PREVENTION OF ALTITUDE-RELATED DISORDERS

Avoid direct or sudden ascent to a sleeping altitude above 9,020 ft (2,750 m). Acclimatization requires gradual exposure to altitude, with a rate of ascent not to exceed 1,500 ft (457 m) per day at altitudes above 8,000 ft (2,438 m). Rest days at a constant altitude are essential at heights above 10,000 ft (3,048 m). Acclimatization is achieved by adhering to a schedule of ascent:

In addition, the drug acetazolamide (Diamox) has proven to be useful in stimulating breathing, diminishing the sleep disorder associated with acute mountain sickness (AMS; see page 341), facilitating the body’s normal adjustment to high altitude, and thus improving nocturnal oxygenation. It is administered in a dose of 125 to 250 mg twice a day beginning 24 hours before ascent, and continued for a period of 2 days; within this period, the initial physiological acclimatization process should become operative. It may also be given as a 500 mg sustained-action capsule every 24 hours, with perhaps fewer side effects. Acetazolamide should be used if an ascent will be unavoidably rapid.

Children who have previously suffered from acute mountain sickness may benefit from acetazolamide, which should be administered in a dose of 5 mg/kg (2.2 lb) of body weight per day, in two divided doses, up to 125 mg per day. Diamox has a diuretic (increased urination) effect, so that it is extremely important to drink sufficient fluids to prevent dehydration. Fluid losses are generally greater at high altitude, so do not rely on thirst as a gauge of adequate fluid intake. Drink enough to keep the urine clear and light colored. Diamox is no substitute for proper acclimatization!

One study indicated that administration of inhaled salmeterol, a drug that affects transport of sodium and water in cells, may help decrease the risk of HAPE. The application of this finding to current recommendations for prevention and treatment is yet to be fully determined.

When you’re traveling at high altitudes, avoid the use of alcohol, stay warm, keep out of the wind, avoid exhaustion, and eat regularly to avoid weight loss. A diet relatively high in carbohydrates may be preferable to one high in fat and protein. Avoid the use of alcohol or any drugs for sleep during the first few days at altitude. Disturbed (poor quality, interrupted) sleep is common at high altitude. Acetazolamide, 125 mg by mouth at bedtime, diminishes the “periodic breathing” associated with sleep disturbance and therefore improves oxygenation, resulting in improved sleep quality. If insomnia is severe after the acclimatization process has occurred, zolpidem (Ambien) 5 to 10 mg, temazepam (Restoril) 10 to 15 mg, or zaleplon (Sonata) 5 to 10 mg by mouth may be used with caution under the guidance of personnel extremely experienced with high-altitude medical syndromes. A sleeping aid drug may be used in combination with acetazolamide.

It is not known if sleep apnea contributes to AMS or HAPE. However, a person with sleep apnea should be extremely cautious when traveling at high altitude. Findings suggestive of sleep apnea include the following: daytime—excessive sleepiness, feeling tired on awakening, fatigue, irritability, difficulty with simple tasks, and shortness of breath; nighttime—loud snoring, witnessed episodes of diminished or absent breathing, poor sleep, frequent awakening, frequent urination at night, and bedwetting.

Since oxygen is transported in red blood cells, it is advisable to avoid being anemic at high altitude. Iron-deficiency anemia is common in women, related to menstrual bleeding. If this is recognized, it should be corrected under the supervision of a physician with the administration of ferrous sulfate 300 mg per day; note that a side effect is constipation.

A pregnant woman who wishes to travel to high altitude should be certain that she has a normal pregnancy (e.g., normal blood pressure, no abnormal bleeding, placenta in proper position as determined by ultrasound if necessay). There is a possible increased risk for dangerous hypertension associated with pregnancy (preeclampsia) at high altitude. Proper acclimatization is essential. Try to keep the sleeping altitude no higher than 10,000 ft (3,048 m) and never above 12,000 ft (3,658 m).

In addition to the effects of less oxygen available at high altitude, mountaineers are subjected to other environmental hazards. Temperature decreases with altitude by an average of 11.7°F (6.5°C) per 3,280 ft (1,000 m). Ultraviolet light penetration increases approximately 4% to 6% per 984 ft (300 m) gain in altitude, which increases the risk for sunburn, skin cancer, and snowblindness. Sunlight reflecting off glaciers absent a cooling wind can transfer intense radiant heat. The dry air and rapid breathing predispose to dehydration.

Physical fitness, while desirable for mountaineering, does not protect against high-altitude illness. This cannot be overemphasized. It is, of course, good to be in excellent physical condition, but this does not substitute in any way for proper acclimatization.

In terms of preexisting conditions and the risk for high-altitude illness, here are some other general guidelines:

If a person suffers from any chronic condition, he should clear any travel of an extreme nature (high-altitude, cold, hot, exertion) with a physician and become educated on potential problems and solutions.

HIGH-ALTITUDE PULMONARY EDEMA

Pulmonary edema is excess fluid in the lungs, either in the lung tissue itself or in the space normally used for gas exchange (oxygen for carbon dioxide). Fluid in the lungs renders them unable to perform their normal task, and thus the victim cannot get enough oxygen.

High-altitude pulmonary edema (HAPE) usually occurs in an unacclimatized individual—typically a male—who rapidly ascends to an altitude that exceeds 8,000 ft (2,438 m), particularly if heavy exertion is involved. Prior traditional physical conditioning is not a factor; many cases involve young, previously healthy individuals. If the victim exercises above 8,000 ft (2,438 m) but sleeps at a lower altitude (such as 6,000 ft, or 1,829 m), his risk for developing HAPE is much less.

Symptoms begin 1 to 3 days after arrival at high altitude. They include shortness of breath, cough, weakness, easy fatigue (especially when walking uphill), and difficulty sleeping. Signs of acute mountain sickness (AMS; see page 341) are often present. As greater amounts of fluid accumulate in the lungs, the victim develops drowsiness, severe shortness of breath, and rapid heart rate; his initial dry and gentle (“soft”) cough produces white phlegm and then blood (pink, frothy sputum’a late sign); he exhibits confusion and cyanosis (bluish discoloration of the skin, particularly noticeable in the nail beds and lips). If you place an ear to the victim’s chest, you may hear crackling or gurgling noises. The symptoms worsen at night. Rapidly, the victim becomes extremely agitated, disoriented, and sweaty; he is in obvious extreme respiratory distress. Confusion, collapse, and coma follow. The victim may show a fever of up to 101.3°F (38.5°C).

As soon as the earliest signs of HAPE are present, the victim should be evacuated (carried, if necessary) to a lower altitude at which there were previously no symptoms. Such warning signs include rapid heart rate (greater than 90 to 100 beats per minute at rest), weakness, shortness of breath, cough, difficulty walking, inability to keep up, and poor judgment. Maximum rest is advised. The definitive treatments are descent and the administration of oxygen; if it is available, oxygen at a flow rate of 4 to 6 liters per minute should be administered by facemask (see page 431). Improvement is rarely noted until oxygen is administered or descent of at least 1,000 to 2,000 ft (304 to 608 m) is accomplished. If the victim improves, diminish the flow rate of oxygen to 2 to 4 liters per minute to conserve supplies.

In no case should a victim be left to descend by himself. Always have a healthy person accompany him. If the victim must be carried down, he should be kept in a sitting position, if possible. Keep him warm, as well.

Have the victim inhale albuterol or salmeterol from a metered dose inhaler according to the directions. The administration of fluid pills (diuretics) is controversial and should be done only under strict medical supervision, as should the administration of morphine.

Some aid stations in high-altitude regions are equipped with an inflatable pressure bag (such as a “Gamow bag”) large enough to enclose a human. This is used to simulate conditions at lower altitude and may be used to treat moderate or severe high-altitude illness. The cylinder-shaped Gamow container is a small, portable hyperbaric chamber that can be pressurized with a foot pump to 2 lb (0.9 kg) per square inch, which simulates a descent of approximately 5,248 ft (1,600 m); the exact equivalent of descent depends on the altitude at which the bag is deployed. The victim should be placed in the bag for a minimum of 2 hours. In addition, oxygen from a tank can be administered to the victim by facemask (see page 431) within the bag.

A drug that physicians are using successfully to treat HAPE is nifedipine, which lowers obstructive pressure in the pulmonary arterial circulation (which carries deoxygenated blood from the heart through the lungs). The first dose is 10 mg chewed, and then swallowed. This is followed by 10 mg every 4 to 6 hours, or 30 mg extended-release preparation (Adalat CC) every 12 to 24 hours. The dose in children for HAPE is 0.5 mg/kg (2.2. lb) of body weight (to a maximum dose of 10 mg) by mouth every 8 hours. Since this drug is also used to treat high blood pressure, a side effect can be low blood pressure and dizziness, particularly if the victim is dehydrated. These particular side effects seem to be minimal when the extended-release preparation is used. Nifedipine has also been used successfully to prevent HAPE in subjects with a history of repeated episodes, but is not yet recommended for prevention in the general population. The dose for prevention is 20 to 30 mg of the extended-release preparation every 12 hours. Other drugs that have been suggested for prevention include acetazolamide 125 to 250 mg twice a day (or 500 mg sustained release once a day), inhaled salmeterol 2 puffs every 8 to 12 hours, tadalafil 10 mg every 12 to 24 hours, sildenafil 30 mg three times a day, and dexamethasone 8 mg every 12 hours beginning 2 days before high-altitude exposure.

Sildenafil (Viagra) 50 mg by mouth every 8 hours has been used to treat HAPE, because of its effect on lowering pressure in part of the circulation within the lungs.

Once a victim has been judged to suffer from any degree of HAPE, he should no longer be a candidate for high-altitude travel until cleared by a physician. Such a precaution does not include routine jet airplane transportation.

HIGH-ALTITUDE CEREBRAL EDEMA

High-altitude cerebral edema (HACE) is the medical term for a disorder (theoretically linked to brain swelling) that involves an alteration of mental status seen at high altitude, related to diminished atmospheric oxygen. It may be present in someone who has worsened from acute mountain sickness (see below) or who is suffering from HAPE. Symptoms include headache (often throbbing), difficulty walking (loss of balance, inability to walk a straight line, staggering, or frank inability to walk), clumsiness, confusion, amnesia, difficulty in speaking, drowsiness, vomiting, and, in severe cases, blurred vision, blindness, unconsciousness, paralysis, and/or coma. Other symptoms may include mood changes, hallucinations, paralysis of an arm and/or leg, and seizures (rare). Victims are often gray or pale in appearance. Imbalance or the inability to walk heel to toe in a straight line is a very worrisome sign and should prompt immediate action to treat the victim. An exremely drowsy person may slip rapidly into a coma. “High-altitude headache” is often the first noxious symptom noted on exposure to high altitude, and may be the harbinger of acute mountain sickness (AMS—see below).

The treatment for HACE is immediate descent to an altitude below one at which the victim previously had no symptoms, and the administration of oxygen at a flow rate of 5 to 10 liters per minute by face mask or nasal cannula (tube) (see page 431). If the victim becomes severely ill, he should be brought (carried, if necessary, and preferably in the sitting position) to a lower altitude (below 5,000 ft, or 1,524 m). In addition, administration of the steroid drug dexamethasone (Decadron) 8 mg first dose, and then 4 mg every 6 hours until descent is accomplished, may be helpful. The pediatric dose of Decadron is 0.5 mg/kg (2.2 lb) of body weight for the first dose, followed by 0.15 mg/kg every 6 hours. Again, never leave a potentially seriously ill person to fend for himself. A victim of HACE or HAPE can deteriorate rapidly, and most will need to be transported down the mountain. As with HAPE, a Gamow bag can be used for treatment. Because the early symptoms of acute mountain sickness (see below) and HACE are similar, pay close attention to the condition of ill members of your climbing party.

ACUTE MOUNTAIN SICKNESS

Acute mountain sickness (AMS) is the most common altitude-related disorder. It affects those who ascend to altitudes above 8,200 ft (2,500 m) from below 4,921 ft (1,500 m) and are unable to keep pace with acclimatization. A person who is partially acclimatized may be stricken if he ascends rapidly to a higher altitude, overexerts, or uses sleep medication (which can be a respiratory depressant). Symptoms, which may be quite subtle in the beginning, are most commonly headache (in its mildest form sometimes called “high-altitude headache”), followed in incidence by fatigue, dizziness, and loss of appetite. Other symptoms include insomnia, nausea, vomiting, drowsiness, weakness, and apathy. Some people have described the suffering associated with AMS as similar to a hangover. Children are prone to nausea and vomiting as a manifestation of AMS. The lips and fingernails may have a blue discoloration (cyanosis) if HAPE is present.

The most common and disabling symptom of AMS is headache that typically occurs on the second or third day at high altitude and may be complicated by difficulty in walking (particularly if HAPE is present) and impaired memory. The headache is mild to severe, throbbing, in both temples or the back of the head, worse during the night and on awakening, and worsened by straining or bending over. Mild symptoms of HACE accompany AMS; they include decreased appetite, mood swings, and lack of interest in activity. Some victims complain of a deep inner chill. AMS is sometimes mistaken for a viral illness, such as the flu, or exhaustion or dehydration. Lassitude may be so severe that the victim is too apathetic to contribute to his or her own basic needs. The symptoms of AMS may be confused with dehydration, exhaustion, bacterial or viral infection, hypothermia, carbon monoxide poisoning, migraine headache, low blood sugar, transient ischemic attack or stroke, illicit drug ingestion, or psychiatric disease.

One hallmark of AMS, known as periodic breathing, is an alteration of the normal sleeping pattern. Sleep is fitful, with periods of wakefulness or disturbing dreams. The pattern of breathing becomes irregular, such that the sleeper has periods of rapid breathing (very deep breaths) alternated with periods of no breathing. The latter can be quite startling to the casual observer—intervals of 10 seconds may pass without a breath. Acetazolamide, 62.5 to 125 mg at bedtime, diminishes periodic breathing, improves oxygenation, and is safe to use as a sleeping aid. Insomnia from other causes may respond to short-acting drugs for sleep, such as zolpidem (Ambien) 5 to 10 mg, zaleplon (Sonata) 5 to 10 mg, triazolam (Halcion) 0.125 mg, or temazepam (Restoril) 10 to 15 mg, but as mentioned previously, these medications must be used with extreme caution in a person who is suffering incipient AMS, because any amount of respiratory depression might lead to decreased oxygenation. Also, sleep medication may mask the symptoms of HACE.

Treatment for AMS includes rest, adequate fluid intake to avoid dehydration, and mild pain medicine for the headache. Oxygen administration (0.5 to 1.5 liters per minute by nasal cannula or simple open facemask) may be effective for the headache, as might be acetaminophen or a nonsteroidal antiinflammatory medication, such as ibuprofen. The victim may be led to a lower altitude, preferably at least 1,640 to 3,281 ft (500 to 1,000 m) below that where symptoms began. However, many victims of AMS will adjust to the current altitude in a period from 12 hours to 3 to 4 days, and therefore may remain at a stable altitude if symptoms are mild. In no case should a person attempt to climb to (or, particularly, sleep at) a higher altitude until the symptoms of AMS have completely subsided. If symptoms worsen appreciably while a person remains at rest at a constant altitude, descent is indicated. With mild AMS, acetazolamide (Diamox) can be administered in a dose of 250 mg by mouth every 12 hours until symptoms diminish. The dose in children is 5 mg/kg (2.2 lb) of body weight per day, in two divided doses, up to 250 mg per day.

Prochlorperazine (Compazine) 10 mg by mouth or 25 mg by suppository can be given for nausea and vomiting, with the added benefit that it may stimulate the beneficial ventilatory (breathing) response that is triggered by a low oxygen content in the blood (associated with altitude and called the “hypoxic ventilatory response”). The dose in children older than 2 years of age is 0.4 mg/kg (2.2 lb) of body weight per day, by mouth or by oral suppository, in three or four divided doses. Promethazine (Phenergan) is fine as an alternative for adults, in a dose of 25 to 50 mg by mouth or suppository. Aspirin, acetaminophen, or ibuprofen may be given for headache. Avoid the use of alcohol or other respiratory depressants.

If an oxygen cylinder is available (see page 431), low-flow (0.5 to 1.5 liters per minute) oxygen by nasal cannula (tube) or facemask is particularly effective if used for sleep. This alone may be adequate to halt the progression of mild AMS and allow a victim to acclimatize without descent to a lower altitude. However, if this approach is taken, the victim should not be left alone until all symptoms of AMS have resolved. The victim who spends a few hours in a hyperbaric chamber, which simulates descent, will notice diminution of symptoms and benefit from hastened acclimatization. The “Gamow bag,” and other similar lightweight fabric pressure bags, are inflated by manual air pumps. Inflation at 2 pounds per square inch is roughly equivalent to a descent of 5,249 ft (1,600 m). A few hours of pressurization may have noticeable beneficial effect for many hours. To completely eliminate AMS, it is sometimes necessary to remain within the bag for 12 hours or more.

If AMS is moderate to severe and certainly if there is reason to suspect that HACE is developing (the victim wishes to be left alone or is becoming confused, cannot perform simple tasks such as eating and dressing, is vomiting, and cannot walk a straight line), administer dexamethasone as previously recommended for HACE. AMS can progress to HACE with coma in 24 hours.

Dexamethasone is used by some climbers to prevent AMS. Dexamethasone should not be used for routine prevention, because it does not enhance acclimatization, but rather masks symptoms. It may be useful for persons who are performing a rapid ascent and who cannot tolerate acetazolamide, but with extreme caution, as it does nothing to prevent HAPE and if descent is delayed and dexamethasone discontinued, the rebound effect can cause rapid onset of severe AMS or HACE. It may be used to treat AMS in a dose of 4 mg by mouth every 6 hours. It should be used for no more than 48 hours, during which time descent should be undertaken, from where acclimatization may proceed.

Ginkgo biloba administered in a dose of 80 to 100 mg by mouth twice a day has been recently suggested to reduce the incidence of AMS, and perhaps to be helpful as a therapy. Caution is advised in choosing a natural product that has a validated amount of active ingredient(s).

If symptoms of AMS worsen despite 24 hours of additional acclimatization and/or treatment, have the victim descend immediately to a lower altitude. A reasonable descent is a minimum of 2,500 to 3,000 ft (762 to 914 m).

OTHER DISORDERS OF HIGH ALTITUDE