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Hypoxia

Hypoxia is a state of oxygen deficiency in the body sufficient to impair functions of the brain and other organs.

Hypoxia is caused by the reduction of barometric pressure at altitude (the concentration of oxygen actually stays relatively constant).

Symptoms​

  • Cyanosis (blue fingernails and lips)
  • Headache
  • Decreased response to stimuli and increased reaction time
  • Impaired judgment
  • Euphoria
  • Visual impairment
  • Drowsiness
  • Lightheaded or dizzy sensation
  • Tingling in fingers and toes
  • Numbness

Onset​

  • Hypoxia can affect many pilots as low as 5000' MSL at night
  • In the day, typical pilots are not greatly impaired below 12,000'
  • At cabin pressure altitudes above 15,000 feet:
    • The periphery field of vision grays until only a central point remains vision remains (tunnel vision)
    • A blue coloration (cyanosis) of the fingernails and lips develops
  • The ability to take corrective action is lost in 20 to 30 minutes at 18,000 feet
  • It is lost in 5 to 12 minutes at 20,000 feet, followed soon thereafter by unconsciousness.

For optimum protection, pilots are encouraged to use supplemental oxygen above 10,000 feet during the day, and above 5,000 feet at night.

Types​

  • Hypoxic hypoxia: Caused by the reduction in partial pressure of oxygen at high altitude
  • Hypemic hypoxia: Caused by the blood not being able to take up and transport a sufficient amount of oxygen
  • Stagnant hypoxia: Caused by a lack of circulation of oxygenated blood in the body
  • Histotoxic hypoxia: Caused by the inability of the cells to effectively use oxygen