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High Altitude Sickness Information

Altitude:Kilimanjaro and Meru

Altitude effects people differently and there are no specific factors such as age, sex, or physical condition that correlate with one’s susceptibility to altitude sickness. Most people can hike to 2,438 meters (8,000 feet) with minimal effect. If this is your first trip at altitude, it is important to be extremely cautious when hiking either Meru or Kilimanjaro.

Altitude is commonly given three rankings – high, very high, and extremely high. The lower and upper boundaries of these ranks are shown in the table below.


  • 2,500 to 4,000 meters
  • 8,000 to 13,000 feet
  • Adaptation sufficient

Very High

  • 4,000 to 5,500 meters
  • 13,000 to 18,000 feet
  • Adaptation not sufficient; acclimatization necessary

Extremely High

  • Over 5,500 meters
  • Over 18,000 feet
  • Acclimatization not possible; deterioration

The summit of Kilimanjaro, 5895 meters (19,340 feet), falls in the extremely high category and proper precautions should be taken to mitigate the risks of high altitude hiking. The highest camps of Kilimanjaro, Barafu and Kibo, fall in the very high altitude category and hikers could experience severe signs of altitude sickness at these camps. Although Mount Meru is often viewed as an acclimatization hike for Kilimanjaro, its peak, at 4,566 meters (14,990 feet), falls in the very high altitude category and hikers can also experience severe altitude sickness.

What is Altitude Sickness

Symptoms associated with altitude sickness result from the body’s inability to adjust to lower levels of oxygen in the blood. At sea level, the concentration of oxygen is about 21% and the barometric pressure averages 760 mmHg. As altitude increases, oxygen concentration remains the same but the number of oxygen molecules per breath is reduced due to lower barometric pressure. At 3,658 meters (12,000 feet), barometric pressure decreases to 483 mmHg, resulting in roughly 40% fewer oxygen molecules per breath. In order to increase oxygen levels in the blood, your body responds by breathing faster. Although oxygen levels increase, sea level concentrations cannot be reached. The body must adjust to having less oxygen. This adjustment is called acclimatization. At elevations above 5,500 meters, acclimatization is not possible and the body begins to deteriorate.


The main cause of altitude sickness is going too high too fast. Given enough time, your body will adapt to the decrease in oxygen at a specific altitude. This process is known as acclimatization and generally takes one to three days at any given altitude.

Upon climbing to a higher elevation, the body must readjust to the new altitude again over a period of one to three days.

In order to cope with decreased oxygen levels, the body reacts in the following ways:

  • Respiration frequency and depth increases
  • Pressure in pulmonary arteries is increased, “forcing” blood into portions of the lung that are normally not used during sea level breathing.
  • Additional red blood cells are produced to carry oxygen?•Enzymes are produced to facilitate the transfer of oxygen from hemoglobin to body tissues.

It is imperative that hikers remain aware of Acute Mountain Sickness symptoms during Kilimanjaro and Meru trips, and that they communicate with the guide regularly regarding their condition. It is very important to rest and not ascend further if experiencing severe symptoms of AMS.

Cheyne-Stokes Respiration

Above 3,000 meters (9,842 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 for a few seconds before shallow breathing begins again. This can disturb sleeping patterns, exhausting the climber. This type of breathing is not considered abnormal at high altitudes. Diamox is helpful in relieving this periodic breathing.

Acute Mountain Sickness (AMS)

Acute Mountain Sickness is common at high altitudes and 75% of people experience some symptoms over 3,000 meters (9,842 feet). The severity of AMS depends on several factors including rate of ascent, elevation, and individual susceptibility. Symptoms usually begin between 12 and 24 hours after reaching altitude and decrease in severity by the third day.

Mild AMS symptoms include:

headache, nausea and dizziness, loss of appetite, fatigue, shortness of breath, and inability to sleep. As long as the symptoms are mild, hikers can continue to climb at a moderate rate. All symptoms of AMS should be communicated to the head guide and progress reports should be given daily.

Moderate AMS symptoms include:

Severe headache, nausea and vomiting, increased weakness and fatigue, shortness of breath, and decreased coordination.

Although the hiker may be able to continue walking on their own while experiencing moderate symptoms of AMS, normal activity becomes more and more difficult as the hiker gains altitude. At this stage, only medicine and descent can reverse the symptoms of AMS. Even a minor descent of only 300 meters will result in a significant improvement. All symptoms of moderate AMS should be communicated to the guide at which point the guide will make a decision whether or not to evacuate.

Severe AMS symptoms include:

Increased shortness of breath, loss of ability to walk, decreasing mental awareness, and fluid buildup in lungs.

Severe AMS can only be treated by immediate descent to lower altitudes.

Other Severe Altitude-Related Illnesses

Two other severe forms of altitude sickness may result from failure to descend to lower altitudes. These include High Altitude Pulmonary Edema (HAPE) and High Altitude Cerebral Edema (HACE). Although these happen less frequently, they usually result from fast ascents among people who are not properly acclimatized.

High Altitude Pulmonary Edema (HAPE)

HAPE results from fluid buildup in the lungs and can prevent effective oxygen exchange. Symptoms of HAPE include: shortness of breath even at rest; fatigue and weakness; feeling of impending suffocation or drowning; grunting or gurgling sounds when breathing; persistent cough which brings up white, watery, or frothy fluid; confusion and irrational behavior. In cases of HAPE, immediate descent is necessary. Patients should be evacuated to a medical facility for follow-up treatment.

 High Altitude Cerebral Edema (HACE)

HACE is the result of swelling of brain tissue from fluid leakage. Symptoms include the following: headache; loss of coordination (ataxia); weakness; decreasing levels of consciousness including, disorientation, loss of memory, hallucinations, blindness, and coma. HACE generally occurs after a week or more at high altitude. Severe instances can lead to death if not treated quickly and immediate descent is a necessary life-saving measure. Follow-up care must be sought at a medical facility following HACE.

Preventing Altitude Sickness

There are two ways to prevent altitude-related illness: proper acclimatization and preventative medicines. These recommendations are written specifically for climbing Mounts Meru and Kilimanjaro in Tanzania and may not be applicable to other high mountains.

  • Tell guide your AMS symptoms and keep him as well as the other group members informed of your progress.
  • Climb high and sleep low. It is recommended that you acclimate during the day by climbing to high elevations and then descending to sleep.
  • If you begin to show symptoms of moderate altitude illness, don’t go higher until symptoms decrease.
  • If symptoms become severe, descend.
  • Stay properly hydrated. Acclimatization is often accompanied by fluid loss, so you need to drink lots of fluids to remain properly hydrated (at least 4-6 liters per day). Urine should be clear.
  • Don’t over-exert yourself at altitude. Light activity during the day is better than sleeping because respiration decreases during sleep, exacerbating the symptoms.
  • Avoid tobacco and alcohol and other depressant drugs including barbiturates, tranquilizers and sleeping pills. Depressants further decrease the rate of respiration during sleep resulting in a worsening of the symptoms.
  • Eat a high calorie diet of which 70% is carbohydrates.


Diamox (Acetazolamide) is a drug that allows you to breathe faster so that you metabolize more oxygen. The recommended dose is between 125 mg and 250 mg twice daily starting one to two days before the trek and continuing for three days once the highest altitude is reached. Contact your physician for more information and a prescription. Since Diamox is a sulfonamide drug, people who are allergic to sulfa drugs should not take Diamox. Diamox has also been known to cause severe allergic reactions to people with no previous history of Diamox or sulfa allergies.

Ibuprofen relieves altitude induced headache.


Duma Explorer is not responsible for any negative side effects of high altitude climbing including side effects resulting from medications used. Duma Explorer has merely included information on AMS and related medicines to inform you and help you prepare for a Kilimanjaro or Meru climb. It is your responsibility to ensure that you are in proper condition to climb Kilimanjaro and Meru. There are certain inherent risks in adventure travel that apply to any Duma Explorer activity. These include, but are not limited to, risks of high altitude climbing, walking safaris, hiking and dangers from animals. The client assumes all risks in relation to these trips.


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