High Altitude Medical Advice for Travelers

• Types of High Altitude Travel
• Epidemiology of Altitude Illness
• Introduction to Altitude Illness
• Normal Adaptation to Altitude
• A Brief Review of the Pathophysiology of altitude Illness
• Acclimatization Advice and Schedules: The Acclimatization Line
• Altitude Advice for Travelers
• Three Rules to Avoid Dying of Altitude Illness
• Differential Diagnosis of Altitude Illness
• Treatment of Altitude Illness
• Effect of High Altitude on Pre-Existing Medical Conditions
• Summary

Travel medicine practitioners frequently see people before they travel to high altitude destinations. Many of these clients are concerned about how they will react to high altitude, and wish to be provided with guidelines for planning a safe trip. Travelers occasionally return from a high altitude trip with persistent symptoms, or having had an illness associated with altitude. The purpose of this review is to provide guidelines that will hopefully simplify the giving of prophylactic advice to high altitude travelers, to review the differential diagnosis of illness at altitude, and to help with pre-travel decisions in people who are concerned about the effects of altitude on pre-existing conditions.

Types of High Altitude Travel

People can be exposed to high altitude in different ways. One can travel to a resort town in the mountains that may be located at an altitude ranging from 4,000 feet to 10,000 feet. Activities during the day—skiing, hiking, or sightseeing—may take the person higher, but sleeping will generally be at the same altitude. 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 Himalaya 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

Travel to resorts in mountain areas puts millions of people at risk from mountain sickness symptoms. In the past, these symptoms were often erroneously attributed to the flu or alcohol hangovers. Deaths have occurred at ski resorts in the United States. 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 Kathmandu, one gets to a higher altitude even more quickly than flying. Thus, a percentage of people are certain to get altitude illness symptoms on these itineraries. Prophylactic medication may be indicated when the itinerary unavoidably violates altitude sickness prevention guidelines.

Trekking in the Himalaya 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. Trekking agencies feel pressure to offer shorter trips for busy people who have difficulty taking 3-4 weeks holiday at one time. 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 erythropoetin, 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 illness is generally divided into three syndromes: acute mountain sickness (AMS), high altitude pulmonary edema (HAPE), and high altitude cerebral edema (HACE). These syndromes are believed to be connected pathophysiologically, but just why cerebral symptoms predominate in some people and pulmonary symptoms predominate in others is not known.

The cerebral form of altitude illness begins as acute mountain sickness. AMS presents as headache, anorexia, and fatigue. The headache can progress from mild to excruciating, and anorexia can lead to nausea and vomiting. The fatigue can progress to extreme lassitude. At some point, when the symptoms are severe enough, the syndrome becomes known as high altitude cerebral edema. The diagnosis of HACE is usually made when there are changes in consciousness and/or the presence of truncal 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. If pulmonary symptoms do occur alone, the progression is from decreased exercise tolerance—increased difficulty walking up hill—to severe breathlessness with exertion, substernal chest fullness, and ultimately breathlessness at rest. Breathlessness at rest can lead to the rapid development of fulminant pulmonary edema. The production of pink, frothy sputum is a pre-terminal event.

Some people at altitude develop peripheral edema, 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 edema acclimatizes, they often experience a profound diuresis and relief of symptoms. One can ascend with peripheral edema, but one needs to be extra cautious about the development of other symptoms.

High altitude retinopathy refers to the development of retinal hemorrhages while staying at high altitude. Usually only discovered when searched for by trained doctors, the hemorrhages have rarely occurred near the macula and presented with a visual field deficit.

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 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 periodic breathing in which increasingly deep breaths are followed by a brief (5-30 seconds) period of apnea. The cycle then repeats itself. If the apneic episode is prolonged, the person may awaken suddenly with a profound sense of dyspnea. Awakening suddenly in a tent at high altitude feeling that one can’t breathe can be a frightening experience, and is often mistaken for the onset of high altitude pulmonary edema. The immediate improvement upon awakening is usually sufficient proof that pulmonary edema is not present. Nocturnal awakening with dyspnea has triggered panic attacks in several individuals in Nepal. If periodic breathing at altitude is disturbing to the trekker, acetazolamide 125mg taken before bed can virtually eliminate the problem.