High altitude illness: avoiding the perils of the peaks.

While in the picturesque southwestern Colorado mountain town of Durango (elev. >6500 feet) I picked up a local climbing newsletter, which advised on its cover: "When in doubt, go higher." Great advice for seasoned climbers, I thought, but not meant for the altitude-newbie. Living in a state where the average elevation is 6800 feet above sea level, we in Colorado often overlook or minimize the hazards of venturing to high places. Vacation destinations for skiing, hiking, trekking, or camping in the Alps, Himalayas, Andes and Rockies are becoming more popular. Often we are asked to advise our friends or colleagues about health-related issues during these trips. Rapid ascents can be hazardous.

What is Mountain Sickness? Who is at Risk?

Mountain sickness or high-altitude illnesses are names for cerebral and respiratory problems that occur shortly after ascent to high altitude. The terms acute mountain sickness and high altitude cerebral edema refer to brain abnormalities. High altitude pulmonary edema may occur in conjunction with or without accompanying cerebral changes. Altitude illnesses can range in severity from mild to fatal.

At the root of the problem is hypoxia. The absolute percentage of oxygen in the air is the same, regardless of altitude; however, as altitude increases, the number of molecules in any given volume of air decreases. This makes less oxygen available to diffuse across the alveolar membranes into the red cells' hemoglobin. In a person at sea level, the arterial oxygen partial pressure is 90-95 mmHg; oxygen saturation is 97%. If that same individual travels to an altitude of 14,000 feet, the figures fall to 45 mmHg and 71% prior to acclimatization. With the increased tissue oxygen demands of exercise, blood oxygen saturation is accordingly lower.

As plasma and tissue hypoxia occur, the body reflexively begins to compensate. Minute ventilation increases, as does respiratory rate. Blood flow to the lungs also increases. In both the brain and lungs there is over perfusion of the microvasculature. Vessels then become leaky and fluid is exuded into the surrounding tissue spaces leading to edema.

Whether high altitude symptoms occur is determined by several factors. The rate of climbing is important--climbing faster is higher risk. The altitude reached and the altitude at which the person resides as well as individual physiology all play a role.

Travel from sea level to 5-6000 feet elevation can cause symptoms in some people. In Summit County, Colorado, there are a number of vacation destinations including Vail, Keystone, Copper, and Breckenridge mountains. Mountain sickness occurs in 22% of visitors to 7000-9000 feet altitude. The incidence rises to 42% of those who travel to 10,000 feet. If you live at an altitude below 900 meters (2950 feet) you are at high risk.

If you have suffered a bout of mountain sickness in the past, this places you in a higher risk category as well. Age is in one's favor: if you are over 50 years old, the risk of altitude sickness is lower. Women are less susceptible to high altitude pulmonary symptoms but equally susceptible to acute cerebral problems. Physical fitness and conditioning is not protective. Common conditions such as hypertension, coronary artery disease, diabetes and pregnancy do not affect susceptibility to altitude illness. Anemia, particularly sickle cell disease, creates a much higher risk.

How Do You Recognize Altitude Illness?

Acute mountain sickness generally begins between 12 and 24 hours after reaching altitude. It consists of headache and at least one of the following: 1) Intestinal symptoms such as nausea, vomiting, or loss of appetite, 2) dizziness or lightheadedness, 3) fatigue or generalized weakness and 4) insomnia or difficulty sleeping. The headache may vary in intensity from minor to incapacitating. It generally peaks upon awakening and abates somewhat after getting out of bed and moving around.

High altitude cerebral edema (HACE) is an advanced and potentially fatal form of mountain sickness. Brain edema leads to change in mental status, stupor or lethargy, ataxia or loss of balance, and eventually coma. Seizures are very rare.

High altitude pulmonary edema (HAPE) usually strikes the second night at a new altitude and is exacerbated by exercise and cold temperature. Chest tightness, shortness of breath, weakness with decreased exercise performance, cough and tachycardia are seen. Fever is common. Wheezing, congestion and cyanosis are also seen. Many people who have HAPE also have acute mountain sickness or HACE.

Additional symptoms that may indicate altitude illness include vertigo, "feeling hung over," thirst, tinnitus (ringing in the ears), nightmares and change in vision with retinal hemorrhage, slowing of speech, excess flatulence, swelling of the hands and feet, and transient global amnesia.

Beware: people who are affected may not realize that there is a problem. It pays to be alert to potential danger signs in your companions. Look out for complaints of headache, skipping meals, acting in an antisocial manner, frequent stumbling or losing footing, refusal to drink and an inability to function as a group or team member. Adventure racers have been pulled from the course due to these symptoms which can impede race performance as well as team safety.

Beware as well that other conditions can mimic acute mountain sickness. These include hypothermia, dehydration, asthma, pneumonia, heart attack, hypoglycemia and exhaustion. The onset of symptoms more than three days after arrival at altitude, absence of headache and a rapid response to fluids or rest suggest another diagnosis.

What is the Remedy?

First and foremost: Avoid going any higher! Further ascent should be delayed until all symptoms have resolved, because the oxygen level will only worsen. If stopping does not help, or if there are signs of cerebral or pulmonary edema, you must immediately descend to a lower altitude. Fortunately, a descent of only 500-1000 meters (1600-3300 feet) usually leads to resolution of the illness. Simulated descent with a portable hyperbaric chamber, now commonly used in remote locations, is also effective. Supplemental oxygen is also a treatment of choice. For mild headache alone, a single dose of ibuprofen or acetaminophen has been shown to ameliorate or resolve the pain.

Acetazolamide (Diamox) acts to facilitate renal bicarbonate excretion. This changes the body's acid-base balance and promotes ventilation by increasing the depth of breathing. It also acts as a diuretic to improve fluid overload. Dexamethasone (Decadron) is a corticosteroid, which reduces brain swelling and also improves lung function. Both medications work within 12-24 hours.

Prevention Strategies

The best way to avoid altitude illness is to try to move to high altitudes gradually, giving the body time to adjust and adapt to the lower oxygen levels. This is more critical for people who live at sea level. If you are going above 8000 feet, you should not climb more than 1000 feet per day if you suspect you are developing altitude-related symptoms. In one study, ascending to an altitude of 11,500 feet over four days reduced the incidence and severity of acute mountain sickness by 41% compared with rapid ascent.

Most experts recommend prophylaxis with medications for travelers who plan an ascent from sea level to over 3000 meters (9840 feet) in one day and for those with a history of acute mountain sickness. Both Acetazolamide and/or Dexamethasone starting 12-24 hours before high altitude exposure and continued three to four days prevent sickness.

For people who have had high altitude pulmonary edema, the calcium channel blocker nifedipine (procardia) can be helpful. Interestingly, there are two studies showing that the herb Ginkgo biloba prevented acute mountain sickness. Prophylactic aspirin (one tablet every four hours for three doses) prevented headache. There is no evidence that water intake, preventing dehydration, or attaining a state of over-hydration combats or prevents high altitude sickness!

When planning your high altitude adventure remember to stay in touch with your body and your fellow trekkers! It is tempting to continue exercise assuming that you are simply tired, dehydrated, have low blood sugar, or a low core temperature. Do not make the mistake of treating altitude sickness by drinking water, eating, or putting on more clothing. The mountain adventurer who misunderstands or mistreats altitude sickness and continues to climb could be risking serious or life-threatening consequences. Be safe, be prepared, and when in doubt, do not climb higher!

REFERENCES

Cymerman A, et al. Speech Motor Control and Acute Mountain Sickness: Avat. Space Environ Med. 2002;73(8):766-72

Pray WS. Preventing Acute Mountain Sickness. US Pharmacist. 2001; 26(3).

Procelli MJ, et al. A Trek to the Top: A review of acute mountain Sickness. J AM Osteopathic Assoc. 1995;12:718-20.

Coote JH. Medicine and Mechanisms in Altitude Sickness. Sports Med. 1995;4(20):148-59.

Roach RC, et al. Exercise Exacerbates Acute Mountain Sickness at Simulated High Altitude. J Appl Physiol. 2000;88(2):581-5.

Schneider et al. Acute Mountain Sickness: Influence of Susceptibility, Preexposure, and Ascent Rate. Med Science in Sports and Exercise. 2002;3:1886-91.

Talbot TS. To Air is Human: Altitude Illness During an Expedition Length Adventure Race. Wilderness Environ Med. 2004;15(2):90-94.

Litch. High-Altitude Global Amnesia. Wilderness Environ Med. 2000;11(1):25-8.

Vasankari et al. The Effect of Endurance Exercise at Moderate Altitude on Serum Lipid Peroxidation and Antioxidative Functions in Humans. Eur J Appl Physiol. 1997;75:396-9.

Francene Mason is the Medical Director of HealthLinks Clinic in Boulder, Colorado, as well as an American Running Association Clinic Advisor and co-author of The FORCE Program: The Proven Way to Fight Cancer Through Movement and Exercise. Questions or feedback for the author may be directed to [e-mail]

by Francene Mason, MD