If you will be visiting mountain areas you should be prepared to recognize and respond to the symptoms of altitude illness which are caused by the lower level of oxygen available at high elevations. Although the human body can adjust to changes in altitude, the process (called acclimatization) takes time. Acclimatization is not completely understood, although there is some evidence that suggests genetic factors might play a part in an individual’s response to altitude.
Each person has his or her own “acclimatization line.” Below it you probably won’t experience altitude illness, but going above it causes symptoms to begin. For most people, this line initially lies somewhere near 9,000 feet (2,700 meters), but it can be adjusted by following preventive techniques.
Prevention: The simplest way to avoid or reduce the symptoms of altitude illness is to ascend slowly to give your body time to become accustomed to changes in oxygen concentration. It’s also important to increase your fluid intake to counteract symptoms of dehydration induced by dry mountain air and increased respiratory rate.
Spending the night at or just below one’s acclimatization line gives the body time to adjust. If you begin to feel symptoms of altitude illness, you are probably near your acclimatization line. Once you reach your acclimatization line, or an altitude of 10,000 feet (3,000 meters), it is best to keep your total daily altitude gain under 1,000 feet (300 meters). You can exceed 1,000 feet of altitude during the day’s climb, but you should descend to sleep at an altitude that is no more than 1,000 feet above the previous night’s altitude. Ascending during the day and descending partway to sleep will help you acclimatize more efficiently. Your acclimatization line adjusts, and most people can continue climbing the next day. This is the source of the maxim “climb high, sleep low.”
Symptoms of altitude illness occur during ascent, not descent. If a group tries to push past the limits of its individual climbers, there is a good chance that those who are most susceptible will experience symptoms of altitude illness. If you or a member of your party becomes ill during ascent, you should always assume the problem is due to altitude illness and act accordingly.
Keep a log of the altitude at which your trip begins, the amount gained each day, and the altitude at which you sleep each night. If you become ill, this information will be very important.
Avoid using alcohol or any unnecessary medications since their effects may be increased at high altitudes. Sleeping pills, tranquilizers, and narcotic-based pain relievers, in particular, can cause serious problems at high altitudes because they can decrease breathing rate. Consult with your health care provider about any medications you plan to bring with you.
Three Types of Illness
Acute mountain sickness (AMS) typically appears at altitudes above 8,000 feet (2,400 meters), though illness can begin at elevations as low as 5,000 feet (1,500 meters) in some individuals. Symptoms usually appear within a few hours of ascent, and may include one or many of the following:
- muscle aches
- loss of appetite
- nausea or vomiting
- swelling of the face, hands, and feet
If you experience mild AMS symptoms, limit your activity level and remain at the same altitude for a day or two before resuming the climb. Aspirin or ibuprofen can be used for headache. If symptoms become worse during a day of rest, it is very important to descend until you begin to improve.
Acetazolamide1 (Diamox) has been shown to prevent or lessen AMS symptoms by improving your acclimatization. For prevention of AMS in adults, the recommended dose is 125 mg twice a day (total of 250 mg/day), to be started the day before ascent and continued during ascent and for 24 to 48 hours after reaching your highest altitude. Persons who remain symptomatic after 48 hours may continue taking the drug each evening for several more days, to help them sleep. A 250 mg dose taken twice daily has been effective in treating AMS when given at the onset of symptoms and continued for 1 day after symptoms have cleared. Acetazolamide can also be used in children (5 mg/kg twice daily) for the prevention or treatment of altitude illness if indicated.
Dexamethasone2 is not recommended for the prevention of AMS except under extreme circumstances such as the sudden need to perform a rescue at extreme altitudes. When used for treatment, dexamethasone can improve symptoms long enough for severely ill climbers to descend to safety and medical help, but it is not curative and does not improve acclimatization. The adult dose typically recommended is 4 mg every 6 hours. Dexamethasone is not recommended for prevention of AMS in children as they would not be in the extreme situation noted above, and its use for treatment in children has not been studied.
Additional drugs and oxygen treatment may be necessary, depending on the severity of the illness. Consult your health care provider or travel medicine specialist for specific recommendations about prevention and treatment.
High Altitude Cerebral Edema (HACE) can be thought of as a worsening of AMS symptoms, with the addition of changes in consciousness and/or a loss of coordination as intracranial pressure increases. Persons affected may hallucinate, appear confused, and begin to stumble or stagger. They can have severe headaches and incapacitating fatigue. This is a dangerous form of altitude illness, and it can lead to coma and death.
When used for treatment in adults, dexamethasone2 (usually 4 mg every 6 hours) can often improve symptoms long enough for severely ill climbers to descend to safety and medical help, but it is not curative and does not improve acclimatization. It is crucial for the victim to descend and receive drug and oxygen treatment. Climbers need to watch each other for symptoms, since victims may be unable to grasp the problem. People who have experienced HACE should not be allowed to begin climbing again, even if they have improved. The use of dexamethasone for treatment in children has not been studied.
High Altitude Pulmonary Edema (HAPE) is a buildup of fluid in the lungs that can occur along with HACE or as a separate illness. Like HACE, it is a medical emergency. Those affected will be breathless and very tired when walking and have a sense of fullness or pressure in the chest. Eventually victims will be short of breath even while resting. At this point the illness can rapidly progress to death. Victims must be guided back down and receive drug and oxygen treatment as soon as their illness is recognized as HAPE. They should be kept warm and assisted as much as possible, since exertion will make their condition worse.
Drug treatment in adults often includes 10 mg of nifedipine3 every 8 hours to reduce pressure in the pulmonary artery. Some people have chosen to ascend again after recovering from HAPE, but this is not recommended. The use of nifedipine for treatment in children has not been studied.
Danger signs include severe headache, extreme fatigue, or breathlessness (especially while resting), and any neurological problems such as stumbling, confusion, poor judgment, or changes in consciousness. It is crucial to descend until symptoms begin to diminish if these signs are present.
Flying or Driving to High Altitudes
Flying or driving directly to a mountain destination does not allow the human body enough time to adjust to the altitude. Every attempt should be made to plan your trip to include days spent at transitional altitudes. If you are flying or driving to a high-altitude location, consult with your health care provider before you leave and discuss your need for medications to prevent and/or treat altitude illness. And remember, the same advice that applies to climbers applies to anyone at a high altitude: watch for signs of altitude illness, drink extra water, don’t do too much too fast, and avoid alcohol and unnecessary medications, especially those that decrease breathing rate such as sleeping pills, tranquilizers, and narcotic-based pain relievers.
There is a good chance that those who have had altitude illness once will have it again at high elevations. If you have had altitude problems previously or if you are planning to go to extremely high altitudes, consult your health care provider to discuss your options for prevention and treatment of illness. If you have a preexisting health problem (e.g., heart or lung problems, sickle cell trait or sickle cell disease, or other blood disorder), it is especially important to consult your health care provider. Cardiac or pulmonary evaluation or other types of screening might be needed before travel. Persons with sickle cell trait or sickle cell disease should be aware that even moderate altitudes—such as those encountered in airplane travel—can trigger a sickle cell crisis, and these persons should avoid high altitudes. People with low red blood cell counts could have difficulty adjusting to high altitude, since their oxygen-carrying capacity would already be low. People with too many red blood cells (a condition called polycythemia) could be at risk for blood clots at altitude. Your health care provider can advise you on prevention and treatment options if you have these or other preexisting conditions, and can advise when you should avoid travel to high altitude.
Pregnant women should not trek at high altitude because of the isolation from medical care that would be needed in the event of early labor or complications of pregnancy and because of the rapid drop-off in oxygenation above 12,000 ft or so. There are no data available concerning the risks of altitude on the fetus.
The drugs that are used either for altitude illness prevention or treatment—acetazolamide, dexamethasone, and nifedipine—are Class C drugs; these types of drugs would be given during pregnancy only when the benefit outweighs the potential risk.
- Acetazolamide would not be used in pregnancy to prevent or treat AMS because AMS is not a life-threatening condition.
- Dexamethasone should not be used by any traveler for prevention except in extreme circumstances such as the sudden need to perform a rescue at altitudes beyond tourist destination altitudes, a situation that would not involve pregnant women. Nifedipine is not used for prophylaxis.
- Dexamethasone and nifedipine are used for the treatment of HACE and HAPE in remote high altitude trekking situations, but this is an activity that is not recommended for pregnant women. HACE and HAPE are uncommon at tourist destination altitudes. Oxygen is the primary treatment for these conditions should they occur in pregnant women.
Infants and Children
There are very little data available on the effect of high altitude on young children. Anecdotal opinion is that very young children might be more susceptible to altitude illness than adults. When contemplating taking young children to high altitude, be aware that pre-verbal children will not be able to tell you how they are feeling and should be observed closely for signs that may seem vague, such as increased sleepiness, decreased appetite, or irritability. Children who can report on their symptoms are easier to monitor. (In addition to altitude, small children may have increased problems with cold weather and may be at risk for infectious diseases in a remote area if one is trekking in a developing country.)
The decision to take a child to high altitude in a remote area should not be taken lightly, but can be done safely if the trip is oriented around the child and you are willing to descend readily if you are uncertain as to how your child is doing. There have been no altitude-related deaths among children in more than 30 years of trekking in Nepal.
When indicated, acetazolamide can be used for the prevention or treatment of AMS in children, but dexamethasone and nifedipine are not recommended for use in prevention or treatment of altitude illness in children. (Dexamethasone should not be used by any traveler for prevention except under extreme circumstances such as the sudden need to perform a rescue at extreme altitudes beyond tourist destination altitudes, a situation that would not involve children. The use of dexamethasone for treatment of altitude illness in children has not been studied. Nifedipine is not normally used for prophylaxis, and use of nifedipine for the treatment of altitude illness in children has not been studied.)
1. Acetazolamide (Diamox) may cause tingling in hands and feet or nausea in some people. It is commonly used as a diuretic, and will usually increase urination. Acetazolamide is distantly related to sulfa drugs but persons with sulfa allergy have no increased risk of an allergic reaction when taking acetazolamide. Allergic reactions to acetazolamide are extremely rare, and persons with a history of mild sulfa reactions or rashes can take acetazolamide safely. Risk of an allergic reaction may be increased if you have multiple drug allergies. Persons with a history of lifethreatening reactions to sulfa drugs or multiple drug allergies should receive acetazolamide in acontrolled environment before the trip to see if an allergy exists. Acetazolamide should not be used by persons with kidney or liver disorders, or on high-dose aspirin therapy. (See also “Pregnancy” and “Infants and Children,” above.) Always consult your health care provider for specific recommendations.
2. Dexamethasone is a steroid, commonly used to reduce inflammation. Since its use in altitude illness is usually of short duration, side effects caused by prolonged steroid use do not usually apply. If used for more than 10-14 days, however, it may cause changes in blood sugar, blood pressure, immune system function, and thought processes. (See also “Pregnancy” and “Infants and Children,” above.) Always consult your health care provider for specific recommendations.
3. Nifedipine improves blood flow and reduces the need for oxygen. It is commonly used to relieve heart pain and hypertension. It can cause a drop in blood pressure, which typically makes people feel weak and dizzy. It can also cause headache, nausea, dizziness, and swelling of the legs in some people. (See also “Pregnancy” and “Infants and Children,” above.) Always consult your health care provider for specific recommendations.
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