Hypoxia

Hypoxia

Hypoxia means "reduced oxygen". During flight not enough oxygen getting to your brain can become extremely problematic. It can reduce mental function and if prolonged can lead to death. There are many things that can cause hypoxia and there are four types:

Hypoxic Hypoxia

Hypoxic hypoxia is the result of not enough oxygen reaching your lungs. When this occurs, your lungs cannot absorb enough oxygen (because there is insufficient available) and not enough oxygen reaches your blood. There are many things that can cause this, but some examples include:

• A blocked airway (choking)
  • When an airway gets blocked you're unable to breath properly and oxygen does not reach your lungs.
• Altitude
  • When climbing in altitude, the pressure of the atmosphere decreases. As this pressure decreases, there is not enough partial pressure for your lungs to absorb enough oxygen and therefore not enough oxygen makes it into your blood. (don't confuse this with hypemic hypoxia) The percentage of oxygen remains the same regardless of altitude however, the number of molecules in a given space reduces as you climb in altitude. This can lead to hypoxic hypoxia

Hypemic Hypoxia

Hypemic hypoxia is the result of insufficient oxygen in the blood stream and therefore insufficient oxygen reaching your cells and tissue. Some examples include:

• Carbon monoxide poisoning
  • Carbon monoxide (CO) is extremely efficient (about 200 times more efficient than oxygen) at attaching to the hemoglobin in your blood. When exposed to large concentrations of CO your blood absorbs large quantities of it and there is little to no room left for oxygen to get into your blood stream. This results in your cells not receiving enough oxygen.
• Insufficient blood
  • If you have insufficient blood available in your body (a good example may be from donating blood) then your blood stream will be unable to absorb enough oxygen (because there is not enough blood) for all of your cells.

Stagnant Hypoxia

Stagnant hypoxia occurs when your blood is not flowing and therefore your cells are unable to get fresh oxygen. Some examples include:

• Sitting on a limb in a way that compresses the blood vessel and restricts blood flow
• Pulling multiple Gs in an airplane. When pulling Gs your body is experiencing many times its weight and your heart is unable to pump your blood effectively.
• Cold temperatures can also affect the constriction of your blood vessels which can decrease your blood supply to your extremities

Histotoxic Hypoxia

Histotoxic hypoxia is the inability of your cells/tissues to efficiently use the oxygen that is available. This is typically caused by the use of drugs and/or alcohol. Enough oxygen is available and is being transported to the cells but they're unable to use it effectively. 

Symptoms of Hypoxia

The brain and many other vital organs can become quickly impaired by oxygen starvation. Generally, the first symptoms experienced are euphoria and a feeling of carelessness. The longer oxygen starvation continues the worse symptoms can get. Generally basic motor functions can become difficult and hand eye coordination becomes quickly impaired. The symptoms of hypoxia can vary from person to person but the most common symptoms include:

• Headache
• Dizziness
• Nausea
• Impaired Judgement
• Cyanosis (fingertips and lips turn blue)
• Drowsiness
• Tingling in extremities
• Numbness
• Euphoria
• Visual Impairment
• Decreased response to stimuli and an increased reaction time

"As hypoxia worsens, the field of vision begins to narrow and instrument interpretation can become difficult. Even with all these symptoms, the effects of hypoxia can cause a pilot to have a false sense of security and be deceived into believing everything is normal." (FAA-H-8083-25C Pilot's Handbook of Aeronautical Knowledge)

Treatment of Hypoxia

Some treatments include, flying at a lower altitude and/or using supplemental oxygen. If your airplane has cabin heat that uses the exhaust to heat the air, you can disable cabin heat and open the windows (if able). The best way to prevent hypoxia is to use supplemental oxygen when needed.

Useful Consciousness

Useful consciousness is the amount of time you have before brain function is significantly impacted by oxygen deprivation. As altitude increases the time for useful consciousness decreases. [Figure 1]

Figure 1 Time of useful consciousness (Pilots Handbook of Aeronautical Knowledge)