High Altitude Sickness Atmospheric pressure is a gauge of how many oxygen molecules are available per given volume, say a breath. While the percentage of oxygen in the air remains constant, lower atmospheric pressure at higher altitudes means fewer oxygen molecules are available with each breath. The atmospheric pressure at the summit of Mount Everest is about a third that at sea level. Physiological studies have shown that it is only sufficient to support a human being at rest.

Trekkers take a break. Credit: KOA

In the higher elevations, a condition to be wary of is the Acute Mountain Sickness (AMS). Commonly known as altitude sickness, the condition is caused by climbing too quickly to a higher altitude. According to experienced trekkers, at high altitudes halts for acclimatization should be taken at every increase of 2000 to 4000 ft altitude. High altitude sickness can become fatal if it is not attended promptly and carefully. If ignored, serious problems of evacuation of the casualty may arise, and in the worst cases the person affected may die on the mountain.

The symptoms of AMS include vomiting, headaches that persist even after taking the usual medicines usual medicines, breathlessness, and exhaustion that does not lessen with rest. These are just warning symptoms that should not be ignored, to avoid a serious illness. The treatment is simply rest at a lower altitude. Further ascent should not be attempted until the symptoms go away completely.

If ignored, conditions may worsen to Severe AMS. An affected person's balance and muscle coordination is affected. Other classic signs include breathlessness with almost any activity. The person also becomes angry, irritable or incomprehensible. Under these conditions, a person should not attempt to go to a higher altitude at all, unless there are options for an easy and rapid descent should symptoms recur.

On the life-threatening end of the spectrum is a severe swelling known as High Altitude Cerebral Edema (HACE). HACE has been known to occur as low as 10,000 ft above sea level. The higher the elevation, the more severe HACE can become. Symptoms include ataxia or loss of balance and muscle coordination. The person's mental functioning decreases rapidly and severe headaches, nausea and vomiting are experienced. Hallucinations or stroke-like symptoms follow, and speech becomes slurred. Coma and death may rapidly follow unless the person can immediately be evacuated to a lower altitude.

High Altitude Pulmonary (O)Edema (HAPE, or HAPO) is a condition that rarely occurs below 8,000 ft altitude. High altitude trekkers occasionally experience flu-like symptoms at high altitudes which go away at lower heights. This is actually HAPE, in which a build up of fluids occurs in the lungs. This leads to a feeling of severe fatigue. Pulmonary edema is a result of greatly increased blood flow through the lungs, as the body tries to obtain the maximum amount of oxygen from the air. The heart increases the flow by increasing the pressure, causing leakage from the blood vessels into the air sacs of the lungs. Pulmonary edema usually takes a few days to develop. Symptoms include extreme difficulty in breathing, a very rapid heart beat rate and breathing rate, and extreme exhaustion with any exertion. In severe cases, death can occur in minutes unless the person can be evacuated immediately to lower altitudes.

According to Dr Eric Weiss, when trekkers first started going to the Everest base camp, 1 in 50 died. Nowadays, thanks to awareness of high altitude problems, that figure is 1 in about 10-50,000.