This is a simple useful test to perform if AMS is suspected. If someone fails this test, it means start descending, not ascending no matter what. When he checked her oxygen level in the blood with a small handy instrument called the Pulse oximeter, the oxygen level was fright-fully low. This fact together with the noises in the lungs told the doctor she had fluid in the lungs, another important organ besides the brain affected by mountain sickness. Another key to avoiding AMS is a rational ascent that gives your body time to acclimatize.
People acclimatize at different rates, so no absolute statements are possible.
Another very important factor is to avoid dehydration. These drugs hinder your breathing and dehydrate you. We do not recommend acetazolamide as a prophylactic medication. Most people who have a reasonable ascent schedule will not need it, and in addition to some common minor but unpleasant side effects it carries the risk of any of the severe side effects that may occur with sulfonamides. We do support its use under certain limited conditions.