Hypoxia is a state of oxygen deficiency in the body, and it has dangerous effects. The brain of a person with hypoxia does not function normally. This can result in the a hypoxic person thinking and feeling they are normal, when they are, in fact, very hypoxic. The result is a person with poor judgment, degraded senses, and poor decision making abilities continuing to fly, instead of taking action to remedy their hypoxia. For these reasons, it is important to understand the symptoms of hypoxia, and how to best avoid becoming hypoxic in the first place.

Hypoxia can take on many different appearances, depending on the individual. One person might become dizzy and tired, while another might begin to feel euphoric and indestructible. Common symptoms of hypoxia include:

  • Decreased reaction time
  • Impaired judgment
  • Tingling fingers and toes
  • Cyanosis (blueing of the lips and fingernails due to low oxygen content in the blood)
  • Visual impairments, usually diminished peripheral vision and poor color vision
  • Lightheaded feeling or dizziness
  • Euphoria
  • Headache
  • Drowsiness

Many of these symptoms, such as reaction time and impaired judgment are very difficult for a person with hypoxia to detect. Cyanosis may be hard to detect as well, since hypoxia degrades color vision significantly. Also, a person with hypoxia is usually unaware of their degraded color vision. It is also difficult to determine red from blue at night under red lighting.

Normally, a person in good health is at risk of becoming hypoxic at altitudes above 10,000 feet during the daytime, and altitudes above 5,000 feet at night. However, hypoxia can occur at lower altitudes, especially if things like poor diet, illness, smoking, or health problems are a factor. Even stress and fatigue make a person hypoxic. Just being tired makes a normal person slightly hypoxic on the ground, under normal oxygen pressure.

Types of Hypoxia:

Hypoxic (Altitude) Hypoxia

As the name implies, altitude hypoxia usually occurs as a result of reduced air pressures encountered at altitude. The higher the airplane is flown, the less the air pressure. Our bodies rely on pressure to press the oxygen through our lungs and into our blood stream. As pressure decreases, the blood has a harder and harder time absorbing oxygen from the lungs.

The air at altitude is comprised of the same portion of oxygen as the air at ground level, about 22%. However, without pressure, that oxygen is unavailable for use. In fact, even if a person breaths 100% pure oxygen, they will still become hypoxic at altitudes above 25,000 feet.

Altitude hypoxia occurs because there is a lack of oxygen available to the lungs.

Hypemic Hypoxia

Hypemic hypoxia results when the blood is unable to carry the oxygen normally. For example, the carbon monoxide present in engine exhaust causes hypemic hypoxia by bonding to the blood in such a way that the blood becomes less capable of carrying oxygen.

In this case, the lungs may have plenty of oxygen available, but the blood can't carry that oxygen from the lungs. Another example of hypemic hypoxia is massive bleeding. The reduced volume of blood is not able to carry the oxygen from the lungs and distribute it throughout the body normally.

Stagnant Hypoxia

Stagnant hypoxia results from stagnant blood. In the case of stagnant hypoxia, there is oxygen available in the lungs, and the blood is capable of carrying that oxygen normally. However, the blood is not moving adequately to deliver that oxygen throughout the body. For example, heart problems such as a heart attack or heart palpitations cause hypoxia.

Histotoxic Hypoxia

Histotoxic hypoxia is caused by a toxic substance preventing the cells of the body from metabolizing oxygen normally. In the case of histotoxic hypoxia, oxygen is available to the lungs, being carried normally by the blood, and being distributed normally by the blood. However, the cells in the tissues of the body are unable to use the oxygen. For example, histotoxic hypoxia is the result of the consumption of alcohol. Because the blood is well oxygenated, a person with histotoxic hypoxia will not exhibit cyanosis.

Reducing the Risk

The risk of hypoxia can be lessened by flying with proper rest, being in good health, not smoking, and flying at the appropriate altitude. Shorter flights also lessen exposure time to lower oxygen pressures. Perhaps the pilot might elect to breath supplemental oxygen to help prevent the occurrence of hypoxia.

During the flight, it is important to remain aware of how subtle the symptoms of hypoxia can be. For most people, if you begin to question whether you are hypoxic, you're hypoxic.

If there is question as to whether hypoxia exists, use supplemental oxygen if available. Hypoxia usually goes away within a minute or two after the use of supplemental oxygen is initiated. The other option is to descend into thicker air below, respecting terrain, obstructions, and airspace restrictions. In any case, be extra conservative if hypoxia is suspected.

Supplemental Oxygen

The pilot must use oxygen anytime the airplane is flown above an altitude of 12,500 for more than 30 minutes. Pilots must by on oxygen anytime the airplane is flown above 14,000 feet MSL.

If the aircraft is flown above 15,000 feet MSL, then all passengers must be provided with oxygen. Only the pilots are required to use it.

If you intend to fly a pressurized aircraft, make sure to learn the oxygen requirements for these airplanes.