Altitude sickness

Altitude sickness is a general term encompassing several disorders that occurhigh altitudes. High altitude is greater than 8,000 feet; medium altitude isbetween 5,000 and 8,000 feet; and extreme altitude is greater than 19,000 feet. There are groups of people who have lived at high altitudes for generations, and they are simply accustomed to living at such altitudes. However, people who are accustomed to lower altitudes are at risk of developing altitude sickness.

Most healthy individuals suffer altitude sickness at very high altitudes. About 20% of people ascending above 9,000 feet in one day will develop altitudesickness. Individuals with preexisting medical conditions--even a minor respiratory infection--may become sick at more moderate altitudes.

Altitude sickness occurs because the air contains less oxygen at higher altitudes. Therefore, there is a lower amount of oxygen for an individual to breathe. This is known as hypoxia. Furthermore, since there is less oxygen to inhale, less oxygen reaches the blood. This is known as hypoxemia. These two conditions are the major factors that form the basis for all the medical problemsassociated with altitude sickness.

Acute mountain sickness (AMS) is a mild form of altitude sickness that results from ascent to altitudes higher than 8,000 feet. Some individuals are affected at even lower altitudes. AMS tends to be most severe on the second or third day after reaching the high altitude, and it usually lessens after three to five days if the person remains at the same altitude. Symptoms include dizziness, headache, shortness of breath, nausea, vomiting, loss of appetite, andinsomnia.

High-altitude pulmonary edema (HAPE) is a life-threatening condition that afflicts a small percentage of those who suffer from AMS. In this condition, fluid leaks from blood vessels into the lung tissue. As this fluid accumulates within the lung tissue (pulmonary edema), the individual begins to become moreand more short of breath.

Typically, the individual with HAPE ascends quickly to a high altitude and almost immediately develops shortness of breath, rapid heart rate, cough productive of a large amount of sometimes bloody sputum, and rapid breathing. Without medical assistance, the patient goes into a coma and dies within hours.

High-altitude cerebral edema (HACE), the rarest and most severe form of altitude sickness, involves cerebral edema. The symptoms often begin with those ofAMS, but neurologic symptoms such as an altered level of consciousness, speech abnormalities, severe headache, loss of coordination, hallucinations, andeven seizures. Without medical intervention, death results.

Diagnosing altitude sickness relies on the individual's symptoms during travel to higher altitudes. Mild AMS requires no treatment other than an aspirin or ibuprofen for headache, and avoidance of further ascent. Narcotics should be avoided because they may blunt the respiratory response. Oxygen may also beused to alleviate symptoms of mild AMS.

As for HAPE and HACE, the most important course of action is to descend to alower altitude as soon as possible. Even a 1,000-2,000-foot descent can improve symptoms. If descent is not possible, oxygen therapy should be started. Additionally, dexamethasone (a steroid) has been suggested in order to reduce cerebral edema.

The prognosis for mild AMS is good, if appropriate measures are taken. As forHAPE and HACE, the prognosis depends upon the rapidity and distance of descent and medical intervention.

To prevent altitude sickness, a person should spend at least one night at anintermediate altitude before going to higher elevations. In general, climbersshould take at least two days to go from sea level to 8,000 feet. After reaching that point, healthy climbers should allow one day for each additional 2,000 feet, and one day of rest should be taken every two or three days. Shouldmild symptoms begin to surface, further ascent should be delayed.

Attention to diet can also help prevent altitude sickness. Water loss is a problem at higher altitudes, so climbers should drink ample water and avoid alcohol and large amounts of salt. Eating frequent small, high-carbohydrate snacks, such as fruits and starchy foods, can help.

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