Hypoxia

Hypoxia is the lack of sufficient oxygen in the blood, tissues, and/or cells to maintain normal physiological function, which is particularly hazardous in the aviation environment.


Hypoxia

Introduction to Hypoxia

  • Hypoxia occurs when the tissues of the body do not receive enough oxygen, leading to incapacitating effects.
  • While most often associated with higher altitudes, there are several causes of hypoxia.
    • Depending on the cause, pilots experience various types of hypoxia.
  • Symptoms can be difficult to detect, especially when flying as a single-pilot, but left untreated, they can quickly turn deadly.
  • While easily treated, several factors can put a pilot at greater risk, necessitating hypoxia prevention and proper training as a first-line defense against hypoxia.
  • Further, oxygen requirements will help curb risk and serve as prevention.
  • Several case studies have shown that hypoxia can be deadly.

  • WARNING:
    All aeromedical topics are GENERALIZED.
    Always consult with a doctor or physician to understand your specific situation.

Hypoxia

Potential Causes of Hypoxia

  • Since hypoxia is the lack of sufficient oxygen in the body, hypoxia can result from several factors or a combination of those factors.
  • Equipment failure, such as leaky oxygen systems, inoperative oxygen masks, regulators, or depressurization, can result in conditions that lead to hypoxia.
  • Improper use of equipment, such as an improperly fitted mask or incorrect procedures, may result in hypoxia.
  • Environmental conditions such as underlying health conditions, behaviors, or environment can make the body increasingly susceptible to hypoxia.
  • Hypoxia may also be the result of certain flight conditions that restrict the flow of blood throughout the body.
  • Of course, simply spending too much time in a high-altitude environment can result in the body's hypoxia.
  • Hypoxia is a blanket term that encompasses various types that can be classified based on the factors that contribute to it.

Hypoxia

Types of Hypoxia

  • There are four types of hypoxia, based on the source:
    1. Hypoxic hypoxia.
    2. Hypemic hypoxia.
    3. Stagnant hypoxia.
    4. >Histotoxic hypoxia.

  • Hypoxic Hypoxia:

    • Also referred to as altitude hypoxia, hypoxic hypoxia is the lack of oxygen absorbed by the body due to atmospheric conditions.
    • As pressure altitude increases, the partial pressure of oxygen decreases along with blood oxygen saturation.
      • The significant decrease in pressure leads to the body's inability to absorb oxygen.
      • The oxygen concentration in the atmosphere remains consistent at all altitudes (about 21%), whereas pressure is reduced by 50% by 18,000' and 75% by 34,000'.
    • Hypoxic hypoxia can occur due to faulty equipment, malfunctions, or improper use.

  • Hypemic Hypoxia:

    • Hypemic hypoxia occurs when the blood is unable to carry a sufficient amount of oxygen to the body's cells.
    • Caused by anemia, disease, blood loss, deformed blood cells, or carbon monoxide (CO) poisoning, especially in smokers.
    • CO attaches itself to hemoglobin about 200 times more easily than oxygen.
    • After CO poisoning, it can take up to 24 hours to recover.
    • Donating blood results in a higher physiological altitude.

  • Stagnant Hypoxia:

    • Stagnant hypoxia occurs from oxygen deficiency in the body due to poor circulation of the blood.
    • Pulling excessive Gs or cold temperatures (which constrict blood vessels) may reduce blood flow to the extremities.
    • Stagnant hypoxia may cause hyperventilation.

  • Histotoxic Hypoxia:

    • Histotoxic hypoxia is the inability of the body to use oxygen.
    • Caused by alcohol and other drugs, such as narcotics and poisons.
  • Regardless of type, the symptoms of hypoxia remain consistent, requiring pilots to know what to look for to recognize the onset of hypoxia.

Hypoxia

Recognizing Hypoxia

  • Hypoxia Symptoms:

    • Because of wide individual variations in susceptibility to hypoxia, it is impossible to predict precisely when, where, or how hypoxia reactions will occur in each pilot.
    • As a general rule, however, flights below 10,000 feet MSL without the use of supplemental oxygen can be considered safe, though night vision is particularly critical, and impairment of sight can occur at lower altitudes - especially for heavy smokers.
    • The onset of hypoxia is insidious and progresses slowly, with symptoms including:
      • Euphoria.
      • Headache.
      • Increased response time.
      • Impaired judgment.
      • Drowsiness.
      • Dizziness.
      • Tingling in fingers and toes.
      • Numbness.
      • Blue fingernails and lips (cyanosis).
      • Limp muscles.
      • Confusion or foggy decision-making.

  • Debilitating Effects

    • Time of Useful Consciousness
      Time of Useful Consciousness
    • The effects of hypoxia are usually quite challenging to recognize, especially when they occur gradually. [Figure 1]
    • This onset (gradual or rapid) and altitude will have a direct effect on the Time of Useful Consciousness (TUC) and Effective Performance Time (EPT).
      • Time of Useful Consciousness: refers to the pilot's ability to remain conscious when exposed to high-pressure altitudes. [Figure 2]
        • Published times reference a rapid decompression event.
      • Effective Performance Time: refers to a pilot's ability to function, regardless of consciousness.
    • The effects appear following increasingly shorter periods of exposure to higher altitudes.
      • Pilot performance can seriously deteriorate within 15 minutes at 15,000 feet.
    • Although deterioration in night vision occurs at a cabin pressure altitude as low as 5,000', other significant effects of altitude hypoxia usually do not happen in the typical healthy pilot below 12,000'.
    • From 12,000 to 15,000' of altitude, judgment, memory, alertness, coordination, and ability to make calculations are impaired, and headache, drowsiness, dizziness, and either a sense of well-being (euphoria) or belligerence occur.
    • At cabin pressure altitudes above 15,000', the periphery of the visual field grays out to a point where only central vision remains (tunnel vision).
  • Once identified, pilots and passengers must take immediate action to address conditions that resulted in hypoxia, as well as the debilitating effects that resulted from the onset.
  • Time of Useful Consciousness
    Time of Useful Consciousness
  • 4 Stages of Hypoxia
    Four Stages of Hypoxia

Hypoxia

Immediate Action and Treatment of Hypoxia

  • If pilots or passengers suspect hypoxic conditions are present:
    • Inform your instructor/crew.
    • Descend to 10,000' or below.
    • Select the emergency position with the diluter lever (gang load).
    • Slow breathing rate by counting to four or five between breaths.
    • Check connections/equipment.
  • As always, avoiding the need to take immediate action to treat hypoxia starts with prevention.

Hypoxia

Hypoxia Prevention

  • Portable Fingertip Pulse Oximeter
    Amazon, Portable Fingertip Pulse Oximeter
  • Garmin D2 Delta PX, GPS Pilot Watch with Pulse Ox Sensor
    Amazon, Garmin Watch
  • For optimum protection, pilots are encouraged to use supplemental oxygen above 10,000' during the day and above 5,000' at night.
  • Pilots lose the ability to take corrective and protective action in 20 to 30 minutes at 18,000 feet and 5 to 12 minutes at 20,000 feet, followed soon after that by unconsciousness.
  • Pilots can best prevent hypoxia by heeding factors that reduce tolerance to increases in altitude (decreases in pressure) by enriching the inspired air with oxygen from an appropriate oxygen system and by maintaining a comfortable, safe cabin pressure altitude.
  • Portable Fingertip Pulse Oximeter
    Amazon, Portable Fingertip Pulse Oximeter
  • Several factors can lower the altitude at which significant effects of hypoxia occur.
    • Carbon monoxide inhaled in smoking or from exhaust fumes, lowered hemoglobin (anemia), and certain medications can reduce the oxygen-carrying capacity of the blood to the degree that the amount of oxygen provided to body tissues will already be equivalent to the oxygen supplied to the tissues when exposed to a cabin pressure altitude of several thousand feet.
    • Rate of pressure change.
      • Oxygen is given up through rapid decompression, causing loss of TUC by up to 50%.
    • Small amounts of alcohol and low doses of certain drugs, such as antihistamines, tranquilizers, sedatives, and analgesics, can, through their depressant action, render the brain much more susceptible to hypoxia.
    • Extreme heat and cold, fever, and anxiety increase the body's demand for oxygen and hence its susceptibility to hypoxia.
    • Duration of exposure.
    • Individual tolerances.
    • Physical activity.
      • If the pilot is physically fit and there are no fumes in the cockpit, the situation will probably never occur below 10,000'.
    • Self-imposed stress.
  • Garmin D2 Delta PX, GPS Pilot Watch with Pulse Ox Sensor
    Amazon, Garmin Watch
  • Avoid:
    • Smoking or exposure to exhaust fumes.
    • Medications.
    • Alcohol.
  • Oxygen Requirements:
    • Federal Aviation Regulations 91.211 requires that, at a minimum, the flight crew be provided with and use supplemental oxygen after 30 minutes of exposure to cabin pressure altitudes between 12,500 and 14,000' and immediately on exposure to cabin pressure altitudes above 14,000'.
    • Every occupant of the aircraft must be provided with supplemental oxygen at cabin pressure altitudes above 15,000'.
  • Resources are available for pilots to learn about the physiological effects and how hypoxia impacts them in particular.

Hypoxia

Hypoxia Training

  • Hypobaric Chamber
    Military Hypobaric Chamber
  • Since symptoms of hypoxia vary in an individual, experiencing and witnessing the effects of hypoxia during an altitude chamber "flight" significantly improves an individual's ability to recognize hypoxia. [Video 1]
  • The Federal Aviation Administration (FAA) provides this opportunity through aviation physiology training conducted at the FAA Civil Aeromedical Institute and many military facilities across the U.S. [Figure 5]
  • To attend the Physiological Training Program, contact the Civil Aeromedical Institute, Mike Monroney Aeronautical Center, Oklahoma City, OK.
    • Aerospace Medical Education Division, AAM-400, CAMI.
    • Mike Monroney Aeronautical Center, P.O. Box 25082.
    • Oklahoma City, OK 73125.
    • Telephone: (405) 954-6212.
  • Attendance at the Physiological Training Program requires an application form and a fee.
  • Particulars about location, fees, scheduling procedures, course content, individual requirements, etc., are contained in the Physiological Training Application, Form Number AC 3150-7, obtained by contacting the accident prevention specialist or the office forms manager in the nearest FAA office.
  • Hypobaric Chamber
    Military Hypobaric Chamber

Hypoxia

Hypoxia Case Studies

  • Lear Jet N47BA Flight Path After Becoming Hypoxic
    Lear Jet N47BA Flight Path After Becoming Hypoxic
  • The National Transportation Safety Board Identification: CEN12FA571:
    • The NTSB determines the probable cause(s) of this accident to be: The student pilot's impairment from alcohol, marijuana, and hypoxia, which adversely affected his ability to maintain control of the airplane.
  • The National Transportation Safety Board Identification: WPR12FA154:
    • The NTSB determines the probable cause(s) of this accident to be: The in-flight loss of control due to the pilot's impairment as a result of hypoxia. Contributing to the accident was the pilot's operation of the airplane above 12,500' without the aid of supplemental oxygen.
  • The National Transportation Safety Board Identification: CEN09LA527:
    • The NTSB determines the probable cause(s) of this accident to be: The in-flight loss of control due to the pilot's impairment as a result of hypoxia. Contributing to the accident was the pilot's decision to operate the unpressurized airplane at an altitude requiring supplemental oxygen without having any oxygen available.
  • The National Transportation Safety Board Identification: ERA09FA429:
    • The NTSB determines the probable cause(s) of this accident to be: The pilot's improper modification of the certified, on-board oxygen system, which resulted in incapacitation due to hypoxia, and the airplane's subsequent uncontrolled descent into terrain.
  • The National Transportation Safety Board Identification: DCA00MA005:
    • The NTSB determines the probable cause(s) of this accident as follows: Incapacitation of the flight crewmembers as a result of their failure to receive supplemental oxygen following a loss of cabin pressurization for undetermined reasons. [Figure 6]
  • Lear Jet N47BA Flight Path After Becoming Hypoxic
    Lear Jet N47BA Flight Path After Becoming Hypoxic

Hypoxia

Hypoxia Conclusion

  • Note that human performance is affected by pressure altitude.
    • Remember, there is no less oxygen at altitude than at sea level, but rather, the pressure of that air and the body's ability to absorb it changes.
    • Compliance, therefore, does not necessarily equate to safety.
  • The body's respiratory drive responds primarily to carbon dioxide and only weakly to oxygen levels, which makes the onset of hypoxia insidious.
  • Note the connection between supplemental oxygen requirements and hypoxia in case studies.
    • These rules are in place because others have died from it.
    • Recognize judgment will be impaired when hypoxic.
  • Although the regulations spell out specific oxygen requirements, a simple way to remember and a conservative practice is to use oxygen above 5,000' at night and 10,000' during the day.
  • A high-altitude endorsement is required if acting as pilot in command of a pressurized airplane with a service ceiling or maximum operating altitude above 25,000 feet.
  • Training may be made available through the FAA/Military to help pilots understand their body's response to hypoxia.
  • Rapid decompression is immediately recognizable and, therefore, easier to respond to, whereas a gradual decompression is harder to detect, increasing the risk of hypoxia with no clear warnings.
  • If you or your passengers experience signs or symptoms of hypoxia, report it! So that inspections on the aircraft can occur, and engineering inspections, if required, are initiated.
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Hypoxia

Hypoxia References