Hypoxia

From Pilots Almanac

Hypoxia is a state of oxygen deficiency in the body which is sufficient to cause an impairment of function. Hypoxia is caused by the reduction in partial pressure of oxygen, inadequate oxygen transport, or the inability of the tissues to use oxygen.

With increases in altitude, the total content of oxygen in a given volume of air decreases. Pilots may experience symptoms of hypoxia at altitudes as low as 10,000 msl. Above 14,000 feet, all flight crew members are required to be on supplimental oxygen.

The order of symptoms varies among individuals: increased breathing rate, headache, lightheadedness, dizziness, acute exhaustion, tingling or warm sensations, sweating, poor coordination, impaired judgment, tunnel vision, and euphoria. An immediate impairment in vision and judgment can occur resulting in unconsciousness and death if the proper amount of oxygen is not quickly restored. Smokers are more likely to experience increased effects of hypoxia.