What is the most common cause of in-flight hypoxia?

The most common cause of in-flight hypoxia is related to the decreased partial pressure of oxygen at high altitudes. As an aircraft ascends to higher altitudes, the atmospheric pressure decreases, which in turn reduces the partial pressure of oxygen available in the environment. While the percentage of oxygen in the atmosphere remains approximately the same at various altitudes (about 21%), the lower overall pressure means that fewer oxygen molecules are available for absorption into the bloodstream.

This is particularly significant because human physiology relies on a certain partial pressure of oxygen in the air to facilitate effective oxygen transfer from the lungs to the blood. When flying at altitude, especially above 10,000 feet, pilots and passengers may experience symptoms of hypoxia if supplemental oxygen is not utilized or if they have pre-existing health conditions that exacerbate the effects of reduced oxygen levels.

Inadequate cabin pressurization can contribute to hypoxia as well, but the primary factor affecting most situations of in-flight hypoxia is the natural reduction of oxygen availability due to altitude. Factors such as respiratory illness and sedation from medications may impair oxygen saturation but are not as prevalent as the altitude-induced decrease in oxygen pressure experienced during flights.