GUIDE TO ACCLIMITIZATION
TREKKING SAFELY AT ALTITUDE
DIAMOX (ACETAZOLAMIDE)
For Your Doctor
Recommended Prophylactic Dose = 125mg/2x Per Day
Recommended Symptomatic Dose = 250mg/2x Per Day
Begin taking Diamox 24 hours before ascent; we recommend taking a full dose of 250 mg/2x per day the day before flying to altitude.
(Leh, Lukla & Nepal Mountain Airports)
125mg of Diamox taking in the evening also helps with sleeping …
AMS
CDC (The Center for Disease Control)
Acute Mountain Sickness
AMS is the most common form of altitude illness, affecting 25% of all visitors sleeping above 8,000’ (2500m). Symptoms are similar to those of a hangover: headache is the cardinal symptom, sometimes accompanied by fatigue, loss of appetite, nausea, and occasionally vomiting. Headache onset is usually 2–12 hours after arrival at a higher elevation and often during or after the first night. Preverbal children may develop loss of appetite, irritability, and pallor. AMS generally resolves with 12–48 hours of acclimatization.
High-Altitude Pulmonary Edema
HAPE can occur by itself or in conjunction with AMS and HACE; incidence is 1 per 10,000 skiers in Colorado and up to 1 per 100 climbers at more than 14,000’ (4270m). Initial symptoms are increased breathlessness with exertion, and eventually increased breathlessness at rest, associated with weakness and cough. Oxygen or descent is lifesaving. HAPE can be more rapidly fatal than HACE.
High-Altitude Cerebral Edema
HACE is a severe progression of AMS and is rare; it is most often associated with HAPE. In addition to AMS symptoms, lethargy becomes profound, with drowsiness, confusion, and ataxia on tandem gait test, similar to alcohol intoxication. A person with HACE requires immediate descent; if the person fails to descend, death can occur within 24 hours of developing ataxia.
AMS ADVICE
Dr Leo Montejo
Diamox
“Speeds up the acclimatization process by forcing your kidneys to secrete bicarbonate, which in turn causes the blood to become more acidic and encourages you to breathe. Because the body equates acidity of the blood to its CO2 concentration, artificially acidifying the blood fools the body into thinking it has an excess of CO2. This misperception causes the body to excrete this perceived excess CO2 by deeper and faster breathing, which in turn increases the amount of oxygen in the blood.”
Sleeping at Altitude
“Lying flat on your back makes your intestines squash your lungs, so you lose about 10% of alveoli depending on your weight. Sleep using a raised pillow.”
Pressure Breathing
“Prevents the alveoli from collapsing at the end of a respiratory cycle, so they work all the time. This raises your SPO about 2-4%.”
AMS
Wikipedia
AMS
Altitude sickness—also known as acute mountain sickness (AMS), altitude illness, hypobaropathy, or soroche—is a pathological effect of high altitude on humans, caused by acute exposure to low partial pressure of oxygen at high altitude. It commonly occurs above 2,400 meters (8,000 feet). It presents as a collection of nonspecific symptoms, acquired at high altitude or in low air pressure, resembling a case of “flu, carbon monoxide poisoning, or a hangover”. It is hard to determine who will be affected by altitude sickness, as there are no specific factors that correlate with a susceptibility to altitude sickness. However, most people can climb up to 2,400 meters (8,000 ft) without difficulty.
Acute mountain sickness can progress to high altitude pulmonary edema (HAPE) or high altitude cerebral edema (HACE), which are potentially fatal. Chronic mountain sickness, also known as Monge’s disease, is a different condition that only occurs after very prolonged exposure to high altitude.
CAUSES
The percentage of oxygen in air, at 21%, remains almost unchanged up to 70,000 feet (21,000 m). The RMS velocities of diatomic nitrogen and oxygen are very similar and thus no change occurs in the ratio of oxygen to nitrogen. However, it is the air density itself, the number of molecules (of both oxygen and nitrogen) per given volume, which drops as altitude increases. Consequently, the available amount of oxygen to sustain mental and physical alertness decreases above 10,000 feet (3,000 m). Although the cabin altitude in modern passenger aircraft is kept to 8,000 feet (2,400 m) or lower, some passengers on long-haul flights may experience some symptoms of altitude sickness.
Dehydration due to the higher rate of water vapor lost from the lungs at higher altitudes may contribute to the symptoms of altitude sickness.
The rate of ascent, altitude attained, amount of physical activity at high altitude, as well as individual susceptibility, are contributing factors to the onset and severity of high-altitude illness.
Altitude sickness usually occurs following a rapid ascent and can usually be prevented by ascending slowly. In most of these cases, the symptoms are temporary and usually abate as altitude acclimatization occurs. However, in extreme cases, altitude sickness can be fatal.
SIGNS & SYMPTOMS
People have different susceptibilities to altitude sickness; for some otherwise healthy people, acute mountain sickness (AMS) can begin to appear at around 2000 meters (6,500 ft) above sea level, such as at many mountain ski resorts, equivalent to a pressure of 80 kPa. AMS is the most frequent type of altitude sickness encountered. Symptoms often manifest themselves six to ten hours after ascent and generally subside in one to two days, but they occasionally develop into the more serious conditions. Symptoms include headache, fatigue, stomach illness, dizziness, and sleep disturbance. Exertion aggravates the symptoms.
The Lake Louise assessment system of AMS is based on a self-report questionnaire as well as a quick clinical assessment. Those individuals with the lowest initial partial pressure of end-tidal pCO2 (the lowest concentration of carbon dioxide at the end of the respiratory cycle) as a measure of a higher alveolar ventilation, as well as individuals with a corresponding high oxygen saturation levels tend to have a lower incidence of Acute Mountain Sickness than those with high end-tidal pCO2 and low oxygen saturation levels.
PRIMARY SYMPTOMS
Headaches are the primary symptom used to diagnose altitude sickness, although a headache is also a symptom of dehydration. A headache occurring at an altitude above 2,400 meters (8,000 feet = 76 kPa), combined with any one or more of the following symptoms, may indicate altitude sickness:
Lack of appetite, nausea, or vomiting
Fatigue or weakness
Dizziness or lightheadedness
Insomnia
Pins and needles
Shortness of breath upon exertion
Nosebleed
Persistent rapid pulse
Drowsiness
General malaise
Peripheral edema (swelling of hands, feet, and face).
Diarrhea
SEVERE SYMPTOMS
Symptoms that may indicate life-threatening altitude sickness include:
Pulmonary edema (fluid in the lungs)
Symptoms similar to bronchitis
Persistent dry cough
Fever
Shortness of breath even when resting
Cerebral edema (swelling of the brain)
Headache that does not respond to analgesics
Unsteady gait
Gradual loss of consciousness
Increased nausea
Retinal hemorrhage
The most serious symptoms of altitude sickness arise from edema (fluid accumulation in the tissues of the body). At very high altitude, humans can get either high altitude pulmonary edema (HAPE), or high altitude cerebral edema (HACE). The physiological cause of altitude-induced edema is not conclusively established. It is currently believed, however, that HACE is caused by local vasodilation of cerebral blood vessels in response to hypoxia, resulting in greater blood flow and, consequently, greater capillary pressures. On the other hand, HAPE may be due to general vasoconstriction in the pulmonary circulation (normally a response to regional ventilation-perfusion mismatches) which, with constant or increased cardiac output, also leads to increases in capillary pressures. For those suffering HACE, dexamethasone may provide temporary relief from symptoms in order to keep descending under their own power.
HAPE can progress rapidly and is often fatal. Symptoms include fatigue, severe dyspnea at rest, and cough that is initially dry but may progress to produce pink, frothy sputum. Descent to lower altitudes alleviates the symptoms of HAPE.
HACE is a life threatening condition that can lead to coma or death. Symptoms include headache, fatigue, visual impairment, bladder dysfunction, bowel dysfunction, loss of coordination, paralysis on one side of the body, and confusion. Descent to lower altitudes may save those afflicted with HACE.
PREVENTION
Ascending slowly is the best way to avoid altitude sickness. Avoiding strenuous activity such as skiing, hiking, etc. in the first 24 hours at high altitude reduces the symptoms of AMS. As alcohol tends to cause dehydration, which exacerbates AMS, avoiding alcohol consumption in the first 24-hours at a higher altitude is optimal.
ALTITUDE ACCLIMATIZATION
Altitude acclimatization is the process of adjusting to decreasing oxygen levels at higher elevations, in order to avoid altitude sickness. Once above approximately 3,000 meters most climbers and high-altitude trekkers take the “climb-high, sleep-low” approach. For high-altitude climbers, a typical acclimatization regimen might be to stay a few days at a base camp, climb up to a higher camp (slowly), and then return to base camp. A subsequent climb to the higher camp then includes an overnight stay. This process is then repeated a few times, each time extending the time spent at higher altitudes to let the body adjust to the oxygen level there, a process that involves the production of additional red blood cells. Once the climber has acclimated to a given altitude, the process is repeated with camps placed at progressively higher elevations. The general rule of thumb is to not ascend more than 300 meters (1,000 ft) per day to sleep. That is, one can climb from 3,000 to 4,500 meters in one day, but one should then descend back to 3,300 meters to sleep. This process cannot safely be rushed, and this is why climbers need to spend days (or even weeks at times) acclimatizing before attempting to climb a high peak. Simulated altitude equipment that produces hypoxic (reduced oxygen) air can be used to acclimate to high altitude, reducing the total time required on the mountain itself.
Altitude acclimatization is necessary for some people who move rapidly from lower altitudes to intermediate altitudes, e.g. by aircraft and ground transportation over a few hours, such as from sea level to 8000 feet (2,400 m) of many Colorado, USA mountain resorts. Stopping at an intermediate altitude overnight can reduce or eliminate an occurrence of AMS.
MEDICAL TREATMENT
The drug acetazolamide may help some people making a rapid ascent to sleeping altitude above 2750 meters, and it may also be effective if started early in the course of AMS. The Everest Base Camp Medical Centre cautions against its routine use as a substitute for a reasonable ascent schedule, except where rapid ascent is forced by flying into high altitude locations or due to terrain considerations. The Centre suggests a dosage of 125–250 mg twice daily for prophylaxis, starting from 24 hours before ascending until a few days at the highest altitude or on descending; with 250 mg twice daily recommended for treatment of AMS. The Centers for Disease Control and Prevention suggest a lower dose for prevention of 125 mg acetazolamide every 12 hours.The CDC advises that Dexamethasone be reserved for treatment of AMS and HACE during descents, and notes that Nifedipine may prevent HAPE.
A single randomized controlled trial found that sumatriptan may help prevent altitude sickness. Despite their popularity, antioxidant treatments have not been found to be effective medications for prevention of AMS. Interest in phosphodiesterase inhibitors such as sildenafil has been limited by the possibility that these drugs might worsen the headache of mountain sickness. A promising possible preventative treatment for altitude sickness is myo-inositol trispyrophosphate (ITPP), which increases the amount of oxygen released by hemoglobin. For centuries, indigenous peoples of the Americas such as the Aymaras of the Altiplano, have chewed coca leaves to try to alleviate the symptoms of mild altitude sickness. In Chinese and Tibetan traditional medicine, extract of root tissue of Radix rhodiola is often taken in order to prevent the same symptoms.
OXYGEN ENRICHMENT
In high-altitude conditions, oxygen enrichment can counteract the hypoxia related effects of altitude sickness. A small amount of supplemental oxygen reduces the equivalent altitude in climate-controlled rooms. At 3,400 meters raising the oxygen concentration level by 5 percent via an oxygen concentrator and an existing ventilation system provides an effective altitude of 3,000 meters, which is more tolerable for surface-dwellers.
OTHER METHODS
Drinking plenty of water will also help in acclimatization to replace the fluids lost through heavier breathing in the thin, dry air found at altitude, although consuming excessive quantities (‘overhydration’) has no benefits and may cause dangerous hyponatremia.
Oxygen from gas bottles or liquid containers can be applied directly via a nasal cannula or mask. Oxygen concentrators based upon pressure swing adsorption (PSA), VSA, or vacuum-pressure swing adsorption (VPSA) can be used to generate the oxygen if electricity is available. Stationary oxygen concentrators typically use PSA technology, which has performance degradations at the lower barometric pressures at high altitudes. One way to compensate for the performance degradation is to utilize a concentrator with more flow capacity. There are also portable oxygen concentrators that can be used on vehicular DC power or on internal batteries, and at least one system commercially available measures and compensates for the altitude effect on its performance up to 4,000 meters (13,000 ft). The application of high-purity oxygen from one of these methods increases the partial pressure of oxygen by raising the FiO2 (fraction of inspired oxygen).
TREATMENT
The only reliable treatment and in many cases the only option available is to descend. Attempts to treat or stabilize the patient in situ at altitude is dangerous unless highly controlled and with good medical facilities. However, the following treatments have been used when the patient’s location and circumstances permit:
Oxygen may be used for mild to moderate AMS below 12,000 feet (3,700 m) and is commonly provided by physicians at mountain resorts. Symptoms abate in 12–36 hours without the need to descend.
For more serious cases of AMS, or where rapid descent is impractical, a Gamow bag, a portable plastic hyperbaric chamber inflated with a foot pump, can be used to reduce the effective altitude by as much as 1,500 meters (5,000 ft). A Gamow bag is generally used only as an aid to evacuate severe AMS patients, not to treat them at altitude.
GUIDE TO ACCLIMATIZATION
Thomas E. Dietz
The Golden Rules
GOLDEN RULE I
If you feel unwell at altitude it is altitude illness until proven otherwise.
GOLDEN RULE II
Never ascend with symptoms of AMS.
GOLDEN RULE III
If you are getting worse (or have HACE or HAPE), go down at once.
Normal Acclimatization
Acclimatization is the process of the body adjusting to the decreased availability of oxygen at high altitudes. It is a slow process, taking place over a period of days to weeks.
– High Altitude: 2500 – 3500m (8200 – 11500’)
– Very High Altitude: 3500 – 5500m (11500 – 18000’)
– Extreme Altitude: above 5500m
Certain normal physiologic changes occur in every person who goes to altitude:
– Hyperventilation (breathing faster, deeper, or both)
– Shortness of breath during exertion
– Changed breathing pattern at night
– Awakening frequently at night
– Increased urination
As one ascends through the atmosphere, barometric pressure decreases (though the air still contains 21% oxygen) and thus every breath contains fewer and fewer molecules of oxygen. One must work harder to obtain oxygen, by breathing faster and deeper. This is particularly noticeable with exertion, such as walking uphill. Being out of breath with exertion is normal, as long as the sensation of shortness of breath resolves rapidly with rest. The increase in breathing is critical. It is therefore important to avoid anything that will decrease breathing, e.g. alcohol and certain drugs. Despite the increased breathing, attaining normal blood levels of oxygen is not possible at high altitude.
Persistent increased breathing results in reduction of carbon dioxide in the blood, a metabolic waste product that is removed by the lungs. The build-up of carbon dioxide in the blood is the key signal to the brain that it is time to breathe, so if it is low, the drive to breathe is blunted (the lack of oxygen is a much weaker signal, and acts as an ultimate safety valve). As long as you are awake it isn’t much trouble to consciously breathe, but at night an odd breathing pattern develops due to a back-and-forth balancing act between these two respiratory triggers. Periodic breathing consists of cycles of normal breathing which gradually slows, breath-holding, and a brief recovery period of accelerated breathing. The breath-holding may last up to 10-15 seconds. This is not altitude sickness. It may improve slightly with acclimatization, but does not usually resolve until descent.
Periodic breathing can cause a lot of anxiety:
– In the person who wakes up during the breath-holding phase and knows he has stopped breathing.
– In the person who wakes up in the post-breath-holding hyperventilation (recovery) phase and thinks he’s short of breath and has High Altitude Pulmonary Edema (HAPE).
– In the person who wakes up and realizes his neighbor has stopped breathing.
In the first two cases waiting a few moments will establish a normal breathing pattern. In the final case, the sleeping neighbor will eventually take a breath, though periodic breathing cycles will likely continue until he or she is awake. If periodic breathing symptoms are troublesome, a medication called acetazolamide may be helpful.
Dramatic changes take place in the body’s chemistry and fluid balance during acclimatization. The osmotic center, which detects the “concentration” of the blood, gets reset so that the blood is more concentrated. This results in an altitude diuresis as the kidneys excrete more fluid. The reason for this reset is not understood, though it has the effect of increasing the hematocrit (concentration of red blood cells) and perhaps improving the blood’s oxygen-carrying ability somewhat; it also counteracts the tendency for edema formation. It is normal at altitude to be urinating more than usual. If you are not, you may be dehydrated, or you may not be acclimatizing well.
Acute Mountain Sickness
Acute Mountain Sickness (AMS) is a constellation of symptoms that represents your body not being acclimatized to its current altitude. As you ascend, your body acclimatizes to the decreasing oxygen (hypoxia). At any moment, there is an “ideal” altitude where your body is in balance; most likely this is the last elevation at which you slept. Extending above this is an indefinite gray zone where your body can tolerate the lower oxygen levels, but to which you are not quite acclimatized. If you get above the upper limit of this zone, there is not enough oxygen for your body to function properly, and symptoms of hypoxic distress occur – this is AMS. Go too high above what you are prepared for, and you get sick.
This “zone of tolerance” moves up with you as you acclimatize. Each day, as you ascend, you are acclimatizing to a higher elevation, and thus your zone of tolerance extends that much higher up the mountain. The trick is to limit your daily upward travel to stay within that tolerance zone.
The exact mechanisms of AMS are not completely understood, but the symptoms are thought to be due to mild swelling of brain tissue in response to the hypoxic stress. If this swelling progresses far enough, significant brain dysfunction occurs (See next section, on HACE). This brain tissue distress causes a number of symptoms; universally present is a headache, along with a variety of other symptoms.
The diagnosis of AMS is made when a headache, with any one or more of the following symptoms is present after a recent ascent above 2500 meters (8000 feet):
– Loss of appetite, nausea, or vomiting
– Fatigue or weakness
– Dizziness or light-headedness- Difficulty sleeping
All of these symptoms may vary from mild to severe. A scoring system has been developed based on the Lake Louise criteria; look at the AMS questionnaire for a simple method to evaluate an individual’s AMS severity. AMS has been likened to a bad hangover, or worse. However, because the symptoms of mild AMS can be somewhat vague, a useful rule-of-thumb is: if you feel unwell at altitude, it is altitude sickness unless there is another obvious explanation (such as diarrhea).
Anyone who goes to altitude can get AMS. It is primarily related to individual physiology (genetics) and the rate of ascent; there is no significant effect of age, gender, physical fitness, or previous altitude experience. Some people acclimatize quickly, and can ascend rapidly; others acclimatize slowly and have trouble staying well even on a slow ascent. There are factors that we don’t understand; the same person may get AMS on one trip and not another despite an identical ascent itinerary. Unfortunately, no way has been found to predict who is likely to get sick at altitude.
It is remarkable how many people mistakenly believe that a headache at altitude is “normal”; it is not. Denial is also common – be willing to admit that you have altitude illness, that’s the first step to staying out of trouble. It is OK to get altitude illness, it can happen to anyone. It is not OK to die from it. With the information in this tutorial, you should be able to avoid the severe, life threatening forms of altitude illness.
High Altitude Cerebral Edema (HACE)
AMS is a spectrum of illness, from mild to life-threatening. At the “severely ill” end of this spectrum is High Altitude Cerebral Edema; this is when the brain swells and ceases to function properly. HACE can progress rapidly, and can be fatal in a matter of a few hours to one or two days. Persons with this illness are often confused, and may not recognize that they are ill.
The hallmark of HACE is a change in mentation, or the ability to think. There may be confusion, changes in behavior, or lethargy. There is also a characteristic loss of coordination that is called ataxia. This is a staggering walk that is similar to the way a person walks when very intoxicated on alcohol. This loss of coordination may be subtle, and must be specifically tested for. Have the sick person do a straight line walk (the “tandem gait test”). Draw a straight line on the ground, and have them walk along the line, placing one foot immediately in front of the other, so that the heel of the forward foot is right in front of the toes behind. Try this yourself. You should be able to do it without difficulty. If they struggle to stay on the line (the high-wire balancing act), can’t stay on it, fall down, or can’t even stand up without assistance, they fail the test and should be presumed to have HACE.
Immediate descent is the best treatment for HACE. This is of the utmost urgency, and cannot wait until morning (unfortunately, HACE often strikes at night). Delay may be fatal. The moment HACE is recognized is the moment to start organizing flashlights, helpers, porters, whatever is necessary to get this person down. Descent should be to the last elevation at which they woke up feeling well. Bearing in mind that the vast majority of cases of HACE occur in persons who ascend with symptoms of AMS, this is likely to be the elevation at which the person slept two nights previously. If you are uncertain, a 500-1000 meter descent is a good starting point. Other treatments include oxygen, hyperbaric bag, and dexamethasone. These are usually used as temporizing measures until descent can be effected (see physician section for more details).
People with HACE usually survive if they descend soon enough and far enough, and usually recover completely. The staggering gait may persist for days after descent. Once recovery has been complete, and there are no symptoms, cautious re-ascent is acceptable.
High Altitude Pulmonary Edema (HAPE)
Another form of severe altitude illness is High Altitude Pulmonary Edema, or fluid in the lungs. Though it often occurs with AMS, it is not felt to be related and the classic signs of AMS may be absent.
Signs and symptoms of HAPE include any of the following:
– Extreme fatigue
– Breathlessness at rest
– Fast, shallow breathing
– Cough, possibly productive of frothy or pink sputum
– Gurgling or rattling breaths
– Chest tightness, fullness, or congestion
– Blue or gray lips or fingernails
– Drowsiness
HAPE usually occurs on the second night after an ascent, and is more frequent in young, fit climbers or trekkers. In some persons, the hypoxia of high altitude causes constriction of some of the blood vessels in the lungs, shunting all of the blood through a limited number of vessels that are not constricted. This dramatically elevates the blood pressure in these vessels and results in a high-pressure leak of fluid from the blood vessels into the lungs. Exertion and cold exposure can also raise the pulmonary blood pressure and may contribute to either the onset or worsening of HAPE.
Immediate descent is the treatment of choice for HAPE; unless oxygen is available delay may be fatal. Descend to the last elevation where the victim felt well upon awakening. Descent may be complicated by extreme fatigue and possibly also by confusion (due to inability to get enough oxygen to the brain); HAPE frequently occurs at night, and may worsen with exertion. These victims often need to be carried. It is common for persons with severe HAPE to also develop HACE, presumably due to the extremely low levels of oxygen in their blood (equivalent to a continued rapid ascent).
HAPE resolves rapidly with descent, and one or two days of rest at a lower elevation may be adequate for complete recovery. Once the symptoms have fully resolved, cautious re-ascent is acceptable.
HAPE can be confused with a number of other respiratory conditions:
High Altitude Cough and Bronchitis are both characterized by a persistent cough with or without sputum production. There is no shortness of breath at rest, no severe fatigue. Normal oxygen saturations (for the altitude) will be measured if a pulse oximeter is available.
Pneumonia can be difficult to distinguish from HAPE. Fever is common with HAPE and does not prove the patient has pneumonia. Coughing up green or yellow sputum may occur with HAPE, and both can cause low blood levels of oxygen. The diagnostic test (and treatment) is descent – HAPE will improve rapidly. If the patient does not improve with descent, then consider antibiotics. HAPE is much more common at altitude than pneumonia, and more dangerous; many climbers have died of HAPE when they were mistakenly treated for pneumonia. Asthma might also be confused with HAPE. Fortunately, asthmatics seem to do better at altitude than at sea-level. If you think it’s asthma, try asthma medications, but if the person does not improve fairly quickly assume it is HAPE and treat it accordingly.
Treating Acute Mountain Sickness
The mainstay of treatment of AMS is rest, fluids, and mild analgesics: acetaminophen (paracetamol), aspirin, or ibuprofen. These medications will not cover up worsening symptoms. The natural progression for AMS is to get better, and often simply resting at the altitude at which you became ill is adequate treatment. Improvement usually occurs in one or two days, but may take as long as 3-4 days. Descent is also an option, and recovery will be quite rapid.
A frequent question is how to tell if a headache is due to altitude. See Golden Rule I. Altitude headaches are usually nasty, persistent, and frequently there are other symptoms of AMS; they tend to be frontal (but may be anywhere), and may worsen with bending over. However, there are other causes of headaches, and you can try a simple diagnostic/therapeutic test. Dehydration is a common cause of headache at altitude. Drink one liter of fluid, and take some acetaminophen or one of the other analgesics listed above. If the headache resolves quickly and totally (and you have no other symptoms of AMS) it is very unlikely to have been due to AMS.
Acetazolamide (DIAMOX)
Acetazolamide (Diamox®) is a medication that forces the kidneys to excrete bicarbonate, the base form of carbon dioxide; this re-acidifies the blood, balancing the effects of the hyperventilation that occurs at altitude in an attempt to get oxygen. This re-acidification acts as a respiratory stimulant, particularly at night, reducing or eliminating the periodic breathing pattern common at altitude. Its net effect is to accelerate acclimatization. Acetazolamide isn’t a magic bullet, cure of AMS is not immediate. It makes a process that might normally take about 24-48 hours speed up to about 12-24 hours.
Acetazolamide is a sulfonamide medication, and persons allergic to sulfa medicines should not take it. Common side effects include numbness, tingling, or vibrating sensations in hands, feet, and lips. Also, taste alterations, and ringing in the ears. These go away when the medicine is stopped. Since acetazolamide works by forcing a bicarbonate diuresis, you will urinate more on this medication. Uncommon side effects include nausea and headache. A few trekkers have had extreme visual blurring after taking only 1-2 doses of acetazolamide; fortunately they recovered their normal vision in several days once the medicine was discontinued.
Acetazolamide Use & Dosage
For treatment of AMS | 250 mg every 12 hours. The medicine can be discontinued once symptoms resolve. Children may take 2.5 mg/kg body weight every 12 hours.
For Periodic Breathing | 125 mg about an hour before bedtime. The medicine should be continued until you are below the altitude where symptoms became bothersome.
Myths about Acetazolamide
MYTH: Acetazolamide hides symptoms
Acetazolamide accelerates acclimatization. As acclimatization occurs, symptoms resolve, directly reflecting improving health. Acetazolamide does not cover up anything. If you are still sick, you will still have symptoms. If you feel well, you are well.
MYTH: Acetazolamide will prevent AMS from worsening during ascent
Acetazolamide DOES NOT PROTECT AGAINST WORSENING AMS WITH CONTINUED ASCENT. It does not change Golden Rule II. Plenty of people have developed HAPE and HACE who believed this myth.
MYTH: Acetazolamide will prevent AMS during rapid ascent
This is actually not a myth, but rather a misused partial truth. Acetazolamide does lessen the risk of AMS, that’s why we recommend it for people on forced ascents. This protection is not absolute, however, and it is foolish to believe that a rapid ascent on acetazolamide is without serious risk. Even on acetazolamide, it is still possible to ascend so rapidly that when illness strikes, it may be sudden, severe, and possibly fatal.
MYTH: If Acetazolamide is stopped, symptoms will worsen
There is no rebound effect. If acetazolamide is stopped, acclimatization slows down to your own intrinsic rate. If AMS is still present, it will take somewhat longer to resolve; if not – well, you don’t need to accelerate acclimatization if you ARE acclimatized. You won’t become ill simply by stopping acetazolamide.
Dexamethasone (Decadron®)
Dexamethasone is a potent steroid used to treat brain edema. Whereas acetazolamide treats the problem (by accelerating acclimatization), dexamethasone treats the symptoms (the distress caused by hypoxia). Dexamethasone can completely remove the symptoms of AMS in a few hours, but it does not help you acclimatize. (There are recent studies specifying that Dexamethazone might actually help with acclimatization – KJ). If you use dexamethasone to treat AMS you should not go higher until the next day, to be sure the medication has worn off and is not hiding a lack of acclimatization. Side effects include euphoria in some people, trouble sleeping, and an increased blood sugar level in diabetics.
Dexamethasone Use & Dosage
For treatment of AMS: Two doses of 4 mg, 6 hours apart. This can be given orally, or
by an injection if the patient is vomiting. Children may be given 1 mg/kg of body weight, up to 4 mg maximum; a second dose is given in 6 hours. Do not ascend until at least 12 hours after the last dose, and then only if there are no symptoms of AMS.
Oxygen
AMS symptoms resolve very rapidly (minutes) on moderate-flow oxygen (2-4 liters per minute, by nasal cannula). There may be rebound symptoms if the duration of therapy is inadequate – several hours of treatment may be needed. In most high altitude environments, oxygen is a precious commodity, and as such is usually reserved for more serious cases of HACE and HAPE.
Hyperbaric Therapy (PAC Bag)
Treatment in a portable hyperbaric bag (see physician’s section for details) is essentially equivalent to descent or treatment with oxygen; the person is inside a pressurized bag breathing an atmosphere equivalent to a much lower altitude. AMS symptoms rapidly resolve (minutes), but may recurr if treatment is too short – at least two hours are needed. Dexamethasone works as well, though not quite as fast, is much cheaper, and far less labor-intensive than hyperbaric therapy. Hyperbaric treatment is usually reserved for more serious cases such as HACE and HAPE.
A Review of the AMS Treatment Options
Descent
Pro Rapid recovery: trekkers generally improve during descent, recover totally within several hours.
Con Loss of “progress” toward trek goal; descent may be difficult in bad weather or at night; personnel needed to accompany patient.
Rest – Same Elevation
Pro: Acclimatization to current altitude, no loss of upward progress.
Con: It may take 24-48 hours to become symptom-free.
Rest & Acetazolamide
Pro: As with rest alone, acclimatization is accelerated, recovery likely within 12- 24 hours.
Con: Recovery may take 12-24 hours; side effects of acetazolamide.
Rest & Dexamethasone
Pro: Faster resolution of symptoms than with acetazolamide (usually in a few hours); minimal side effects; cheap.
Con: Can hide symptoms & thus give a false sense of security to those who want to continue upwards.
Rest & Dexamethasone & Acetazolamide
Pro: Fast resolution of symptoms from the dexamethasone, plus improved acclimatization from the acetazolamide.
Con: Side effects of acetazolamide. Same cautions as above regarding ascent after taking dexamethasone.
Oxygen or Hyperbaric Therapy
Pro: Very rapid relief of symptoms (minutes)
Con: Expensive; hyperbaric bags are very labor-intensive; rebound symptoms may
occur if treatment is too short – several hours are needed.
Preventing AMS
The key to avoiding AMS is a gradual ascent that gives your body time to acclimatize. People acclimatize at different rates, so no absolute statements are possible, but in general, the following recommendations will keep most people from getting AMS:
– If possible, you should spend at least one night at an intermediate elevation below 3000 meters.
– At altitudes above 3000 meters (10,000 feet), your sleeping elevation should not increase more than 300-500 meters (1000-1500 feet) per night.
– Every 1000 meters (3000 feet) you should spend a second night at the same elevation.
Remember, it’s how high you sleep each night that really counts; climbers have understood this for years, and have a maxim “climb high, sleep low”. The day hikes to higher elevations that you take on your “rest days” (when you spend a second night at the same altitude) help your acclimatization by exposing you to higher elevations, then you return to a lower (safer) elevation to sleep. This second night also ensures that you are fully acclimatized and ready for further ascent.
Things to Avoid
Respiratory depression (the slowing down of breathing) can be caused by various medications, and may be a problem at altitude. The following medications can do this, and should never be used by someone who has symptoms of altitude illness (these may be safe in persons who are not ill, although this remains controversial):
– Alcohol
– Sleeping pills (acetazolamide is the sleeping tablet of choice at altitude)
– Narcotic pain medications in more than modest doses
AMS Prophylaxis
Under certain circumstances, prophylaxis with medication may be advisable.
– For persons on forced rapid ascents (such as flying into Lhasa, Tibet, or La Paz, Bolivia), for climbers who cannot avoid a big altitude gain due to terrain considerations, or for rescue personnel on a rapid ascent
– For persons who have repeatedly had AMS in the past
Acetazolamide (Diamox)
It carries the risk of any of the severe side effects that may occur with sulfonamides. The dose of acetazolamide for prophylaxis is 125-250 mg twice a day starting 24 hours before ascent, and discontinuing after the second or third night at the maximum altitude (or with descent if that occurs earlier). Sustained release acetazolamide, 500 mg, is also available and may be taken once per day instead of the shorter acting form, though side effects will be more prominent with this dose.
Ginkgo Biloba Extract
Early work with Ginkgo biloba extract was encouraging with regards to its use in preventing AMS, but some recent well-designed studies have shown no benefit.
AMS Prophylaxis
Acetazolamide (Diamox®) 125-250 mg (depending on body weight; persons over 100 kg (220 lbs) should take the higher dose) twice a day starting 24 hours before ascent, and discontinuing after the second or third night at the maximum altitude (or with descent if that occurs earlier). Children may take 2.5 mg/kg of body weight twice a day.
Preventing Severe AMS
This simply cannot be emphasized too much. If you have symptoms of AMS, DO NOT ASCEND ANY HIGHER. Violating this simple rule has resulted in many tragic deaths. If you ascend with AMS you will get worse, and you might die. This is extremely important – even a day hike to a higher elevation is a great risk. In many cases of High Altitude Cerebral Edema, this rule was violated. Stay at the same altitude (or descend) until your symptoms completely go away. Once your symptoms are completely gone, you have acclimatized and then it is OK to continue ascending. It is always OK to descend, you will get better faster.