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Hypoxia is essentially a human condition that results from a fall in partial pressure of oxygen, which causes the lack of adequate oxygen supply in body tissues. Hypoxia must not be confused with hypoxemia, which is basically a condition of low arterial oxygen supply. Moreover, anoxia is quite different from hypoxia - a complete deprivation of oxygen supply.

Hypoxia is, therefore, a result of ascension in high altitude. Historically, hypoxia was a concept realized by balloonists Jacques Montgolfier in the 17th century. Various symptoms come as a consequence of hypoxia and majorly regarding the impairment of memory and muscles. In addition, within the aviation industry hypoxia leads to numerous other physiological effects that affect passengers and flight crew. In the current paper, the focus is placed on hypoxia in the aviation industry.

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How does Hypoxia Happen During a Flight?

Breathable air comprises of approximately 20.95% of oxygen. By taking in oxygen the stores of energy in the form of Adenosine Triphosphate (ATP) in the body cells get replenished. The brain, despite constituting a small portion of the body, consumes 25% of oxygen and, hence, requires a constant supply of it. According to the federal aviation administration, the higher one flies, the less the air in the sky. Indeed, hypoxia is a progressive condition that is not easily detected as one slowly lapses into incompetence, while remaining at euphoric faith in one’s own abilities. It is at such high altitudes that supplemental oxygen becomes a necessary component, especially at heights of above 12500 feet MSL. If proper measures are not laid out, there is a high probability for air crash. For instance, the Cessna T182 of Ludlow California serves as a proper example. In this particular flight, the pilot was flying at 14,800 feet MSL after flying for about 40 minutes and without using any supplemental oxygen. It was then that the pilot became hypoxic, as evidenced by meandering flight path recorded by the air traffic controller. The final report of the National Transport Safety Board named the cause of the accident to be the in-flight impairment of the pilot due to hypoxia, as he operated without supplemental oxygen hence, causing him to lose control.

Consequences of Different Types of Hypoxia in Aviation

Hypoxic hypoxia is experienced by the pilots when they fly at altitude in an aircraft that is unpressurized. When altitude increases, oxygen molecules in the ambient air get apart and exert less pressure. The pressure of oxygen in the air decreases when pilots reach certain altitude. Additionally, there is the lower pressure of oxygen at that level, therefore, human lungs are not be able to transfer oxygen from the air to the blood. Hypemic hypoxia occurs when the blood is not able to carry enough oxygen. It may be caused by nitrites, hemoglobin abnormalities, hemorrhage or anemia. Likewise, stagnant hypoxia happens at the circulatory level. When there is any compromise in the blood flow, there will be no enough oxygen to get into the body tissues. When the blood flow is decreased, the heart will fail to pump the blood effectively. The latter kind of hypoxia occurs when a body is exposed to cold temperature, resulting in low blood flow intensity.

Lastly, historic hypoxia occurs at the cell level when the cells that require oxygen is impaired and thus cannot use. In aviation, it means that even with enough amounts oxygen, the cells are not able to get that oxygen. Generally, hypoxia leads to lapses in coordination, memory, judgment and signs masked by a well-being sense. For instance, the VFR was departing from Longmont at 4.57 PM for Las Vegas, 10 minutes before sunset. The conditions of the meteorology prevailed for the flight, and so the pilot flew for over 2 hours above 12,500 feet, for almost two hours above 14,000 feet and nearly 45 minutes above 16000 feet. The aircraft was unpressurized and the supplemental oxygen systems were non-functional. Another mistake is that the crew was not equipped with portable oxygen. Besides, the pilot, while flying 14,000 feet, was subjected to numerous corrections from the ATC especially after reporting that she flew over Montrose in Colorado, but was informed by the controller that she was over Telluride. Hypoxia also causes altitude sicknesses, resulting in fatal complications. When it gets worse, the pilot and the passengers feel skin tingling and also become dizzy. One may also experience strong headache, the heart races, skin under the fingernail and the lips start turning blue, one's vision field narrows.

Preventing Hypoxia

There are several ways of preventing hypoxia. The first assumes increasing barometric pressure but to reach a minimal level but in a way that oxygen concentration sufficiently prevents hypoxia. The method in question is known as cabin pressurization. The dissimilarity between the inner and outer pressure is in the incoming and outgoing airflow. The technique in cabin pressurization is basically to maintain barometric pressure (PBc) at a higher scale than that of the corresponding flight level (PBz). The approach is used along with the oxygen monitoring and systems which if well used, should ensure hypoxia is never experienced. As a part of the system, complex equipment is employed to assists in carrying out oxygen control in the cabin. For instance, there is built-in oxygen, portable oxygen, pulse oximeter and carbon monoxide detector.

Another key preventive measure is the use of supplemental oxygen and more specifically is the final approach to overcome impairment of nocturnal visions that is encountered from 8,000 feet. It is also applied in the case of other emergencies that involve failure of pressurization and in the case of fumes or smoke. According to Federal Aviation Regulations, the use of oxygen devices is described as a function of altitude. The key point is that supplemental oxygen is ideal for pilots and is mandated without condition. Furthermore, FAR 121 outlines that oxygen must be availed for at least ten percent of the passengers within a range of FL80-FL120 though excluding situations when the aircraft maintains the altitude for less than 30 minutes.

Determining Factors in Response to Hypoxia

The most dangerous thing about hypoxia is that it is practically impossible to understand when hypoxic reactions are about to begin. Consequently, the reactions to hypoxia differ among people and even within a particular person depending on the health, diet and body chemistry. In essence, some responses are characteristically dependent on the pilot's control, while others are caused by the environmental condition of the flight. First, the absolute altitude is an essential determining factor of the severity of hypoxia. As a matter of fact, there is an increased risk of hypoxia at rising altitudes and a drop in partial pressure of oxygen. Second, acclimatization is a major determining factor for the response to hypoxia. Such an aspect has allowed the Peruvians to be able to live in The Andes which is 17,000 feet. They, having adapted high altitude areas, can, therefore, manage to go through higher altitude flights as compared to other ordinary people. Third, the cabin temperature has an effect on an individual’s tolerance as well as one’s response to hypoxia. Extreme cold or hot temperature usually causes the body to utilize a lot of energy in the attempt to maintain body temperature within some the optimal limits. The high body activity causes a decline in a pilot’s tolerance for hypoxia.

Finally, other self-imposed factors vary among pilots and their susceptibility to oxygen deficiency. Essentially, it influences susceptibility to hypoxia and by avoiding  different aspects, a pilot will come under better control. These factors include the use of alcohol, exposure to carbon monoxide and excess fatigue. Compromise on any of these factors can have an impact on the logic judgment of the pilot even for issues that are quite simple. It is for such reasons that the pilot of flight VFR (PA-28R) made numerous errors in preflight planning which when integrated with hypoxic altitudes became the result of air crash near La Sal, Utah. For example, the pilot filed wrong information regarding the cruising altitude, speed of wind and fuel hours onboard. Really, the aircraft could not do more than five hours even without the wind effect and not eight as reported. Besides, the service ceiling for the aircraft is 15,000 feet and not 15,500 feet. Therefore, with the effects of the non-logic judgment of a pilot along with the effects of hypoxia, the end result was a crash.


At high altitudes, the lack of oxygen poses the greatest threat and leads to hypoxia. The hypoxia condition is by nature a grim deceiver, whereby it gives a person certain level of confidence that he or she is doing well. The ability of the body to adapt to hypoxia is usually constrained when the onset is fast. For such reason, the flight crew ought to be adequately informed about the causing factors as well as consequences resulting from hypoxia in flight. Recognizing, preventing and treatment of hypoxia condition demand the understanding of various pathophysiological components that cause hypoxia, symptoms, and prevention. Naturally, it is a duty of all the stakeholders in the aviation industry to ensure hypoxia does not cause any deaths.

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