Some people are more susceptible to altitude sickness than others.
If you suffer from a case of altitude sickness it does not mean that you
can never go to high altitudes again. However, it does mean in the
future, you should pay attention. Awareness of altitude sickness has
caused some trekkers to be unnecessarily anxious as they trek. The
progression of symptoms is usually gradual, and you will have plenty of
time to react appropriately. Design your itineraries to allow plenty of
time for acclimatization so that you will be able to adjust to the
increase in altitude. Human bodies have the ability to adjust to higher
altitudes when given enough time. If a person travels up to high
altitudes more rapidly than his or her body is able to adjust, AMS
symptoms develop.
The treatments of AMS are first and foremost not to ascend with
symptoms and if symptoms are severe, to descend. In rare cases where the
descent is difficult or impossible a portable pressure chamber is
effective. Three medications have also been proven useful for treating
and preventing AMS: Acetazolamide (Diamox), Dexamethasone (Decadron),
Nifedipine. Your physician and local Public Health Service are the best
sources for further information.
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
metres (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 ascend 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 is
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 level, 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, altitudes 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 acclimatisation
occurs. However, in extreme cases, altitude sickness can be fatal.
Signs and symptoms
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 metres (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).
- 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 metres (10,000 feet = 70 kPa), 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
acclimatised 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 (10,000 feet = 70 kPa) to 4,500 meters (15,000
feet = 58 kPa) in one day, but one should then descend back to 3,300
meters (11,000 feet = 67.5 kPa) 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 8,000 feet (2,400 m) as in many Colorado, USA mountain resorts.
Stopping at an intermediate altitude overnight can alleviate or
eliminate occurrences of AMS.
Medical treatment
The drug acetazolamide may help some people making a rapid ascent
to sleeping altitude above 2,700 metres (9,000 ft), and it may also be
effective if started early in the course of AMS. TheEverest 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
suggests a lower dose for prevention of 125 mg acetazolamide every 12
hours. An undesirable side-effect of acetazolamide is a reduction in
aerobic endurance performance. Dosage of 1000 mg/day will produce a 25%
decrease in performance, on top of the reduction due to high-altitude
exposure. 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 (11,155 feet = 67 kPa),
raising the oxygen concentration level by 5 percent via an oxygen
concentrator and an existing ventilation system provides an effective
altitude of 3,000 metres (10,000 feet = 70 kPa), which is more tolerable
for surface-dwellers.
Other methods
Increased water intake may also help in acclimatisation to replace
the fluids lost through heavier breathing in the thin, dry air found at
altitude, although consuming excessive quantities ("over-hydration") 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).
Also, the use of Nitric Oxide has been proven to address and
relieve altitude sickness. 12 scientists recently released a study in
which Mount Everest trekkers were allowed to naturally adapt to altitude
during their ascent. They were tested for nitric oxide levels along the
way. The scientists found that their bodies naturally produced more
nitric oxide as they climbed higher. "Our results suggest that nitric
oxide is an integral part of the human physiological response to
hypoxia." Scientific Reports
Treatment
The only reliable treatment and in many cases the only option
available is to descend. Attempts to treat or stabilise 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.
- Acetazolamide may assist in altitude acclimatization.
- and prevents further impairment of pulmonary gas exchange."
Other treatments include injectable steroids to reduce pulmonary
edema, this may buy time to descend but treats a symptom, it does not
treat the underlying AMS.
