Hypobaric Hypoxia

Hypobaric hypoxia is a condition where the body is deprived of a sufficient supply of oxygen from the air to supply for body tissues whether in quantity or molecular concentration. Hypoxic hypoxia affects the body’s ability to transfer oxygen from the lungs to the bloodstream. Oxygen is the main component required to maintain our body functions because it is involved in the oxidation of complex chemical food-stuff to produce energy for our other biological processes that happen inside our body. Hypoxic hypoxia therefore does not mean that erythrocytes are not enough to carry oxygen around from the alveoli of the lungs to the body tissues but simply the oxygen molecule that is to be carried is insufficient. This condition is particularly more likely to happen when a person ascends to a higher altitude. Hypoxia can lead to a loss of cognition, which can be detrimental, particularly for pilots who have to make important decisions that affect the safety of all passengers and crewmembers onboard. A total absence of oxygen in the human body is called anoxia. Hypobaric Hypoxia is the most commonly experienced form of hypoxia in flight and therefore is the main focus here on. Other forms of Hypoxia include the Anaemic hypoxia, Ischaemic hypoxia and Histotoxic hypoxia.


Both air pressure and air density decrease as altitude increases. When an aeroplane climbs the density of the air reduces therefore causing a lack of oxygen being transferred from the lungs to the bloodstream. When this occurs not enough oxygen is reaching the brain, as a consequence the body is not able to function efficiently or normally because of a lack of oxygen reaching the brain that requires a great deal of oxygen supply to kick-start its normal function to control and initiate other body functions. Moreover in flight, hypoxic hypoxia is generally worsened by the following causes:
*Ascending to an higher altitude without a supplementary supply of oxygen
*Failure of designed passenger breathing equipments to aid in supplying oxygen concentration adequately
*Pressure cabin decompresses as the aircraft climbs to an even higher altitude.

General Information

Hypoxia generally tends to affect most people above 10,000ft, people who are between 25 and 50 who are healthy and active do generally have a higher resilience. Above this height supplementary oxygen is needed, most aircraft will be pressurized to around 5,000ft in order to prevent hypoxia. In people who are stressed, ill or fatigued, symptoms can often be noticed as low at 8,000ft. If an aircraft ascends rapidly to 50,000ft, the partial pressure of oxygen is even further decreased to a level of 10% of the lung's partial pressure of oxygen at mean sea level. This scenario will allow only 15 seconds at the most for the pilot to respond before they get unconscious or at least 4 minutes for a human being to die. Susceptibility is further increased by anything which reduces the oxygen level to the brain and even drugs that slow down brain activity. It is also more calamitous at night as the pilots also this condition also makes vision poor especially for pilots flying VFR. Hypobaric hypoxia is an interest for aviators and researchers since its neurological effects impair the mental performance of pilots and others on board. Interestingly enough, this condition has been known to have the ability to increase the risks for a pilot to make mistakes on cognitive and psychomotor tasks and even impairing the senses of our body. Moreover, this condition has heights in which the body has its oxygen content declined and if human reach these heights, no matter their expertise or how they have mastered a skill, they are prone to be mistaken in the judgements they make because the body's brain is impaired and that is where decisions are made.

Signs and Symptoms

Initial symptoms are often hardly noticeable to the sufferer at first, generally they will have a feeling of euphoria. The signs and symptoms vary from person to person. However, below is a list of the most common symptoms of hypoxia:

  • Fatigue
  • Lack of cognition
  • Lethargic
  • Headaches
  • State of euphoria
  • Shortness of breath
  • Loss of Consciousness
  • Pins and needles
  • High pulse rate
  • Deterioration of vision
  • Blue lips and fingernails
  • Moodiness
  • Drowsiness


As a precaution one should consider the following in mind before flying so that the chances of suffering from hypobaric hypoxia are controlled to a minimal.

  • Drink plenty of fluids prior to flying, and remain well hydrated.
  • Avoid drinking alcohol 24 hours prior to flying, as alcohol has a tendency to dehydrate the body.
  • Gain plenty of sleep prior to flying in order to avoid symptoms of fatigue.
  • Cabin Pressurisation
  • Physically and mentally fit
  • NO Smoking
  • Avoid using sedatives


Despite the efforts of promoting awareness and enhancing the quality of aircraft designs and pilot trainings to eliminate the occurrence of Hypobaric Hypoxia, it is still experienced and to be safe it is a must for one to know what to do during the Time of Useful Consciousness that is the time that one can actively do something before he gets unconscious. The following are suggested actions:

  • The primary treatment for hypoxia is the administration of supplementary oxygen, most commonly through the means of an oxygen mask.
  • Reducing altitude (For pilots in particular)

Time of Useful Consciousness

The following is a list of the altitude and the corresponding length of time that one has to act to combat the effects of Hypobaric Hypoxia.

Altitude Time of Useful Consciousness with Minimal Activity
18,000ft approx. 30 minutes
22,000ft approx. 10 minutes
25,000ft approx. 3 minutes
30,000ft approx. 75 seconds
35,000ft approx. 45 seconds
40,000ft approx. 15 seconds


Example of the effects Hypoxia

The following video shows how hypoxia can affect the human body at altitude.

(video embedded from YouTube on 28 August 2009)

Want to know more?

Wikipedia - Hypoxia (medical)
This page in Wikipedia offers more detailed information about the occurrence.


  1. Asshauer, H. (2009). Hypoxia: An Invisible Enemy. Retrieved August 28, 2009 from http://www.airbus.com/store/mm_repository/pdf/att00007996/media_object_file_FAST38_Hypoxia.pdf.
  2. Wikipedia (2009). Hypoxia (medical). Retrieved August 28, 2009 from http://en.wikipedia.org/wiki/Hypoxia_%28medical%29
  3. YouTube (2007). Controlled Hypoxia in Altitude Chamber. Retrieved August 28, 2009 from http://www.youtube.com/watch?v=qLQMupV3DLk.
  4. Robson, D. (2008). Human being pilot: human factors for aviation professionals. Cheltenham, Victoria; Aviation Theory Centre.
  5. Harding, R. M. (1999). Hypoxia and Hyperventilation. In J. Ernsting,. A. Nicholson., & D. Rainford (Eds)., Aviation Medicine (3rd ed., pp. 43-58). Woburn, MA: Butterworth-Heinemann.
  6. Gradwell, D. P. (1999). Prevention of Hypoxia. In J. Ernsting,. A. Nicholson., & D. Rainford (Eds)., Aviation Medicine (3rd ed., pp. 59-76). Woburn, MA: Butterworth-Heinemann.

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