High altitude–related problems

Prevention of high altitude–related disorders

Avoid direct or sudden ascent to a sleeping altitude above 9000 ft (2743 m). If you travel from sea level to 8000 ft (2438 m) in one day, rest there for a day or two before going higher. Acclimatization requires gradual exposure to high altitude, with a rate of ascent not to exceed 1500 ft (457 m) per day at altitudes above 9000 ft (2743 m). Rest days at a constant altitude are essential at heights above 10,000 ft (3048 m). Add an extra night of acclimatization for every 1969 to 2953 ft (600 to 900 m) of ascent. For acclimatization purposes, mild exercise is fine, but extreme exercise might be deleterious. Make day trips to a higher altitude with a return to a lower (proper for acclimatization) altitude for sleep. Acclimatization is achieved by adhering to a schedule of ascent:

• For any climb above 9843 ft (3000 m), spend an initial 2 to 3 nights at 8202 to 9843 ft (2500 to 3000 m) before proceeding higher. The first day should be a rest day. Don’t sleep at an altitude more than 984 ft (300 m) above the previous night’s sleeping altitude. If anyone shows signs of high altitude–related illness, spend additional time at this altitude. Don’t ascend to sleep at a higher altitude if you have any symptoms of high-altitude illness.

• For any climb above 13,000 ft (3962 m), all members of the party should add 2 to 4 days for acclimatization at 10,000 to 12,000 ft (3048 to 3658 m). Subsequent climbing should not exceed 1500 ft (457 m) per day. A rest day every 2 to 3 days is advised, along with an extra night for acclimatization with any ascent of 2000 ft (609 m) or more. The party should sleep at the lowest altitude that does not interfere with the purpose of the expedition and should sleep no higher than 1312 to 1968 ft (400 to 600 m) above the sleeping altitude of the previous night. The mantra is “Climb high—sleep low.” After a person has acclimatized by adhering to a schedule of slow ascent, it’s important to remember that even a few days at low altitude might cause the adjustments to disappear, so that a person is once again susceptible to high-altitude illness, particularly high-altitude pulmonary edema (HAPE).

The drug acetazolamide (Diamox) has proved to be useful in stimulating breathing, diminishing the sleep disorder associated with acute mountain sickness (AMS; see page 351), facilitating the body’s normal adjustment to high altitude, and thus improving nocturnal oxygenation and preventing AMS. It is administered in an adult dose of 125 mg twice a day (pediatric dose 2.5 mg per kg [2.2 lb] of body weight to a maximum dose of 125 mg) beginning 24 hours before ascent and continued for a period of 2 days after the highest altitude to be attained; within this period, the initial physiologic acclimatization process should become operative. It can also be given as a 500-mg sustained-action capsule every 24 hours. Acetazolamide should be used if an ascent will be unavoidably rapid. Don’t use acetazolamide in persons with a history of a severe allergic reaction (including anaphylaxis—see page 78) to sulfa or penicillin-derivative drugs. If you intend to use acetazolamide, take a trial dose of the medication at sea level well in advance of the high-altitude travel, to identify any adverse side effects. Be aware that acetazolamide commonly causes increased urination, altered (bitter) taste of carbonated beverages, numbness and tingling of hands and feet (particularly in cold weather or accompanying sudden temperature changes, such as washing in hot water), and sometimes bone marrow suppression or even impotence. The “usual” allergic reaction is a rash beginning a few days after starting the drug. Acetazolamide can also cause skin rashes (photosensitivity) upon sun exposure.

Ibuprofen has recently been shown to be somewhat effective in reducing the incidence of AMS. It was given to adults in a dose of 600 mg by mouth every 8 hours, beginning 6 hours before ascent. It has not yet been determined for how long after the maximum altitude is attained that the drug should be continued in order to maintain its beneficial effect. Furthermore, ibuprofen is a painkiller in and of itself, so if using it “masks” the hallmark headache symptom of AMS, which might be dangerous. Furthermore, there is a realistic concern that it might cause or worsen gastrointestinal bleeding at high altitude. Until more is known, if ibuprofen is used to prevent AMS, pay particularly close attention to the users.

Acetazolamide has a diuretic (increased urination) effect, so that it’s extremely important to drink sufficient fluids to prevent dehydration. Begin administering acetazolamide a day before ascent in order to get past the diuretic (excessive urination) effect, which is maximal in the first 24 hours. Fluid losses are generally greater at high altitude, so don’t rely on thirst as a gauge of adequate fluid intake. Drink enough to keep the urine clear and light colored. Acetazolamide is no substitute for proper acclimatization!

Using dexamethasone (Decadron), a steroid medication, to prevent AMS (and presumably, high-altitude cerebral edema [HACE; see page 352]), is controversial in the wilderness medicine community. Proponents note that it is very effective; opponents argue that it encourages too-rapid ascents and removes a “rescue drug” that should be reserved for treatment and not used for prevention. If it is used to prevent AMS (such as for persons who are allergic to acetazolamide and who must make a rapid ascent), it can be administered to adults in a dose of 2 mg by mouth every 6 hours or 4 mg by mouth every 12 hours, beginning 24 hours before ascent and optimally continued for no more than 48 hours, at which time the recipient should return to an altitude at or below the origin of the ascent. It is not recommended for use in children as a preventive drug.

Other substances have been advocated for prevention of high-altitude illnesses. These include drugs to prevent HAPE (see later for these recommendations), Gingko biloba (inconsistent results, perhaps related to purity of the compound and/or dose), antioxidant “cocktails” (not yet proved effective), and other medications such as naproxen, acetaminophen, antacids, and diuretics (none yet proved effective). Gingko biloba seems harmless but is not a substitute for acetazolamide. While adequate hydration is important, overhydration has never been shown to be of benefit to prevent or treat high-altitude illness. Chewed coca leaves, coca tea, and other coca-derived products should not be substituted for proven prevention methods.

“Pre-acclimatization” refers to a method where one attempts to mimic high altitude using a hypobaric (low ambient oxygen content) chamber, with or without exercise. It takes about 7 hours per day for a week at a simulated altitude of 2500 m, or not more than 2000 m below the target altitude of travel, to achieve acclimatization by this method. Wearing suffocating masks and exercising at sea level in the absence of low ambient oxygen does not achieve pre-acclimatization.

When you’re traveling at high altitudes, avoid the use of alcohol, stay hydrated and warm, keep out of the wind, avoid exhaustion, and eat regularly to avoid weight loss. Bring tasty foods so that you ingest sufficient calories. A diet relatively high in carbohydrates might 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 high altitude. Disturbed (poor quality, interrupted) sleep is common at high altitude. Acetazolamide 62.5 to 125 mg by mouth at bedtime diminishes the “periodic breathing” that has traditionally been associated with sleep disturbance, but it might be the enhancement of oxygenation and acclimatization achieved by taking acetazolamide that improve sleep quality. If insomnia is severe after the acclimatization process has occurred, zolpidem (Ambien) 5 mg, temazepam (Restoril) 10 to 15 mg, or zaleplon (Sonata) 5 to 10 mg by mouth can be used with caution under the guidance of personnel extremely experienced with high-altitude medical syndromes. Impaired performance (e.g., driving), behavior without conscious thought or intentions, or confusion might be present the morning after using zolpidem, particularly extended-release forms of the medication. A sleeping aid drug can be used in combination with acetazolamide.

It is not known if obstructive sleep apnea contributes to AMS or HAPE. However, a person with sleep apnea should be extremely cautious when traveling at high altitude. Sleep apnea is a condition of episodes that occur during sleep where a person’s upper airway collapses and becomes obstructed, accompanied by reduction or stoppage of breathing, all of which leads to low oxygen and high carbon dioxide levels in the blood and often awakening from sleep. An important risk factor for obstructive sleep apnea is obesity. 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. Acetazolamide used in combination with an auto-adjusted continuous positive airway pressure (auto-CPAP) device might be more effective than auto-CPAP alone in reducing breathing disturbances in persons with obstructive sleep apnea.

Since oxygen is transported in red blood cells, it’s advisable to avoid being anemic at high altitude. Don’t donate blood within four weeks before traveling to high altitude. Iron-deficiency anemia related to menstrual bleeding is common in women. If this is recognized, it should be corrected under the supervision of a physician with 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 necessary). There is a possible increased risk for dangerous hypertension associated with pregnancy (preeclampsia) at high altitude, usually developing after 20 weeks of pregnancy and for up to 1 month after childbirth. Proper acclimatization is essential. Try to keep the sleeping altitude no higher than 10,000 ft (3048 m) and never above 12,000 ft (3658 m). Arterial oxygen saturation measured by pulse oximeter should remain at or above 85%. If a woman has a complicated pregnancy in which her obstetrician has advised caution or restrictions beyond those associated with a normal pregnancy, she should not hike higher than an altitude of 12,000 ft (3658 m). Additionally, ondansetron as an antivomiting drug, which is sometimes used to treat AMS, should probably be avoided in the first trimester of pregnancy if possible, although there is emerging evidence that it is safe.

Regarding children at high altitude, don’t bring children younger than 4 to 6 weeks of age to high altitude. Infants who required supplemental oxygen during the neonatal period are at particular risk for high-altitude illness. Avoid traveling to altitude with children who have suffered recent viral infection or situations associated with high pressure in the lungs’ vascular system. Children with trisomy 21 are more prone to HAPE than are those with normal chromosomes.

Physical fitness, while desirable for mountaineering, does not protect against high-altitude illness. 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 or high altitude-related illness, here are some other general guidelines:

• Probably no extra risk: Extremes of age, obesity, diabetes, stable condition (e.g., no ongoing angina) after coronary artery bypass surgery, mild chronic obstructive pulmonary disease (COPD), controlled asthma, normal (low risk) pregnancy, controlled high blood pressure, controlled seizure disorder, stable psychiatric disorder, cancer, inflammatory diseases

• Caution: Moderate COPD, congestive heart failure, sleep apnea, worrisome irregular heart rhythms, recurrent episodes of angina, sickle cell trait (can suffer splenic infarction), cerebrovascular diseases, abnormal lung circulation, poorly controlled seizure disorder, radial keratotomy

• High risk: high risk pregnancy, sickle cell anemia with history of crises (can suffer splenic infarction), severe COPD, pulmonary hypertension, poorly controlled congestive heart failure, recent unstable heart condition (e.g., abnormal rhythm requiring intervention)

Persons with unstable preexisting neurologic conditions should not travel to high altitude, because resultant low blood oxygen levels might impair or prevent recovery from the condition. Absolute contraindications to active (e.g., trekking or climbing) or passive (e.g., motorized vehicle transport) ascent are an unstable condition, high risk for a repeat stroke, or a transient ischemic attack (TIA, see page 165) within the past 90 days. Persons with a residual “central” neurologic deficit (e.g., from a stroke) or peripheral (e.g., from multiple sclerosis or severe diabetic neuropathy) deficit should not actively ascend, but they may passively ascend. Relative contraindications (speak to your physician for advice) include a severe narrowing or occlusion of a cerebral artery, space-occupying lesion (e.g., brain tumor), poorly controlled seizure disorder, or cerebral aneurysm (dilated blood vessel that might leak or burst). Any person who has suffered a stroke should consult with their physician to determine whether a high-altitude sojourn should be allowed, and if so, if antiplatelet (anti blood clotting) therapy should be started. Persons with dementia should be watched very closely for increase in impairment. Preexisting headaches are not a contraindication for a trip to high altitude.

If a person suffers from any chronic condition, they should clear 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.

HAPE usually occurs in an unacclimatized individual—typically a male—who rapidly ascends to an altitude that exceeds 8000 ft (2438 m), particularly if heavy exertion is involved. Prior traditional physical conditioning is not protective; many cases involve young, previously healthy individuals. If the victim exercises above 8000 ft (2438 m) but sleeps at a lower altitude (such as 6000 ft or 1829 m), their risk for developing HAPE is much less.

Symptoms begin 1 to 3 days after arrival at high altitude. They include decreased exercise tolerance and increased recovery time, shortness of breath (very worrisome if it occurs at rest), cough, weakness, easy fatigue (especially when walking uphill), new inability to keep up with the group, and difficulty sleeping. Signs of AMS (see page 353) are often present. As greater amounts of fluid accumulate in the lungs, the victim develops drowsiness, severe shortness of breath, and rapid heart rate; their initial dry and gentle (“soft”) cough produces white phlegm and then blood (pink, frothy sputum—a late sign); they exhibit 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 might hear crackling or gurgling noises. The symptoms worsen at night. Rapidly, the victim becomes extremely agitated, disoriented, and sweaty; they are in obvious extreme respiratory distress. Confusion, collapse, and coma follow (which might represent coexisting HACE—see below). The victim might 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 early 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 administration of oxygen; if it is available, oxygen at a flow rate of 4 to 6 liters per minute should be administered by face mask (see page 431). Improvement is rarely noted, until oxygen is administered or descent of at least 1640 to 3281 ft (500 to 1000 m) is accomplished. If the victim improves, diminish the flow rate of oxygen to 2 to 4 liters per minute (try to maintain arterial oxygen saturation above 90% as measured by pulse oximeter) to conserve supplies.

In no case should a victim be left to descend by themself. Always have a healthy person accompany them. If the victim must be carried down, they should be kept in a sitting position, if possible. Keep them warm.

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

A drug that may help 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 sustained-release preparation every 12 hours (or 20 mg extended-release every 8 hours). The dose in children for HAPE is 0.5 mg per 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 sustained-release preparation is used. Sildenafil (Viagra) 50 mg by mouth every 8 hours, or tadalafil (Cialis) 10 mg by mouth every 12 hours, has been used to prevent HAPE because of its effect on lowering pressure in part of the circulation within the lungs but has not been well studied for treatment.

Nifedipine has also been used successfully to prevent HAPE in subjects with a history of repeated episodes. The dose for prevention is 20 mg of the extended-release preparation every 8 hours or 30 mg of the extended-release preparation every 12 hours. Other drugs that have been suggested for prevention include tadalafil and sildenafil (see above), and inhaled salmeterol 125 μg by inhalation twice a day (in conjunction with oral medication; not to be used alone for prevention). Dexamethasone in a dose of 8 mg twice a day beginning 2 days before high altitude exposure has been suggested to prevent HAPE, particularly in persons with a history of this condition.

Some aid stations and expedition teams in high-altitude regions are equipped with an inflatable pressure bag (such as a “Gamow bag”) large enough to enclose a human (see page 355). This portable hyperbaric chamber is used to simulate conditions at lower altitude and can be used to treat moderate or severe high-altitude illness including HAPE and HACE. If a Gamow-type bag is used, note that foot pumping to keep it inflated must be continuous, so it’s wise to recruit additional rescuers.

Once a victim has been judged to suffer from any degree of HAPE, they 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

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 might be present in someone who has worsened from AMS (see below) or who is suffering from HAPE. When HACE occurs, it is often after two or more days at an altitude of 13,123 ft (4000 m) or more. The hallmark symptom is staggering (ataxic) gait (difficulty walking: loss of balance, inability to walk a straight line, or frank inability to walk). Symptoms include headache (often throbbing), clumsiness, amnesia, difficulty in speaking, drowsiness, vomiting, mild fever, and, in severe cases, confusion, blurred vision, blindness, unconsciousness, paralysis, and/or coma. Other symptoms might include mood changes, hallucinations, paralysis of an arm and/or leg, and seizures. 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 extremely drowsy person might slip rapidly into a coma. “High-altitude headache” is often the first noxious symptom noted on exposure to high altitude and might be the harbinger of AMS (see later). There is emerging thought that psychosis (see page 317) can be triggered by very high altitude. This would need to be differentiated from HACE.

Treatment for HACE is immediate descent to an altitude below one at which the victim previously had no symptoms, and administration of oxygen at a flow rate of 5 to 10 liters per minute by face mask or nasal cannula (tube) (see page 431). Attempt to descend at least 3000 ft (914 m). If the victim becomes severely ill, they should be brought (carried, if necessary, and preferably in the sitting position) to a lower altitude (below 5000 ft or 1524 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, is often helpful and absolutely indicated. The pediatric dose of dexamethasone is 0.3 mg per kg (2.2 lb) of body weight for the first dose, followed by 0.15 mg per kg (maximum dose 4 mg) every 6 hours. Again, never leave a potentially seriously ill person to fend for themself. 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 (see page 355). Because the early symptoms of AMS (see later) and HACE are similar, pay close attention to the condition of ill members of your climbing party. If all appropriate measures are taken to treat HACE, and the person doesn’t completely recover, they should be evacuated to see if there is another neurological problem, such as a stroke or brain tumor.

If a person has suffered any form of traumatic brain injury (see page 72), it is prudent to allow at least 90 days after resolution of all symptoms before ascending to high altitude. Acclimatization should be very gradual; pre-acclimatization is recommended; and use acetazolamide if there is not time for slow ascent. Be accustomed to the intended exercise and always carry dexamethasone as a “rescue drug” (see above). Anyone with persistent symptoms (even if improving) should not sleep at an altitude above ft (3000 m). If there is any residual fluid collection within the skull (such as hydrocephalus), then be extremely cautious, because brain volume expands with increasing altitude.

Acute mountain sickness

AMS is the most common high altitude–related disorder. It affects persons who ascend to altitudes above 8200 ft (2500 m) from below 4921 ft (1500 m) and are unable to keep pace with acclimatization. A person who is partially acclimatized might be stricken if they ascend rapidly to a higher altitude.

Clinicians and researchers have used the Lake Louise Scoring System for Acute Mountain Sickness to diagnose and score the severity of AMS. It underwent consensus revision in 2017. The current Lake Louise AMS Score is:

• Headache:

  • 0 None

  • 1 Mild headache

  • 2 Moderate headache

  • 3 Severe (incapacitating) headache

• Gastrointestinal symptoms:

  • 0 None

  • 1 Poor appetite or nausea

  • 2 Moderate nausea or vomiting

  • 3 Severe (incapacitating) nausea and vomiting

• Fatigue and/or weakness:

  • 0 Not tired or weak

  • 1 Mild fatigue or weakness

  • 2 Moderate fatigue or weakness

  • 3 Severe (incapacitating) fatigue or weakness

• Dizziness or lightheadedness:

  • 0 None

  • 1 Mild

  • 2 Moderate

  • 3 Severe (incapacitating)

• Overall Functional Score:

  • How did these AMS symptoms affect your activities?

    • 0 Not at all

    • 1 No change in activity or itinerary

    • 2 Symptoms forced me to stop the ascent or to descend under my own power

    • 3 I had to be evacuated to a lower altitude

Symptoms of AMS can start within 2 hours after arrival at altitude and rarely begin after 48 hours at a given altitude. They might be quite subtle in the beginning and are most commonly headache (in its mildest form sometimes called “high-altitude headache”) of a throbbing nature, combined with one or more of the following: fatigue (tiredness), dizziness or lightheadedness, loss of appetite, nausea or vomiting, and frequent awakening during sleep. The headache can be global, located on both sides of the head or in the back of the head; made worse by simultaneously straining and holding one’s breath; and is worse at night or when bending over. Other symptoms include insomnia, poor appetite, nausea, vomiting, drowsiness, dizziness, lightheadedness, weakness, fatigue, and loss of motivation or apathy. Poor sleep is not currently considered a diagnostic criterion for AMS, but anyone who has sudden change in sleep patterns should be watched closely. 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, as well as fussiness, lack of playfulness, poor appetite, and poor sleep. The lips and fingernails might 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 might be complicated by difficulty in walking (particularly if HAPE is present) and impaired memory. The headache is mild to severe and as described earlier. 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 might be so severe that the victim is too apathetic to contribute to their own basic needs. The symptoms of AMS can be confused with dehydration, exhaustion, bacterial or viral infection, hypothermia, carbon monoxide poisoning, migraine headache, low blood sugar, TIA or stroke, illicit drug ingestion, or psychiatric disease.

One cause 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 can pass without a breath. Acetazolamide, 125 mg at bedtime, diminishes periodic breathing, improves oxygenation, and is safe to use as a sleeping aid. Insomnia from other causes might 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. 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 might mask the symptoms of HACE.

Treatment for AMS includes rest, adequate fluid intake to avoid dehydration, light exercise, and mild pain medicine for the headache. First and foremost, do not proceed to a higher sleeping altitude unless all symptoms have completely resolved. Oxygen administration (0.5 to 1.5 liters per minute by nasal cannula or simple open face mask to raise arterial oxygen saturation to greater than 90% as measured by pulse oximeter) might be effective for the headache, as might be acetaminophen or an NSAID. The victim can be led to a lower altitude, preferably at least 1640 to 3281 ft (500 to 1000 m) below that where symptoms began. This should be done particularly when the victim is felt to suffer from severe AMS or does not improve after 24 hours at the altitude where AMS began. 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 and improving. Again, 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. Attempt to descend at least 1500 ft (457 m). The goal is to descend to lowest reasonable possible altitude. 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 2.5 mg per kg (2.2 lb) of body weight every 12 hours, up to 250 mg per dose. Give this medication for 2 days while at altitude or until symptoms have diminished, whichever is shorter.

Prochlorperazine (Compazine) 10 mg by mouth or 25 mg by suppository can be given for nausea and vomiting, with the added benefit that it might stimulate the beneficial ventilatory (breathing) response that is triggered by a low oxygen content in the blood (associated with high altitude and called the “hypoxic ventilatory response”). The dose in children older than 2 years of age is 0.4 mg per 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. Another effective drug is ondansetron (Zofran) 4 mg oral dissolving tablet. Aspirin, acetaminophen, or ibuprofen can be given for headache. Avoid the use of alcohol or other respiratory depressants. Minimize excessive physical exertion.

If an oxygen cylinder is available (see page 431), low-flow (0.5 to 2 liters per minute) oxygen by nasal cannula (tube) or face mask is particularly effective if used for sleep. This alone might 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 (see Gamow bag page 355).

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 and descend to a lower altitude (at least 1640 to 3281 ft (500 to 1000 m). AMS can progress to HACE with coma in less than 24 hours.

As noted previously, 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 might 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 can be used to treat AMS in an adult dose of 8 mg by mouth first dose, then 4 mg every 6 hours. It should optimally be used for no more than 48 hours, during which time descent should be undertaken, from where acclimatization may proceed. A person should not ascend until they are asymptomatic and not taking dexamethasone. At that point, if reascent is attempted, strong consideration should be given to using acetazolamide at an adult dose of 250 mg by mouth twice a day.

Ginkgo biloba administered in a dose of 100 mg by mouth twice a day has been suggested to reduce the incidence of AMS, and perhaps to be helpful as a therapy. This is not as reliable as acetazolamide. Choose a commercial product that has a validated quantity of active ingredient(s).

Untreated, AMS might resolve spontaneously within approximately 3 days. 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 1640 to 3281 ft (500 to 1000 m). The goal is to descend to lowest reasonable possible altitude.

Normally at high altitude as people acclimatize, they urinate more, whether they are taking acetazolamide. They should awaken at least once during the night to urinate. If this does not happen or if they infrequently urinate during the daytime, they might be dehydrated and should be watched closely for signs of AMS.