For slower onset, which would be seen with altitude sickness, fatigue, headaches, and shortness of breath will be the first symptoms of a problem. Many people who are becoming hypoxic also feel nauseated and euphoric. When they become severely hypoxic or the hypoxia occurs very rapidly, seizures, coma, changes in consciousness levels, and death occur. By the time the issue is realized by others, there might not be an opportunity to help the person who has been experiencing the lack of oxygen without some type of permanent damage to the brain or other organs. Being aware of the symptoms of hypoxia that comes on slowly -- as it does when flying to a high altitude -- is very important because there is time to reverse the problems that start to occur. The earlier the lack of oxygen is noticed, the better the opportunity to descend to a lower altitude or receive supplemental oxygen to avoid hypoxia.

Altitudes and Onset

At sea level, a person's blood is oxygenated at or near 97%. When that same person goes to an altitude of 10,000 feet, the oxygen saturation in the blood drops to 90%. That is still enough for most normal life functions, although people in the medical field want to see a person's oxygen saturation point at or over 93%. At 14,500 feet (on the top of Pike's Peak, for example), the saturation is closer to 80%. That will cause the majority of people to have difficulty breathing, fatigue, nausea, and other symptoms that come along with altitude sickness. At 25,000 feet, oxygen saturation in the blood has dropped all the way to 55% and the person would lose consciousness. A pulse oximeter that clips on a finger is worn by many pilots today in order to see if they are becoming hypoxic.

The main altitude concerns are as follows:

5000 feet -- the retina of the eye will not get as much oxygen as it needs, and vision will be slightly compromised. This will be noticed most often in night vision. It is easier to misinterpret features on the ground, and maps and instruments in the cockpit can also be misread more easily. While most people can still fly safely at that altitude, it is important to be more careful than one would need to be at lower altitudes.

10,000 feet -- night vision is severely compromised, and this is the highest altitude at which pilots should trust their performance and instincts without supplemental oxygen. The minimum supply of oxygen is all that is being received at that point. Euphoria is common at that altitude, and after four hours or more there could be headaches and tingling that will also surface. Once a person flies over 10,000 feet in altitude, he or she will be severely disabled and will have dim vision and many other problems.


As can be seen, hypoxia is a very serious issue that can actually lead to death if not caught in time and taken seriously. Flying at a lower altitude or adding supplemental oxygen are the easiest ways to avoid or correct hypoxia. However, one of the biggest problems is that the person who is becoming hypoxic often does not realize the problem in its early stages. He or she may not notice the decrease in vision or the lapse in judgment. It may be assumed that the headache is just from being tired. It is…