Altitude Sickness

AMS: Acute Mountain Sickness

Definition: Acute mountain sickness, also known as altitude sickness or soroche, is a collection of non-specific symptoms which quickly transforms to illness (e.g. HAPE or HACE) that can affect mountain climbers, hikers, skiers or travelers who climb too fast. It usually occurs when people rapidly reach a high altitude, typically above 2,400 meters (8,000 feet), or in very low air pressure.

Causes: Acute mountain sickness occurs from the combination of reduced air pressure and a lower concentration of oxygen at high altitude which leads to higher rate of water vapor loss from lungs and fluid loss from brain that further leads to decreased mental and physical alertness.

Symptoms: Symptoms can range from mild to life-threatening and can affect the nervous system, lungs, muscles and heart.

In most cases the symptoms are mild. In severe cases fluid collects in the lungs (pulmonary edema) causing extreme shortness of breath, which further reduces how much oxygen a person gets. Brain swelling may also occur (cerebral edema). This can cause confusion, coma and if untreated, death.

The chance of getting acute mountain sickness increases the faster a person climbs to a high altitude. The severity of the symptoms also depend on this factor, as well as how hard the person pushes (exerts) himself or herself. People who normally live at or near sea level are more prone to acute mountain sickness.

Approximately 20% of people will develop mild symptoms at altitudes between 2400 to 3000 meters, but pulmonary and cerebral edema is extremely rare at these heights. However, above 4200 meters, a majority of people will experience at least mild symptoms. Some people who stay at this height can develop pulmonary or cerebral edema.

Symptoms generally associated with mild to moderate altitude illness include:

  1. Difficulty sleeping
  2. Dizziness or lightheadedness
  3. Swelling of hands, feet, and face
  4. Fatigue or weakness
  5. Headache
  6. Loss of appetite
  7. Nausea or vomiting
  8. Rapid pulse (heart rate)
  9. Shortness of breath with exertion

Symptoms generally associated with more severe altitude illness include:

  1. Bluish discoloration of the skin
  2. Chest tightness or congestion
  3. Confusion
  4. Cough
  5. Coughing up blood
  6. Decreased consciousness
  7. Grey or pale complexion (cerebral edema)
  8. Inability to walk in a straight line
  9. Shortness of breath at rest

Treatment: The main form of treatment for all forms of mountain sickness is to climb down (descend) to a lower altitude as rapidly and as safely as possible. Supplemental oxygen should also be given, if available.

People with severe mountain sickness may be admitted to a hospital.

Portable hyperbaric chambers have been developed to allow hikers to simulate their conditions at lower altitudes without moving from their location on the mountain. These new devices are very important if bad weather or other factors make climbing down the mountain impossible.

Prevention: Education of mountain travelers before ascent is the key to prevention. Basic principles include: gradual ascent, stopping for a day or two of rest for each 600 meters above 2400 meters; sleeping at a lower altitude when possible; and learning how to recognize early symptoms so you can return to lower altitude before worsening symptoms occur.

Mountaineering parties traveling above 3000 meters should carry an oxygen supply sufficient for several days.

Acetazolamide (Diamox) helps speed the process of getting used to higher altitude, and reduces minor symptoms. Therapy should start one day before the ascent and continue one to two days into the excursion. This measure is recommended for those making a rapid ascent to high altitudes.

Drink enough fluids, avoid alcohol and eat regularly. Foods should be relatively high in carbohydrates. People with underlying cardiac or pulmonary (lung) diseases should avoid high altitudes.

CMS: Chronic Mountain Sickness

Chronic mountain sickness is a disease that can develop during extended time living at altitude. It is also known as ‘Monge’s disease’. While acute mountain sickness is experienced shortly after ascent to high altitude, chronic mountain sickness may develop after many years of living at high altitude. In medicine, high altitude is defined as over 2400 meters, but most cases of CMS occur at over 3000 meters.

CMS is characterized by polycythaemia and hypoxemia which both decrease on descent from altitude. CMS is believed to arise because of an excessive production of red blood cells, which increases the oxygen carrying capacity of the blood but may cause increased blood viscosity and uneven blood flow through the lungs. However, CMS is also considered an adaptation of pulmonary and heart disease to life under chronic hypoxia at altitude.

The most frequent symptoms and signs of CMS are headache, dizziness, tinnitus, breathlessness, palpitations, sleep disturbance, fatigue, anorexia, mental confusion, cyanosis, and dilation of veins.

Treatment involves descent from altitude, where the symptoms will diminish and the haematocrit return to normal slowly. Acute treatment at altitude involves bleeding, removal of circulating blood, to reduce the haematocrit; however this is not ideal for extended periods.

HAPE: High Altitude Pulmonary Edema

Definition: HAPE is a life threatening form of non-cardiogenic pulmonary edema resulting in swelling and/or extra vascular fluid accumulation in the air sacs of the lungs, due to leaky capillaries. It severely restrain the supply of oxygen in the lungs, which can result in death in adverse situations.

Sufferer: Often occurs to un-acclimatized mountaineers and trekkers exposed to high altitude above 2500 meters. Some cases have also been reported at lower altitudes between 1500 and 2500 meters.

Cause: HAPE is caused by continuous exposure to low air temperature, shortage of oxygen in blood, low atmospheric air pressure and sometimes by pulmonary hypertension. It depends on the rate of ascent, highest altitude gained, amount of physical stress at high altitude, and individual susceptibility are major factors to the severity of the illness.

Symptoms: Symptoms are: difficulty in breathing and breathlessness even at rest, very high pulse, crackling sound in chest, cough with sputum and sometimes blood, excessive sweating, anxiety and pale skin, severe weakness.

Treatment: If left untreated, it can lead to coma and even death. The standard and most important treatment is immediate descend to lower altitude as quickly as possible, preferably by at least 1000 meters. Oxygen should also be given if possible. Symptoms tend to quickly improve with descend, but less severe symptoms may continue for several days. Drug treatments that may be useful include Acetazolamide*.

*Drug Explanation:

Acetazolamide (e.g. Diamox) is sometimes taken any dose between 125 mg to 500 mg per day, preferably half pill two times a day after food, starting a few days before going to the higher altitude. Such use is recommended for those ascending from sea level to 3000 meters in one day, or for those ascending more than 600 meters per day once above an altitude of 2500 meters. Also this drug use is recommended for those with a significant history of acute mountain sickness.

The drug forces the kidneys to excrete bicarbonate, the conjugate base of carbonic acid. By increasing the amount of bicarbonate excreted in the urine, the blood becomes more acidic. Acidifying the blood stimulates ventilation, which is beneficial during acclimatization.

Note that Acetazolamide is not an immediate fix for acute mountain sickness; it just speeds up acclimatization, which in turn helps to relieve symptoms. This may take up to a day or two, and requires waiting without any further rapid ascent. It is often advisable to descend if even mild acute mountain sickness is experienced. If serious sickness is encountered, descend is considered mandatory unless other circumstances present greater danger.

HACE: High Altitude Cerebral Edema

Definition: HACE is a severe form of altitude sickness resulting swelling of brain tissues from unnecessary fluid leakage, which further progress to severe headache, lack of coordination, vomiting, and coma/death if untreated.

Sufferer: Often occurs to un-acclimatized mountaineers and trekkers exposed to high altitude above 2500 meters for a week or more.

Cause: HACE is caused by continuous exposure to low air temperature, shortage of oxygen in blood, low atmospheric air pressure and fast ascend at steep terrains.

Symptoms: Symptoms are: headache and acute headache, repeated nausea and vomiting, loss of coordination, weakness, decreasing level of consciousness including disorientation, lack of coordination, irritability, lethargy, loss of memory, hallucination, and irrational behavior.

Treatment: If left untreated, it can lead to coma and even death. The standard and most important treatment is immediate descend to lower altitude as quickly as possible, preferably by at least 1000 meters. Symptoms tend to quickly improve with descend. Medication exists that may be prescribed for treatment in the field, is Dexamethasone*

*Drug Explanation:

Dexamethasone (e.g. Decadron) is sometimes taken orally any dose between 0.5 to 1.5 mg per day. Severe side effects encountered in case of dose taken greater than 1.5 mg in a day. This drug use is recommended for only after being affected by acute mountain sickness including HAPE and HACE. Anti-acidic pills may be necessary for those having intensity to acidic stomach.

HAFE: High Altitude Flatus Expulsion

HAFE or High Altitude Flatus Expulsion is a gastrointestinal syndrome which involves the spontaneous passage of increased quantities of rectal gases at high altitudes.

It is based on the differential in atmospheric pressure, directly correlated to the sufferer’s frequency of and level of experience in high-altitude metabolism. As the external pressure decreases, the pressure within the body is relatively higher, and the urge to expel gas to relieve the pressure is relatively greater. The amount of gas produced is constant in weight, but the volume increases when the pressure diminishes.

The feeling of fullness or need to expel brought on by this differential in atmospheric pressure has been verified by studies.

The condition is also known by backpackers as High Altitude Gas (HAG). Another name is Boyle’s disease.

Very rarely encountered by hikers.

Hypothermia: Frostbite

Definition: Hypothermia referred as Frostbite is the medical condition whereby damage is caused to skin and other tissues due to extreme cold.

Cause: At or below 0º C (32°F), blood vessels close to the skin start to narrow. This helps to preserve core body temperature. In extreme cold or when the body is exposed in cold for long periods, this protective strategy can reduce blood flow in some areas of the body to dangerously low levels. The combination of cold temperature and poor blood flow can cause severe tissue injury by freezing the tissue.

Frostbite is most likely to happen in body parts farthest from the heart, and those with a lot of surface area exposed to cold. The initial stages of frostbite are sometimes called “frost-nip”. Mountains or high altitudes with snow are often where the most serious causes of frostbite occur. Nerve damage will occur due to lack of oxygen.

Symptoms: Frostbitten areas will turn discolored, purplish at first, and soon turn black. After a while nerve damage becomes so great that feeling is lost in the frostbitten areas. Blisters will also occur.

Treatment: If frostbite is not treated immediately then the damage and the frostbite become permanent. If feeling is lost in the damaged area, checking it for cuts and breaks in the skin is vital. Infected open skin can lead to Gangrene and Amputation may be needed. To treat frostbite, move the victim to a warm location and seek medical help. Soak frostbitten areas in warm (not hot) water or if in wilderness, warm by contact with the skin of a non-frostbitten person. Continue until the victim has regained sensation and movement in the affected region; this often follows great pain as the nerves thaw. Never rub, slap or shake the stricken region as ice crystals in the frostbitten skin will damage surrounding tissues. Follow the treatment with a period of constant warmth: refreezing following thawing worsens the damage.

Prevention: Factors that contribute to frostbite include extreme cold, inadequate clothing, wet clothes, wind chill, and poor circulation. Poor circulation can be caused by tight clothing or boots, cramped positions, fatigue, certain medications, smoking, alcohol use or diseases that affect the blood vessels, such as diabetes. If caught in a severe snowstorm or other outdoor situation in very cold weather, it is important to find shelter early. This is especially important if the weather is windy, as wind chill can greatly reduce the time it takes for frostbite to set in. Even a small cave, ditch or hollow tree can help reduce the chances of frostbite. It is also important to increase physical activity to maintain body warmth, especially the hands and feet. If without gloves or with inadequate gloves, hands should be kept inside clothing next to the body to stay warm. Extra clothing such as scarves or underwear can be placed around the toes. The face, especially the nose, should be covered with a scarf or other garment. Sharing a sleeping bag or blanket with one or more other people can help to keep warm. In a survival situation, if one person has hypothermia or frostbite, it is recommended for that person to share a sleeping bag with another person (after removing boots, outer clothing, wet clothing, etc.) to gradually warm the victim.

People susceptible to frostbite should wear woolen socks, gloves, and caps in extreme cold. For frostbite in the feet, keeping feet in warm saline water will provide relief. Diabetes can also sometimes lead to frostbite, so diabetics should take precautions as to avoid trips to ice-cold places.

Hyperthermia: Heat Stroke

Definition: Hyperthermia, in its advanced state referred to as heat stroke or sunstroke, is an acute condition which occurs when the body produces or absorbs more heat than it can dissipate. It is usually caused by prolonged exposure to high temperatures. The heat-regulating mechanisms of the body eventually become overwhelmed and unable to effectively deal with the heat, causing the body temperature to climb uncontrollably. Hyperthermia is a medical emergency which requires immediate treatment.

Cause: Hyperthermia can be created artificially by drugs or medical devices. In these instances it may be used to treat cancer and other conditions. Malignant hyperthermia is a rare complication of some types of general anesthesia.
The opposite of hyperthermia is hypothermia, caused when an organism’s temperature drops below that required for normal metabolism. Hypothermia is caused by prolonged exposure to low temperatures and is also a medical emergency requiring immediate treatment.

Symptoms: One of the body’s most important methods of temperature regulation is perspiration. This process draws heat from inside, allowing it to be carried off by radiation or convection. Evaporation of the sweat furthers cooling, since this endothermic process draws yet more heat from the body. When the body becomes sufficiently dehydrated to prevent the production of sweat this avenue of heat reduction is closed. When the body is no longer capable of sweating core temperature begins to rise swiftly.

Victims may become confused, may become hostile, often experience headache, and may seem intoxicated. Blood pressure may drop significantly from dehydration, leading to possible fainting or dizziness, especially if the victim stands suddenly. Heart rate and respiration rate will increase (tachycardia and tachypnea) as blood pressure drops and the heart attempts to supply enough oxygen to the body. The skin will become red as blood vessels dilate in an attempt to increase heat dissipation. The decrease in blood pressure will cause blood vessels to contract as heat stroke progresses, resulting in a pale or bluish skin color. Complaints of feeling hot may be followed by chills and trembling, as is the case in fever. Some victims, especially young children, may suffer convulsions. Acute dehydration such as that accompanying heat stroke can produce nausea and vomiting; temporary blindness may also be observed. Eventually, as body organs begin to fail, unconsciousness and coma will result.

Treatment: Heat stroke is a medical emergency requiring hospitalization, and the local emergency services should be notified as soon as possible.

The body temperature must be lowered immediately. The patient should be moved to a cool area (indoors, or at least in the shade) and clothing removed to promote heat loss (passive cooling). Active cooling methods may be used: The person is bathed in cool water, a hyperthermia vest can be applied, and however, wrapping the patient in wet towels or clothes can actually act as insulation and increase the body temperature. Cold compresses to the torso, head, neck, and groin will help cool the victim. A fan may be used to aid in evaporation of the water (evaporative method).
Immersing a patient into a bathtub of cool – but not cold – water (immersion method) is a recognized method of cooling. This method requires the effort of 4-5 persons and the patient should be monitored carefully during the treatment process. This should be avoided for an unconscious patient; if there is no alternative, the patient’s head must be held above water. Be careful not to make the water too cold as Immersion in ice or very cold water is dangerous as this may cause vasoconstriction in the skin, preventing heat from escaping the body core.

Hydration is of paramount importance in cooling the patient. This is achieved by drinking water (Oral re-hydration). Commercial isotonic drinks may be used as a substitute. Some authorities are opposed to giving any fluids, except by emergency personnel. Intravenous hydration (via a drip) is necessary if the patient is confused, unconscious, or unable to tolerate oral fluids.

Alcohol rubs will cause further dehydration and impairment of consciousness and should be avoided. The patient’s condition should be reassessed and stabilized by trained medical personnel. The patient’s heart rate and breathing should be monitored, and CPR may be necessary if the patient goes into cardiac arrest.
The patient should be placed into the recovery position to ensure that the person’s airway remains open.

Prevention: The risk of heatstroke can be reduced by observing precautions to avoid overheating and dehydration. Light, loose-fitting clothing will allow perspiration to evaporate. Wide-brimmed hats in bright color keep the sun from warming the head and neck; vents on a hat will allow perspiration to cool the head. Strenuous exercise should be avoided during daylight hours in hot weather; so should remaining in enclosed spaces (such as automobiles). People who must be outside should be aware that humidity and the presence of direct sunlight may cause the heat index to be 10 °C (18 °F) hotter than the temperature indicated by a thermometer.

In hot weather people need to drink plenty of liquids to replace fluids lost from sweating. Thirst is not a reliable sign that a person needs fluids. A better indicator is the color of urine. A dark yellow color indicates dehydration. Water, not sports drinks, is the most effective in replacing lost fluids. However, drinking only water without ingesting any salts will lead to a condition known as hypernatremia, which can cause sudden death from heart attack. Humans lose electrolytes through sweat and urine which also need to be replaced along with fluids.

Hypo hydration: Dehydration

Definition: Hypo hydration or Dehydration is the excessive loss of water from the body. In physiological terms, it entails a relative deficiency of water molecules in relation to other dissolved solutes.


  1. Prolonged physical activity without consuming adequate water
  2. Prolonged exposure to dry air
  3. Survival situations, especially desert conditions
  4. Hypotension due to physical trauma
  5. Diarrhea
  6. Hyperthermia
  7. Shock
  8. Vomiting
  9. Burns
  10. Lacrimation
  11. Use of stimulants
  12. Drinking of Alcohol

Symptoms: Symptoms may include headaches similar to what is experienced during a hangover, muscle cramps, a sudden episode of visual snow, decreased blood pressure (hypotension), and dizziness or fainting when standing up due to orthostatic hypotension.

Dehydration symptoms generally become noticeable after 2% of one’s normal water volume has been lost. Initially, one experiences thirst and discomfort.

Hikers may suffer a loss of performance of up to 30%, and experience flushing, low endurance, rapid heart rates, elevated body temperatures, and rapid onset of fatigue.

Symptoms of mild dehydration include thirst, decreased urine volume, abnormally dark urine, unexplained tiredness, irritability, headache, dry mouth, dizziness when standing due to ortho-static hypo-tension, and in some cases can cause insomnia.

The symptoms become increasingly severe with greater water loss. One’s heart and respiration rates begin to increase to compensate for decreased plasma volume and blood pressure, while body temperature may rise because of decreased sweating. Around 5% to 6% water loss, one may become groggy or sleepy, experience headaches or nausea, and may feel tingling in one’s limbs (paraesthesia). With 10% to 15% fluid loss, muscles may become spastic, skin may shrivel and wrinkle, vision may dim, urination will be greatly reduced and may become painful, and delirium may begin. Losses greater than 15% are usually fatal.

Treatment: The best treatment for minor dehydration is drinking water and stopping fluid loss. Water is preferable to other commercially-sold re-hydration fluids, as the balance of electrolytes they provide may not match the replacement requirements of the individual.

In some cases, eating of salted foods may have a positive impact on the person. However, eating salted foods should come with more intake of a clear liquid.

It is wise to slowly drink liquids when dehydrated.

When dehydrated, unnecessary sweating should be avoided, as it wastes water. If there is only dry food, it is better not to eat, as water is necessary for digestion.

For severe cases of dehydration where fainting, unconsciousness, or other severely inhibiting symptom is present, emergency attention is required. Fluids containing a proper balance of replacement electrolytes are given orally or intravenously with continuing assessment of electrolyte status; complete resolution is the norm in all but the most extreme cases.

Prevention: A useful rule of thumb for avoiding dehydration in hot or humid environments or during strenuous activity involves monitoring the frequency and character of urination. If one develops a full bladder at least every 3-5 hours and the urine is only lightly colored or colorless, chances are that dehydration is not occurring; if urine is deeply colored, or urination occurs only after many hours or not at all, water intake may not be adequate to maintain proper hydration.

During high physical activity such as hiking, water stops and water breaks are necessary to avoid dehydration.

If water is being lost through abnormal mechanisms such as vomiting or diarrhea, an imbalance can develop very quickly into a medical emergency. In fact, the main mechanisms through which diseases such as infantile diarrhea and cholera kill their victims are dehydration and loss of electrolytes.

WAD: Wilderness Acquired Diarrhea

Definition: Diarrhea from pathogens acquired in the wilderness is sometimes called wilderness-acquired diarrhea (WAD). Diarrhea acquired in the wilderness is typically a form of infectious diarrhea, itself classified as a type of secretory diarrhea. These are all considered forms of gastroenteritis. It is a much-discussed hazard among backpackers, hikers, campers and other outdoor recreationers who visit wilderness areas in temperate climates. Risk factors include drinking untreated surface water and insufficient washing of hands and food utensils, i.e. insufficient hygiene, which may result in person to person transmission of microbes that cause WAD.

Causes: Infectious diarrhea acquired in the wilderness is caused by various bacteria, viruses, parasites and protozoa. The most commonly reported are the protozoa Giardia and Cryptosporidium. Modes of acquiring infection from these causes are limited to fecal-oral transmission, and contaminated water and food. The major factor governing pathogen content of surface water is human and animal activity in the watershed.

Symptoms: The onset usually occurs within the first week of return from the field, but may also occur at any time while hiking.

Most cases begin abruptly and usually result in increased frequency, volume, and weight of stool. Typically, a hiker experiences at least four to five loose or watery bowel movements each day. Other commonly associated symptoms are nausea, vomiting, abdominal cramping, bloating, low fever, urgency, and malaise, and usually the appetite is affected. The condition is much more serious if there is blood or mucus in stools, abdominal pain, or high fever. Dehydration is a possibility. Life-threatening illness resulting from WAD is extremely rare but can occur in people with weakened immune systems.

Diagnosis: It may be difficult to associate a particular case of diarrhea with a recent wilderness trip of a few days because incubation of the disease may outlast the trip. Studies of trips that are much longer than the average incubation period, e.g. a week for Cryptosporidium and Giardia, are less susceptible to these errors since there is enough time for the diarrhea to occur during the trip. Other bacterial and viral agents have shorter incubation periods, although hepatitis may require weeks.

A suspected case of wilderness diarrhea may be assessed within the general context of intestinal complaints.

Treatment: WAD is typically self-limited, generally resolving without specific treatment. Oral re-hydration therapy with re-hydration salts is often beneficial to replace lost fluids and electrolytes. Clear, disinfected water or other liquids are routinely recommended.

Hikers who develop three or more loose stools in a 24-hour period — especially if associated with nausea, vomiting, abdominal cramps, fever, or blood in stools — should be treated by a doctor and may benefit from antibiotics, usually given for 3–5 days. Alternatively, a single dose azithromycin or levofloxacin may be prescribed. If diarrhea persists despite therapy, travelers should be evaluated and treated for possible parasitic infection.

There is no effective antibiotic against Cryptosporidium, which can be quite dangerous to patients with compromised immune systems.

Prevention: Since wilderness acquired diarrhea can be caused by insufficient hygiene, contaminated water, and (possibly) increased susceptibility from vitamin deficiency, prevention methods should address these causes.

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