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Understanding Hypoxia: Like a Breath of Fresh Air

By: The CTS Team   •  

Even if you don't regularly fly at high altitudes, knowing how to recognize and treat hypoxia remains a vital skill.

It only takes one unwitting adventure a bit higher than intended to throw a pilot a curveball in terms of understanding how to physically handle high altitudes. The symptoms of hypoxia can be deceptive, with many of them causing pilots to feel as though nothing is wrong at all, rather than being able to detect a problem. This swift, subtle onset can spell trouble for crews who have not been trained to detect the symptoms in themselves or others. Thus, dedicated training in identifying and reacting appropriately to hypoxia is recommended for all pilots, even those who normally remain below 10,000 ft.

Hypoxia is defined as a lack of sufficient oxygen in the body's blood, tissue, or cells to continue normal functions. This could occur as a result of not enough oxygen being present in the air, deficiencies in the circulatory system transporting that oxygen, or cell difficulty in absorbing the oxygen. Because flight often results in strains on the body or unusual environmental conditions, pilots are especially susceptible to all four types of hypoxia.

Types of Hypoxia

Hypoxia is classified by which bodily system is primarily affected. Although all four types generally carry the same symptoms and effects, awareness of their distinct causes can help you avoid all of them.

Hypoxic hypoxia is the most common type of hypoxia for pilots. At high altitudes, oxygen content in air remains the same, but the molecules are further apart and thus exert less pressure. As a result, when you breathe in air, the decreased pressure makes it more difficult for the lungs to transfer oxygen to the blood. Hypoxic hypoxia is usually anticipated and combated by pressurized cabins or oxygen mask requirements, but situations of slow decompression, system malfunctions, or simple lack of awareness at altitudes where 100% oxygen is recommended but not required can result in hypoxic hypoxia.

Hypemic hypoxia occurs when the blood is unable to carry oxygen as efficiently as it should. Even if the oxygen supply is adequate, hypoxia will still occur. This condition is uncommon in aviation, but may happen due to a medical condition such as anemia, or if carbon monoxide is inhaled due to a system malfunction or other event.

Stagnant hypoxia also involves the blood, occurring when blood flow is insufficient to carry oxygen where it needs to go. Some medical conditions could cause this, but pilots are more likely to experience this if they regularly perform aerial acrobatics, as G-forces could result in blood pooling.

Histotoxic hypoxia is caused when cell absorption of oxygen cannot occur due to the presence of alcohol or narcotics. This is but one of the many reasons to avoid alcohol consumption for a significant period of time before a flight.

Signs and Symptoms

Hypoxia's symptoms are nearly identical in anyone afflicted by it, though the symptoms may not always present in the same order for everyone. Many of the symptoms are so subtle that the hypoxic person may not notice they are suffering from it until it is too late. It is recommended that those who regularly fly above 10,000 ft. gain some experience in a hypobaric or altitude chamber during their training. By experiencing hypoxia's symptoms in a safe,controlled environment, they will be better equipped to recognize it when it happens.

The symptoms of hypoxia include:

  • Reduced night vision; though not practical for day flying, this is often the first symptom experienced and can be a good initial indicator that hypoxia is setting in
  • Breathlessness
  • Fatigue
  • A feeling of "fuzziness" when thinking
  • Difficulty performing simple mental tasks, such as math
  • Difficulty recalling something that has just occurred or information one has just learned
  • A sense of euphoria
  • Blue tinge to the fingers or lips
  • Headache
  • Unconsciousness

While some of these symptoms might seem noticeable enough, most people do not immediately suspect a serious problem when a headache or bout of yawning begins. Coupled with the sense of euphoria and fuzzy thinking, victims of hypoxia may instead feel that nothing is wrong at all. Pilots flying at high altitudes should be especially self-aware to detect any of these symptoms, even when flying in a pressurized cabin or with oxygen. Those who have lived much of their lives at lower altitudes, smokers, those experiencing stress, and those who are not physically fit will be more susceptible to hypoxia. Hypoxia's likelihood is also increased at higher ambient temperatures.

Treatment and Preventions

The difficulty in combating hypoxia largely lies in recognizing it quickly. Once known, the solutions are not complicated. Immediately upon recognizing either hypoxia or a system malfunction that will inevitably lead to hypoxia (such as decompression), descend to an altitude where oxygen will not be required--below 10,000 ft. Have the affected persons use supplemental oxygen, and encourage them to intentionally take slower, deliberate breaths. Perform a thorough check of related systems to either determine the cause of the hypoxia, or ensure you have the support to descend safely.

In general, it is best to limit your time above 10,000 ft to less than an hour, even less if you're above 12,000 ft. Even if you feel you don't need it, don your oxygen mask when above 10,000 feet during the day, or above 5,000 feet at night. Of course, comply with all oxygen requirements set forth in the CFRs, or stricter requirements put in place by your operation.

Finally, be sure to keep yourself in good physical condition. Although the regulations specify avoiding alcohol within eight hours of a flight, taking a more conservative approach is best, as alcohol consumption can make you susceptible to hypoxia for hours after you no longer feel the effects. Avoid smoking, be aware of stress levels and endeavor to reduce them, and above all, remain in close communication with your co-pilot. By remaining aware of one another's mental condition at all times, you can more easily detect hypoxia in both yourself and the other pilot, allowing for a swifter reaction.

Knowing the signs and reacting appropriately can keep your encounters with hypoxia short, unremarkable, or even non-existent.

Related CTS training:

  • Physiology and First Aid
  • Physiological Aspects of Flight

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