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High Altitude Medical Advice forTravelers

The following information and guidelines will hopefully help the traveler prevent and treat AMS and its complications. All travelers planning to ascend to altitudes greater than 8,000 feet should read and understand these guidelines.


Types of High Altitude Travel:

People can be exposed to high altitude in different ways. Skiing or hiking in resort town in the mountains at altitudes ranging from 4,000 feet to 10,000 feet. Mountain climbers may sleep at higher altitudes at a climber's hut, and may go as high as 14,000 to 15,000 feet during a day's climb. However, the climbers generally return to a lower altitude to sleep.

Some travel destinations, such as La Paz, Bolivia, Lhasa, Tibet, or Cuzco, Peru allow one to travel to relatively high altitudes (11,000 to 12,500 feet) without hiking. It seems that being transported passively to high altitude is less likely to induce altitude illness as quickly as hiking to the same height. However, in many of these destinations descent can be impossible to arrange quickly, as the only way down may be a once daily flight.

Trekking in the Himalayas brings people to high altitude for longer periods of time than in most other situations, and the risk of dying from altitude sickness is consequently higher in this region.

Epidemiology of Altitude Illness

Mild altitude symptoms have been documented at the relatively low altitudes of 4,000 to 6,000 feet, although serious syndromes are rarely seen below 9,000 to 10,000 feet.

The problem of approaching certain high altitude cities gradually can present as a logistic problem. With some itineraries there is no way to approach the altitude gradually. Lhasa, Tibet (12,500 feet) can be reached by air only from airports that are at 4,300 feet. If one drives to Lhasa from Katmandu, one gets to a higher altitude even more quickly than flying.

Trekking in the Himalayas affords the opportunity to acclimatize gradually. However, airports and helipads in the high mountains have allowed people to go to altitude more quickly than before. Altitude illness affects up to 50% or more of trekkers on popular high altitude routes. The death rate from altitude sickness among trekkers in Nepal is about one in 30,000 trekkers, which results in 2-3 deaths per year from this cause.

Introduction to Altitude Illness

Human bodies have built-in adjustment mechanisms that can optimize performance at higher altitudes. This process is known as acclimatization. The power of acclimatization can be demonstrated by the following example. If a person were transported suddenly to the summit of Mt. Everest (29,128 feet; 8848 meters), the person would lose consciousness in a few minutes, and most likely die within an hour or two due to acute hypoxia. However, over 60 people have climbed to the summit of Mt. Everest without using supplemental oxygen after acclimatizing for many weeks. This fact demonstrates how profound the process of acclimatization can be.

The process of acclimatization is still poorly understood medically. Traditionally, researchers focused on the increase in erythropoietin, and the gradual increase in red blood cells as being crucial. However, it now recognized that this process plays only a small role, and that increases in respiration (minute ventilation), and other more subtle adaptations at the hormonal and cellular level may be more important. If a person ascends slowly enough, these adaptive processes can take place effectively, and no illness will occur. If the person ascends more rapidly than the body can adjust, however, symptoms occur that are referred to as altitude illness.

altitude couple

Altitude illness is generally divided into three syndromes:

  • Acute mountain sickness (AMS),
  • High altitude pulmonary edema (HAPE),
  • High altitude cerebral edema (HACE).

Why cerebral symptoms predominate in some people and pulmonary symptoms predominate in others is not known.

AMS presents as headache, anorexia, and fatigue. The headache can progress from mild to excruciating, and lack of appetite can lead to nausea and vomiting. At some point, when the symptoms are severe enough, the syndrome becomes known as high altitude cerebral edema (HACE).

HACE is usually made when there are changes in consciousness and/or the presence of significant unsteadiness (ataxia) as elicited by the tandem gait test. HACE can progress rapidly to coma and death. HACE can present alone, or in combination with HAPE.

HAPE can present with or without cerebral symptoms. Symptoms are: ----Decreased exercise tolerance—increased difficulty walking up hill—to severe Breathlessness with exertion, l Chest fullness, Breathlessness at rest that can lead to the rapid development of pulmonary edema (fluid on the lung).

Some people at altitude develop peripheral swelling, affecting the face, hands, and feet. Although harmless by itself, it does mean that the person is not acclimatizing well, and can lead to other symptoms of altitude illness. As the person with peripheral swelling acclimatizes, they start to urinate frequently and symptoms improve.

Normal Adaptation to Altitude:

Acclimatization seems to be under genetic control. Some people adjust very easily to high altitude, and others cannot get above relatively moderate heights of 10,000 feet. The ease with which someone can acclimatize is fairly consistent from trip to trip. Currently, no reliable screening methods exist to determine who will be a good acclimatizer or not. Taking a past history in regard to previous trips to altitude is generally a good indicator, if the exposures are comparable. For example, someone who can ski successfully during the day at altitudes up to 10,000 feet, will not necessary do well if he or she flies to 10,000 feet and spends the night. However, someone who has flown into 10,000 feet in the past and done well, will likely do well the next time. Someone who flew into 10,000 feet and woke up with a headache the next day will probably have the same result the next time, and may be a candidate for Diamox (acetazolamide) prophylaxis. Both acclimatization and the onset of altitude illness take time, generally from 6-48 hours to occur. So, visiting a high altitude for a few hours will not necessarily predict what will happen once one spends the night at that altitude.

Virtually all people who sleep above 10,000 feet have an alteration in the control of their breathing during sleep. The result is a form of abnormal breathing in which increasingly deep breaths are followed by a brief (5-30 seconds) period of breath holding (apnea). The person may awaken suddenly with a profound sense of shortness of breath . Periodic breathing at altitude responds to acetazolamide 125mg taken before bed.

Altitude Advice for Travelers:

Travelers on prolonged trips to high altitude, such as trekkers in Nepal, Peru, or Tibet should be taught that sensible itineraries are only the first step in avoiding severe altitude illness. Most trekking itineraries are a middle-of-the-road approach, and do not guarantee that all clients will not get altitude illness. The main goal of altitude illness advice is not to avoid getting altitude symptoms at all, but to react appropriately if altitude symptoms do occur. In other words, it's okay to get altitude illness, but it's not okay to die from altitude illness.

The main safety points in regard to altitude illness can be summarized in the following three rules:


Three Rules to Avoid Dying of Altitude Illness

  • Learn the early symptoms of altitude illness and be willing to recognize when you have them.
  • Never ascend to sleep at a higher altitude with any symptoms of altitude illness.
  • Descend if your symptoms are getting worse while resting at the same altitude.

When we review cases of fatal altitude illness, we almost invariably find that the person ascended with symptoms that could have been recognized as due to altitude illness. In most of these cases, the symptoms were either ignored, minimized, or attributed to another cause. In organized trekking groups, there is a great deal of pressure to keep up with the group schedule or be left behind. Since leaving a client behind is problematic logistically for a trekking group, even the leader can contribute to the denial of altitude symptoms. Trekkers who are traveling with an organized trekking group may have a false sense of security in regard to their risk of dying from altitude illness.

A 1991 study showed that trekkers in organized trekking groups had a statistically significant increased risk of dying compared to trekkers who were not in an organized group.

This fact emphasizes that group pressure and the reluctance to be left behind if one admits symptoms is a risk factor for dying from altitude illness. Thus, being willing to recognize altitude symptoms when they are present is a key point.

AMS symptoms will invariably worsen with ascent. Occasionally, however, it is necessary to ascend in order to get to a lower altitude, such as crossing a pass. If the symptomatic person appears to have the ability to make it over the pass, and will sleep at a lower altitude that night, this is a risk that can be taken. But no one with any symptoms of altitude illness should ascend to sleep at a higher altitude.

Most symptoms of altitude illness occur after spending the night at a higher altitude. If the rate of ascent has been reasonable, these symptoms usually resolve with a day's rest at the same altitude. However, if the person's symptoms continue to worsen during the day, descent is mandatory. Usually this decision should be made by around 3:00 p.m. in a trekking setting so that descent can be made during daylight.

However, descent should never be delayed because it is "too late" in the day.

Symptoms can either begin while ascending to a new camp, or after spending the night at the new height. In general, symptoms that begin in the morning after spending the night at a new altitude are more likely to clear up with rest at the same altitude than symptoms that began the day before while ascending to the camp.

Differential Diagnosis of Altitude Illness

The diagnosis of altitude illness at altitude requires a high index of suspicion. Trekkers have been advised for years that: "If you are not doing well at altitude, it's altitude illness until proven otherwise." This is sound advice, and was formulated to assure that altitude illness is considered in the differential diagnosis of any illness at altitude. However, other illnesses can occur at altitude that mimic altitude sickness, but may have significantly different implications. The key to differentiating between altitude illness and other medical conditions at altitude is the history of the present illness and the presenting symptoms.

Headache, anorexia, nausea, vomiting, and profound fatigue can all be symptoms of AMS. Diarrhea is not associated with altitude illness. Fever can occur with HACE or HAPE, and can be a confusing finding.

The headache associated with AMS often starts at the back of the head and radiates forward, and is constant in nature. But a throbbing frontal headache can also be due to altitude. It is imperative that all headaches at altitude are treated as altitude headaches, and no further ascent is attempted until any headache has disappeared. The symptoms of altitude illness almost always have a gradual onset, and get worse slowly over several hours.

Loss of vision secondary to altitude is rare. Recently, reports have surfaced that people who have undergone corrective laser surgery have developed severe short-sightedness at altitude and become functionally blind. This condition reverses readily with descent, but could be a fatal obstacle for a high altitude mountaineer stranded blind on a Himalayan mountain ridge.

HAPE presents with unusual breathlessness upon exertion, and eventually at rest. Cough is usually present, but cough at high altitude is so common from other causes that it is rarely a useful clinical sign of HAPE. Descent is mandatory as soon as HAPE can be suspected, as the symptoms can progress rapidly, and death can occur within hours of recognizing clinical HAPE. Unfortunately, exertion considerably worsens HAPE.

In order for symptoms to be attributed to altitude illness, they must begin as the person is ascending. A person who has been asymptomatic at the high point of a trek cannot develop AMS while descending. Virtually all life-threatening altitude illness is due to ascending with recognizable symptoms.

Prevention and Treatment of Altitude Illness

Gingko Biloba

This natural product helps prevent AMS. Starting a week before ascent by taking 80-120mg twice a day will help prevent AMS. The mechanism is unknown by it may work on nitric oxide. It should not be used with blood thinners. One should buy a recognized brand.

Acetazolamide (Diamox ®)

Acetazolamide is the medication with the longest history of use for preventing and treating AMS. Initially it was given for three days before ascent, but it is now thought that starting the day before is adequate.

The recommended dose:

Prevention: 125 mg Twice a day. It should be started one day before crossing the 9,000 foot level and continued during ascent and for first 2 days at high altitude.

Treatment: 250mg Twice a day until symptoms improve. Pediatric dose: 5mg/kg/body weight in two divided doses.

Acetazolamide is a carbonic anhydrase inhibitor and its mechanism of action is thought to be to acidify the blood, causing an increase in respiration centrally and an increase in oxygenation . It works as a diuretic ( promotes urination), but this appears to be a side-effect at present, rather than a benefit. People taking acetazolamide invariably notice an increase in urination, and the presence of pins and needles sensation in their fingers and toes . Acetazolamide is distantly related to sulfa drugs, and people with a known sulfa allergy should not take acetazolamide. However, allergic reactions to acetazolamide are extremely rare. Acetazolamide is also a very effective tool for treating the periodic breathing and sleep apnea that occurs at altitude. Should be avoided in pregnancy and when breast feeding.

Pressurization and Oxygen

It was once written that altitude illness had three treatments: descent, descent, and descent. Descent remains the critical treatment of all altitude syndromes, but the availability of bottled oxygen, the invention of pressurization bags, and the recognition of the value of three medications—acetazolamide, nifedipine, and dexamethasone--have expanded the choices when confronted with altitude illness.

Descent invariably improves altitude illness. However, in severe cases, descent must continue either until clear signs of improvement are recognized, or the person is below the altitude at which his symptoms have started. As mentioned above, it is not necessary to descend until all symptoms are gone, as this can take up to 48-72 hours to take place. Any sign of improvement usually heralds the crossing of the acclimatization line, and further improvement can be expected.

Pressurization in a commercial pressurization bag effectively mimics descent. The first commercial pressurization bag was created by Igor Gamow in the late 1980's.

Approximately 24" by 80" in size, with an airtight zipper, the bags are inflated by a rafting foot pump. An automatic blow-off valve limits the inside pressure to 2 pounds per square inch, and the steady leaking of air through the valve requires continuous pumping, which assures a steady flow of fresh air inside (usually about 10-15 pumps per minute). The amount of descent achieved within the bag depends on the height at which the descent began, but the amount of descent is usually about 1/3 the current height (that is, the bag lowers someone from 14,000 to about 9000 feet). People generally tolerate being placed in the bag, but people with severe HAPE have difficulty lying flat, which is required in order to fit in the bag.

A treatment of one hour is usually enough to dramatically improve mild to moderate AMS. Relapse occasionally occurs, but often does not. In more severe cases, several hours in the bag may be necessary, and repeat treatments may also be necessary if symptoms relapse. However, treatment in the bag can effectively mimic descent, and a person can be maintained at altitude if descent is problematic due to darkness, cold, storm, or difficult terrain. Bottled oxygen is heavy to carry, and there is usually not enough oxygen available to use freely.

Dexamethasone (Decadron ®)

When HACE was thought to be due to diffuse hypoxic cerebral edema, dexamethasone was often tried to treat severely ill patients. The effects of treatment on comatose patients was not very dramatic, and dexamethasone did not appear to have a very strong role to play in the treatment of altitude illness. Then, a pressure chamber study demonstrated that dexamethasone given prophylactically was effective at preventing AMS. This led to field studies that demonstrated that dexamethasone was also effective at treating mild to moderate AMS, and even improving HACE prior to the onset of coma.

Since then, people have used dexamethasone prophylactically and therapeutically in the field.

Prevention: Decadron: 2mg every 6 hours or 4 mg every 12 hours


  • AMS: 4mg every 6 hours by mouth or by injection.
  • HACE: Initial dose of 8 mg followed by 4mg every 6 hours by mouth or injection

Mechanism of action unknown. Can be life saving in severe cases and when descent not immediately possible.

Currently, it is felt that dexamethasone can be safely used to facilitate the evacuation of someone with relatively severe AMS or HACE. Once dexamethasone is given, the person should not move up to sleep at a higher elevation until dexamethasone has been discontinued for 24 hours or more.


Nifedipine is a calcium channel blocker that effectively lowers pressure in the pulmonary artery. Initial studies in Italy showed a dramatic improvement of HAPE in a group of people who get HAPE easily and volunteered to climb rapidly to over 15,000 feet. Nifedipine has been added to the list of drugs known to be effective in treating altitude illness. However it should not be relied upon to be life-saving, in the absence of other therapy.

Treatment:10mg initial dose followed by 20-80 mg of extended release formulation every 12 hours.

Other Treatments

  • Furosemide ( diuretic) in HAPE –
  • Viagra in HAPE ( reduces pulmonary vascular pressure).
  • Anti-vomiting medications.
  • Anti-inflammatory medications for headaches.

Effect of High Altitude on Pre-Existing Medical Conditions

Hematological System

Even moderate altitudes, such as those encountered in airplane travel, can trigger a sickle cell crisis in a person with sickle cell anemia. High altitude is clearly contraindicated in this population. People with low red cell counts could experience difficulty adjusting to high altitude, as their oxygen-carrying capacity would already be low. They would need to proceed with caution. Patients with polycythemia could experience problems at altitude with greater risk of blood clots and embolism.

Endocrine System

Stable diabetics can travel safely to high altitude if they are comfortable with self-monitoring and are willing to pay closer attention than usual to their glucose balance. High altitude can be associated with severe ketoacidosis for reasons that are not yet clear. However, Shlim reported 5 cases of ketoacidosis associated with high altitude (above 16,000 feet), and 3 of these people died.

Risk factors for developing ketoacidosis at altitude include associated illness (gastroenteritis, respiratory infection, and altitude illness), and the possible adverse interplay of respiratory alkalosis which could mask a deepening metabolic acidosis. Acetazolamide was used in at least two of these cases, and may have further blocked the body's attempt to correct the acidosis. A further practical problem for diabetics is the need to keep their insulin supplies at close hand and unfrozen during a long, cold backcountry journey.

Pregnancy and High Altitude Travel

When pregnant women inquire about the risks of altitude on the fetus, there is no data to turn to. However, pregnancy is an emotional issue, and the question needs to be carefully addressed. There are no reported cases of high altitude exerting a negative outcome on pregnancy in a trekker or climber.

Oxygen saturation is fairly well maintained up to an altitude of 10,000-12,000 feet. After that, the person approaches the steep portion of the oxy-hemoglobin dissociation curve, and blood oxygen levels drop precipitously. A well acclimatized person at 14,000 feet altitude has a pO2 of 55 mm hg. A pregnant woman who presented to an emergency room at sea level with a pO2 of 55 would be immediately placed on oxygen! Because of the rapid drop-off in oxygenation above 12,000 feet or so, we generally recommend that pregnant women avoid exposures above that height. However, there are numerous anecdotal stories of women who have traveled higher while pregnant and gave birth to normal children.

Practitioners who counsel pregnant women regarding high altitude exposure should take into account the following: the outcome of pregnancy is always somewhat uncertain. An adverse outcome could be due to any number of causes, but if the woman chooses to go to high altitude during the pregnancy, she may feel that the high altitude exposure was the cause. Therefore, the woman should carefully weigh the need to go on this particular high altitude trip at this time versus the potential for having regret should there be an adverse outcome of the pregnancy.

If the high altitude exposure is also coupled with traveling in a third world country, the woman should be further counseled regarding the risks of diarrhea and other infectious diseases, as well as the potential for trauma in third world conveyances. Remoteness from medical care could also be a problem if a miscarriage or early labor should occur.


Travelers planning to travel to high altitude can be re-assured that a slow itinerary and awareness of the symptoms of altitude illness can prevent any likelihood of dying of altitude illness. The acclimatization line concept is useful in presenting a more graphical illustration of planning itineraries and evaluating symptoms after they have occurred. Treatment options have expanded in recent years, but none of these options are superior to descent, which should always be the first choice in severe cases, if physically possible.

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