than a few weeks at higher altitudes (but below 10,000 feet) does not appear to be dangerous for a pregnant woman or the fetus.
The body eventually adjusts (acclimatizes) to higher altitudes by increasing respiration, by producing more red blood cells to carry oxygen to the tissues, and by making other adjustments in the body. Most people can adjust to altitudes of up to 10,000 feet in a few days. Adjusting to much higher altitudes takes many days or weeks, but some people can eventually carry out nearly normal activities at altitudes above 17,500 feet (about 5,300 meters). However, no one can fully acclimatize to long-term residence above that altitude.
Acute mountain sickness is a mild form of altitude disease and is the most common form. It usually does not develop unless altitude is at least 8,000 feet (2,440 meters), but it can develop at lower altitudes in highly susceptible people. Symptoms usually develop within 6 to 10 hours of ascent and often include headache and one or more other symptoms, such as light-headedness, loss of appetite, nausea, vomiting, fatigue, weakness, or irritability. Some people describe the symptoms as similar to those of a hangover. Symptoms usually last 24 to 48 hours. Occasionally, acute mountain sickness progresses to a more severe form of altitude disease known as high-altitude cerebral edema.
HACE is a rare but potentially fatal condition. People with HACE have headache, confusion, and walking that is unsteady and uncoordinated (ataxia). If the disorder is not recognized and treated at an early stage, affected people may lapse into a coma. These symptoms may progress rapidly from mild to life-threatening within a few hours.
HAPE usually develops 24 to 96 hours after a rapid ascent to over 8,000 feet (2,500 meters). HAPE is responsible for most deaths due to altitude disease. People who live at high altitudes may develop HAPE when they return after a brief stay at a lower altitude, a phenomenon called reentry pulmonary edema. Respiratory infections, even minor ones, may increase the risk. Symptoms are worse at night when people lay down and can quickly become more severe if HAPE is not recognized and treated promptly. Mild symptoms usually include a dry cough and shortness of breath after only mild exertion. Moderate symptoms include shortness of breath at rest and a bluish tinge to the skin, lips, and nails (cyanosis). Severe symptoms include gasping for breath, pink or bloody sputum, severe cyanosis, and making gurgling sounds while breathing.
Swelling of the hands, the feet, and, on awakening, the face is common. The swelling causes little discomfort and usually goes away in a few days or with descent.
Headache, without any other symptoms of acute mountain sickness, is also common.
Retinal hemorrhages (small areas of bleeding in the retina at the back of the eye) may develop after ascent to altitudes above 9,000 feet (2,700 meters). These hemorrhages are common above 16,000 feet (5,000 meters). People usually have no symptoms unless the hemorrhage occurs in the part of the eye that is responsible for central vision (the macula). In such cases, people may notice a small blind spot. Retinal hemorrhages resolve over a period of weeks without causing long-term problems. People who develop blind spots in their vision while climbing or trekking at high altitude should descend to lower elevation and seek further evaluation. Reascent to high altitude can be undertaken once the hemorrhage has resolved.
Doctors diagnose altitude diseases based mainly on the symptoms. In people with HAPE, doctors can usually hear fluid in the lungs through a stethoscope. An x-ray of the chest and measurement of the amount of oxygen in the blood can help confirm this diagnosis.
The best way to prevent altitude disease is to ascend slowly. The altitude at which a person sleeps is more important than the maximum height reached during the day. Control of the rate of ascent (called graded ascent) is essential for activity any higher than 8,000 feet (2,500 meters). Above 3,000 meters (10,000 feet), climbers or trekkers should not increase their sleeping altitude by more than 500 meters per day and should include a rest day (sleep at the same altitude) every 3 to 4 nights before they sleep at any higher altitudes. During rest days, day hikes to higher elevations are acceptable as long as people return to the lower level for sleep.
People vary in their ability to ascend without developing symptoms. Thus, a climbing party should be paced for its slowest member.
Acclimatization reverses quickly. If acclimatized people have descended to low levels for more than a few days, they must once more follow a graded ascent when they reascend.
Acetazolamide taken at the start of the ascent can reduce the likelihood of altitude diseases. If taken after the disease has begun, acetazolamide may help lessen symptoms. Acetazolamide should be stopped when descent is initiated or after a few days have been spent at the peak elevation. Dexamethasone can also reduce the likelihood of acute mountain sickness and treat its symptoms.
Taking analgesics such as nonsteroidal anti-inflammatory drugs (NSAIDs) may help prevent high-altitude headache.
Using low-flow oxygen during sleep may also be helpful, but this measure may be difficult to carry out.
People who have had previous episodes of HAPE should be alert for any symptoms of a recurrence and descend immediately if symptoms occur. Some doctors also recommend such people take the drugs nifedipine or tadalafil by mouth.
Avoiding strenuous exertion for a day or two after arrival may help prevent altitude diseases. Heavy alcohol consumption, opioids, and sedatives should be avoided, particularly shortly before sleep. Habitual caffeine drinkers should be aware of the possibility of caffeine-withdrawal headaches if they stop consuming caffeine on their excursion.
Although physical fitness enables greater exertion at altitude, it does not protect against any form of altitude disease. Acetazolamide can be used to improve sleep, which is disturbed for many people traveling to high altitude.
People who have swelling of the hands, feet, and face do not need treatment. The swelling goes away on its own after a few days or following descent. Poor sleep is a common problem at high altitude, even among healthy people, and, by itself, is not a reason to descend to lower elevation.
People with acute mountain sickness must stop their ascent and rest. They should not ascend to higher altitudes until symptoms disappear. Most people with acute mountain sickness improve within a day or two. Acetazolamide or dexamethasone may help relieve symptoms. Acetaminophen or NSAIDs help relieve headache.
If symptoms are more severe, supplemental oxygen should be provided through a face mask or nasal prongs. If supplemental oxygen is unavailable, or if symptoms persist or worsen despite treatment, the person should descend to a lower altitude, preferably 1,650 to 3,200 feet (500 to 1,000 meters) lower.
People with HAPE should descend to a low altitude as soon as possible. Oxygen should be given if it is available. The drug nifedipine may temporarily help by decreasing blood pressure in the arteries to the lungs.
If HACE develops, the person should descend as far down and as soon as possible. Oxygen and dexamethasone should be taken.
When prompt descent to a lower altitude is not possible and people are seriously ill, a hyperbaric bag can be used to buy time. This device consists of a lightweight, portable fabric bag large enough to completely contain a person and a manually operated pump. The person is sealed tightly in the bag, and the bag's internal pressure is then increased using the pump. The increased air pressure simulates a decrease in altitude. The person remains in the bag until symptoms resolve. The hyperbaric bag is as beneficial as supplemental oxygen, which often is not available when mountain climbing, but is not a substitute for descent.