Edema and Related Medical Conditions

Comprehensive information on edema, swelling, treatment and medical conditions that can cause edema. For all articles, please click on "Archives"

Saturday, December 17, 2005

High altitude cerebral edema

Acute mountain sickness
Alternative names Return to top

High altitude cerebral edema; Altitude anoxia; Altitude sickness; Mountain sickness; High altitude pulmonary edema

Return to top

Acute mountain sickness is an illness that can affect mountain climbers, hikers, skiers, or travelers who ascend too rapidly to high altitude (typically above 8,000 feet or 2,400 meters). This is especially for persons who normally reside at or near sea level.

Causes, incidence, and risk factors Return to top

Reduced atmospheric pressure and a lower concentration of oxygen at high altitude are the causes of this illness. It affects the nervous system, lungs, muscles, and heart. Symptoms can range from mild to life-threatening.

In most cases the symptoms are mild, but in severe cases fluid collects in the lungs (pulmonary edema) causing extreme shortness of breath and further decreasing oxygenation. Swelling may also occur in the brain (cerebral edema), causing confusion, coma, and, if untreated, death.
The likelihood and severity of altitude illness is greater with increasing rate of ascent, higher altitude attained, and higher levels of exertion.

Approximately 20% of people will develop mild symptoms at altitudes between 6,300 to 9,700 feet, but pulmonary and cerebral edema are extremely rare at these heights. However, above 14,000 feet, a majority of people will experience at least mild symptoms, while approximately 10% and 1.5%, respectively, of un-acclimatized people staying at this altitude will develop pulmonary or cerebral edema.

Symptoms Return to top

Symptoms generally associated with mild to moderate altitude illness include:
Difficulty sleeping
Loss of appetite
Nausea or vomiting
Dizziness or light-headedness
Rapid pulse (heart rate)
Shortness of breath with exertion

Symptoms generally associated with more severe altitude illness include:

Shortness of breath at rest
Chest tightness or congestion
Bluish discoloration of the skin
Coughing up blood
Inability to walk in a straight line, or to walk at all
Decreased consciousness or withdrawal from social interaction
Gray or pale complexion (cerebral edema)

Signs and tests Return to top

Listening to the chest with a stethoscope (auscultation) reveals crackles in the lung fields in patients with pulmonary edema.
chest X-ray may be performed.

Treatment Return to top

The mainstay of treatment for all forms of altitude illness is to descend to lower altitude as rapidly and safely as possible. Supplemental oxygen should also be administered, if available.
Hospitalization may be required for severe illness.

Acetazolamide (Diamox) may be used to stimulate breathing, speed acclimatization, and diminish the milder symptoms of acute mountain sickness. Do not consume alcoholic beverages while taking Diamox, and drink sufficient fluids since Diamox increases urination.
Pulmonary edema is treated with oxygen, nifedipine (a high-blood pressure medication also effective for this disorder), and in severe cases, mechanical ventilation.

For cerebral edema, administration of the steroid drug dexamethasone (Decadron) may be helpful.

Expectations (prognosis) Return to top

Most cases are mild, and symptoms improve promptly with a return to lower altitude. Severe cases may result in death due to respiratory distress or brain swelling (cerebral edema).
In remote locations, emergency evacuation may not be possible, or treatment may be delayed.

These conditions could adversely affect the outcome.

Complications Return to top

Pulmonary edema
High altitude cerebral edema (brain swelling)

Calling your health care provider Return to top

Call your health care provider if symptoms of acute mountain sickness develop, even if symptoms resolved when returning to a lower altitude.

Call the local emergency number (such as 9-1-1) or seek emergency medical assistance if severe difficulty breathing develops, if consciousness is decreased, if coughing up blood, or if other severe symptoms are present. If unable to contact emergency help, descend immediately, as rapidly as is safely possible.

Prevention Return to top

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 2,000 feet (600 meters) above 8,000 feet (2,400 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 9,840 feet (3,000 meters) should carry an oxygen supply sufficient for several days.

Acetazolamide (Diamox) helps to speed acclimatization and reduce 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.

Those susceptible to anemia (particularly women) should consult a doctor regarding an iron supplement to correct the condition before traveling in high altitudes. Anemic persons have a reduced red blood cell count, and therefore, a lower amount of oxygen carried in the blood.

Drink sufficient 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.

Update Date: 1/29/2004
Updated by: Cherlin Johnson, M.D., Department of Emergency Medicine, University of Southern California, Los Angeles, CA. Review provided by VeriMed Healthcare Network.

Medline Plus


Acute Mountain Sickness (AMS)

AMS is very common at high altitude. At over 3,000 metres (10,000 feet) 75% of people will have mild symptoms. The occurrence of AMS is dependent upon the elevation, the rate of ascent, and individual susceptibility. Many people will experience mild AMS during the acclimatisation process. The symptoms usually start 12 to 24 hours after arrival at altitude and begin to decrease in severity around the third day.

The symptoms of Mild AMS include:

Nausea & Dizziness
Loss of appetite
Shortness of breath
Disturbed sleep
General feeling of malaise


The pleasures of trekking in the world's highest mountain ranges cannot be overstated. Neither can the dangers. Altitude sickness can occur in some people as low as 8,000 feet, but serious symptoms do not usually occur until over 12,000 feet. Even then it is not the height that is important, rather the speed in which you ascended to that altitude.Acute mountain sickness (AMS) is actually more common in fit young men because they are more likely to attempt a rapid ascent by racing up the mountain like some indestructible super hero! As a general rule, it is far safer (and more enjoyable) to avoid altitude sickness by planning a sensible itinerary that allows for gradual acclimatisation to altitude as you ascend, (you can race back down as fast as you like!).

2,500 to 4,000 metres
8,000 to 13,000 feet
Very High
4,000 to 5,500 metres
13,000 to 18,000 feet
Extremely High
over 5,500metres
over 18,000feet

What is High Altitude?

It is difficult to determine who may be affected by altitude sickness since there are no specific factors such as age, sex, or physical condition that correlate with susceptibility. Some people get it and some people don't because some people are more susceptible than others.Most people can ascend to 2,500 metres (8,000 feet) with little or no effect. If you have been at that altitude before with no problem, you can probably return to that altitude without problems as long as you are properly acclimatised. If you haven't been to high altitude before, you should exercise caution when doing so.

The Causes of Altitude Sickness

The percentage of oxygen in the atmosphere at sea level is about 21% and the barometric pressure is around 760 mmHg. As altitude increases, the percentage remains the same but the number of oxygen molecules per breath is reduced. At 3,600 metres (12,000 feet) the barometric pressure is only about 480 mmHg, so there are roughly 40% fewer oxygen molecules per breath so the body must adjust to having less oxygen.

In addition, high altitude and lower air pressure causes fluid to leak from the capillaries in both the lungs and the brain which can lead to fluid build-up. Continuing on to higher altitude without proper acclimatisation can lead to the potentially serious, even life-threatening altitude sickness.


The main cause of altitude sickness is going too high too quickly. Given enough time, your body will adapt to the decrease in oxygen at a specific altitude. This process is known as acclimatisation and generally takes one to three days at any given altitude, e.g. if you climb to 3,000 metres and spend several days at that altitude, your body will acclimatise to 3,000 metres. If you then climb to 5,000 metres your body has to acclimatise once again.

Several changes take place in the body which enable it to cope with decreased oxygen:

The depth of respiration increases.
The body produces more red blood cells to carry oxygen.
Pressure in pulmonary capillaries is increased, "forcing" blood into parts of the lung which are not normally used when breathing at sea level.
The body produces more of a particular enzyme that causes the release of oxygen from haemoglobin to the body tissues.
Cheyne-Stokes Respirations

Above 3,000 metres (10,000 feet) most people experience a periodic breathing during sleep known as Cheyne-Stokes Respirations. The pattern begins with a few shallow breaths and increases to deep sighing respirations then falls off rapidly even ceasing entirely for a few seconds and then the shallow breaths begin again. During the period when breathing stops the person often becomes restless and may wake with a sudden feeling of suffocation. This can disturb sleeping patterns, exhausting the climber. This type of breathing is not considered abnormal at high altitudes. Acetazolamide is helpful in relieving this periodic breathing.

Acute Mountain Sickness (AMS)

AMS is very common at high altitude. At over 3,000 metres (10,000 feet) 75% of people will have mild symptoms. The occurrence of AMS is dependent upon the elevation, the rate of ascent, and individual susceptibility. Many people will experience mild AMS during the acclimatisation process. The symptoms usually start 12 to 24 hours after arrival at altitude and begin to decrease in severity around the third day.

The symptoms of Mild AMS include:

Nausea & Dizziness
Loss of appetite
Shortness of breath
Disturbed sleep
General feeling of malaise

Symptoms tend to be worse at night and when respiratory drive is decreased. Mild AMS does not interfere with normal activity and symptoms generally subside within two to four days as the body acclimatises. As long as symptoms are mild, and only a nuisance, ascent can continue at a moderate rate. When hiking, it is essential that you communicate any symptoms of illness immediately to others on your trip.

Moderate AMS

The signs and symptoms of Moderate AMS include:

Severe headache that is not relieved by medication
Nausea and vomiting, increasing weakness and fatigue
Shortness of breath
Decreased co-ordination (ataxia).

Normal activity is difficult, although the person may still be able to walk on their own. At this stage, only advanced medications or descent can reverse the problem. Descending only 300 metres (1,000 feet) will result in some improvement, and twenty four hours at the lower altitude will result in a significant improvement. The person should remain at lower altitude until all the symptoms have subsided (up to 3 days). At this point, the person has become acclimatised to that altitude and can begin ascending again.

The best test for moderate AMS is to have the person walk a straight line heel to toe just like a sobriety test. A person with ataxia would be unable to walk a straight line. This is a clear indication that an immediate descent is required. It is important to get the person to descend before the ataxia reaches the point where they cannot walk on their own (which would necessitate a stretcher evacuation).

Severe AMS

Severe AMS results in an increase in the severity of the aforementioned symptoms including: Ÿ Shortness of breath at rest, Ÿ Inability to walk, Ÿ Decreasing mental status, Ÿ Fluid build-up in the lungs, Severe AMS requires immediate descent of around 600 metres (2,000 feet) to a lower altitude.

There are two serious conditions associated with severe altitude sickness; High Altitude Cerebral Oedema (HACO) and High Altitude Pulmonary Oedema (HAPO). Both of these happen less frequently, especially to those who are properly acclimatised. But, when they do occur, it is usually in people going too high too fast or going very high and staying there. In both cases the lack of oxygen results in leakage of fluid through the capillary walls into either the lungs or the brain.

High Altitude Pulmonary Oedema/Edema (HAPO)

HAPO results from fluid build up in the lungs. This fluid prevents effective oxygen exchange. As the condition becomes more severe, the level of oxygen in the bloodstream decreases, which leads to cyanosis, impaired cerebral function, and death.

Symptoms of HAPO include:

Shortness of breath at rest
Tightness in the chest, and a persistent cough bringing up white, watery, or frothy fluid
Marked fatigue and weakness
A feeling of impending suffocation at night
Confusion, and irrational behaviour

Confusion, and irrational behaviour are signs that insufficient oxygen is reaching the brain. One of the methods for testing yourself for HAPO is to check your recovery time after exertion. In cases of HAPO, immediate descent of around 600 metres (2,000 feet) is a necessary life-saving measure. Anyone suffering from HAPO must be evacuated to a medical facility for proper follow-up treatment.

High Altitude Cerebral Oedema/Edema (HACO)

HACO is the result of the swelling of brain tissue from fluid leakage.

Symptoms of HACO include:

Loss of co-ordination
Decreasing levels of consciousness
Loss of memory
Hallucinations & Psychotic behaviour

It generally occurs after a week or more at high altitude. Severe instances can lead to death if not treated quickly. Immediate descent of around 600 metres (2,000 feet) is a necessary lifesaving measure. There are some medications that may be used for treatment in the field, but these require proper training in their use.

Anyone suffering from HACO must be evacuated to a medical facility for follow-up treatment.

Prevention of Altitude Sickness

This involves proper acclimatisation and the possible use of medications.

If possible, don't fly or drive to high altitude. Start below 3,000 metres (10,000 feet) and walk up.

If you do fly or drive, do not overexert yourself or move higher for the first 24 hours.

If you go above 3,000 metres (10,000 feet), only increase your altitude by 300 metres (1,000 feet) per day, and for every 900 metres (3,000 feet) of elevation gained, take a rest day to acclimatise.

Climb high and sleep low! You can climb more than 300 metres (1,000 feet) in a day as long as you come back down and sleep at a lower altitude.

If you begin to show symptoms of moderate altitude sickness, don't go higher until symptoms decrease.

If symptoms increase, go down, down, down!

Keep in mind that different people will acclimatise at different rates. Make sure everyone in your party is properly acclimatised before going any higher.

Stay properly hydrated. Acclimatisation is often accompanied by fluid loss, so you need to drink lots of fluids to remain properly hydrated (at least four to six litres per day). Urine output should be copious and clear to pale yellow.

Take it easy and don't overexert yourself when you first get up to altitude. But, light activity during the day is better than sleeping because respiration decreases during sleep, exacerbating the symptoms.

Avoid tobacco, alcohol and other depressant drugs including, barbiturates, tranquillisers, sleeping pills and opiates such as dihydrocodeine. These further decrease the respiratory drive during sleep resulting in a worsening of symptoms.

Eat a high calorie diet while at altitude.

Remember: Acclimatisation is inhibited by overexertion, dehydration, and alcohol.

Preventative Medications

Acetazolamide (Diamox): This is the most tried and tested drug for altitude sickness prevention and treatment. Unlike dexamethasone (below) this drug does not mask the symptoms but actually treats the problem. It seems to works by increasing the amount of alkali (bicarbonate) excreted in the urine, making the blood more acidic. Acidifying the blood drives the ventilation, which is the cornerstone of acclimatisation.

For prevention, 125 to 250mg twice daily starting one or two days before and continuing for three days once the highest altitude is reached, is effective. Blood concentrations of acetazolamide peak between one to four hours after administration of the tablets.

Studies have shown that prophylactic administration of acetazolamide at a dose of 250mg every eight to twelve hours before and during rapid ascent to altitude results in fewer and/or less severe symptoms (such as headache, nausea, shortness of breath, dizziness, drowsiness, and fatigue) of acute mountain sickness (AMS). Pulmonary function is greater both in subjects with mild AMS and asymptomatic subjects. The treated climbers also had less difficulty in sleeping.

Gradual ascent is always desirable to try to avoid acute mountain sickness but if rapid ascent is undertaken and actazolamide is used, it should be noted that such use does not obviate the need for a prompt descent if severe forms of high altitude sickness occur, i.e. pulmonary oedema or Gradual ascent is desirable to try to avoid acute mountain sickness. If rapid ascent is undertaken and aceazolamide is used, it should be noted that such use does not obviate the need for prompt descent if severe forms of high altitude sickness occur, i.e. pulmonary or cerebral oedema.

Side effects of acetazolamide include: an uncomfortable tingling of the fingers, toes and face carbonated drinks tasting flat; excessive urination; and rarely, blurring of vision.

On most treks, gradual ascent is possible and prophylaxis tends to be discouraged. Certainly if trekkers do develop headache and nausea or the other symptoms of AMS, then treatment with acetazolamide is fine. The treatment dosage is 250 mg twice a day for about three days.

A trial course is recommended before going to a remote location where a severe allergic reaction could prove difficult to treat if it occurred.Dexamethasone (a steroid) is a drug that decreases brain and other swelling reversing the effects of AMS. The dose is typically 4 mg twice a day for a few days starting with the ascent. This prevents most of the symptoms of altitude illness from developing.

WARNING: Dexamethasone is a powerful drug and should be used with caution and only on the advice of a physician and should only be used to aid acclimatisation by sufficiently qualified persons or those with the necessary experience of its use.

For further information go to the Mountain Medicines page.

Treatment of AMS

The only cure for mountain sickness is either acclimatisation or descent.Symptoms of Mild AMS can be treated with pain killers for headache, acetazolamide and dexamethasone. These help to reduce the severity of the symptoms, but remember, reducing the symptoms is not curing the problem and could even exacerbate the problem by masking other symptoms.

Acetazolamide allows you to breathe faster so that you metabolise more oxygen, thereby minimising the symptoms caused by poor oxygenation which is especially helpful at night when the respiratory drive is decreased.

Dexamethasone: This powerful steroid drug can be life saving in people with HACO, and works by decreasing swelling and reducing the pressure in the skull. The dosage is 4 mg three times per day, and obvious improvement usually occurs within about six hours. This drug "buys time" especially at night when it may be problematic to descend. Descent should be carried out the next day. It is unwise to ascend while taking dexamethasone: unlike diamox this drug only masks the symptoms.

Dexamethasone can be highly effective: many people who are lethargic or even in coma will improve significantly after tablets or an injection, and may even be able to descend with assistance. Many pilgrims at the annual festival at Gosainkunda lake in Nepal suffer from HACO following a rapid rate of ascent, and respond remarkably well to dexamethasone. Mountain climbers also sometimes carry this drug to prevent or treat AMS. It needs to be used cautiously, however, because it can cause stomach irritation, euphoria or depression.It may be a good idea to pack this drug for a high altitude trek for emergency usage in the event of HACO In people allergic to sulpha drugs (and therefore unable to take diamox) dexamethasone can also be used for prevention: 4 mg twice a day for about three days may be sufficient.

Other Medicines used for treating Altitude Sickness include:

Ibuprofen which is effective in relieving altitude induced headache. (600mg three times a day).

Nifedipine: This drug is usually used to treat high blood pressure. It rapidly decreases pulmonary artery pressure and also seems able to decrease the narrowing in the pulmonary artery caused by low oxygen levels, thereby improving oxygen transfer. It can therefore be used to treat HAPO, though unfortunately its effectiveness is not anywhere as dramatic that of dexamethasone in HACO. The dosage is 20mg of long acting nifedipine, six to eight hourly.Nifedipine can cause a sudden lowering of blood pressure so the patient has to be warned to get up slowly from a sitting or reclining position. It has also been used in the same dosage to prevent HAPO in people with a past history of this disease.

Frusemide may clear the lungs of water in HAPO and reverse the suppression of urine brought on by altitude. However, Frusemide can also lead to collapse from low volume shock if the victim is already dehydrated. Treatment dosage is 120mg daily.

Breathing · 100% Oxygen also reduces the effects of altitude sickness.

The Gamow Bag

This clever invention has revolutionised field treatment of altitude sickness. The bag is composed of a sealed chamber with a pump. The casualty is placed inside the bag and it is inflated by pumping it full of air effectively increasing the concentration of oxygen and therefore simulating a descent to lower altitude

In as little as 10 minutes the bag can create an "atmosphere" that corresponds to that at 900 to 1,500 metres (3,000 to 5,000 feet) lower. After two hours in the bag, the person's body chemistry will have "reset" to the lower altitude. This acclimatisation lasts for up to 12 hours outside of the bag which should be enough time to get them down to a lower altitude and allow for further acclimatisation.

The bag and pump together weigh about 6.5 kilos (15 pounds) and are now carried on most major high altitude expeditions. Bags can be rented for short term treks or expeditions.

The Travel Doctor