Preventing Illness and Injury
Altitude Sickness

Cause

The official name is "acute mountain sickness". It is caused by thin air, i.e., the higher you go the less oxygen there is. The medical definition of high altitude starts with 8000' above sea level, where the atmospheric pressure is 75% of a standard (sea level) atmosphere of 1. At 14,000' it is 67 percent. At 18,000' it is 50 percent.

We will focus here on the 8000' - 14,000' range. (8000' is the approximate elevation of numerous trail heads on the east side of the Sierra; likewise in the Rockies and in the Northwest. 14,500' is the height of Mt. Whitney. 7000' is the elevation to which airplane cabins are pressurized. In the 8000' - 14,000' range the chief effects of altitude sickness are severe headaches, nausea and vertigo (dizziness).

You can move from sea level to 8000' with no minimal effects. This is because your body has the amazing capacity to adjust to decreasing oxygen. Your rate of breathing increases slightly and your kidneys re-balance an elevated pH level in your blood allowing your blood to carry more oxygen. If you continue higher; i.e., up to approximately 14,000' your body continues to compensate and re-balance. And in the course of about a week your body will have produced additional red blood cells to carry more oxygen. Ultimately you reach the limit of your body's ability to compensate (except over the much longer haul); for many this is in the 14,000' - 16,000' range.

Prevention

The capacity of a body to adapt to altitude and the speed with which it happens vary widely from person to person and also from time to time by the same person. These variations have no relationship to physical condition or strength. Yet everybody's ability to adapt is reduced by 1) dehydration, 2) alcohol or other depressants and 3) over-exertion. Therefore the best ways to prevent altitude sickness are:

If your trail head is at 5-8000' or above, spend the night before sleeping at the trailhead or similar elevation. Your body starts to adjust and is better able to further compensate when you go higher the next day.

Climb gradually and take it easy. This is especially important the first day.

Drink lots of water. This prevents dehydration and it makes you urinate a lot, which in turn increases your blood's oxygen carrying capacity (by decreasing the pH of your blood, which stimulates you to breathe faster in order to bring your pH back to normal).

Pay attention to what your body is telling you. If you start to feel nauseous or your head aches, it is telling you to stop until your body gets more oxygen circulating.

There is one other proven prevention: a prescription diuretic usually called Diamox. This should be reserved for 1) persons who from prior experience are particularly susceptible to mountain sickness, or 2) rapid assents of up to 14,000' that cannot be taken gradually. You end up urinating more, breathing more, and slightly hyperventilating. This increases your blood oxygen carrying capacity faster than your body would through natural adjustment. But there is a side effect. As you urinate you dump good electrolytes and water that you really need to keep, so these need to be replaced. Diamox is a prescription drug and should be used only after consultation with your doctor as to timing and dosage.