Perhaps you’ve heard of hypoxia, as well as anoxia, but do you know what it is? Hypoxia is a deficiency of oxygen in the blood, whereas anoxia is the complete absence of oxygen in the blood.
It’s known that air is composed of 21% oxygen, but it’s important to consider that, as we ascend, pressure decreases, hence air particles are more spread out.
What does this mean? According to Dalton’s Law, the partial pressure of oxygen decreases, and with fewer oxygen particles entering our bodies, there will be a lower concentration of oxygen in the blood.
Continuing with the theme of oxyhaemoglobin, then, why might an episode of hypoxia occur during a flight?
It’s because the external pressure decreases, changing the amount of gases present in the lungs, resulting in less oxygen in them. And when does the pressure change? Exactly! It decreases when ascending and increases when descending.
It can also occur during cabin depressurisation, when the pressure outside the aircraft plays a crucial role in oxygen transfer.
Apart from being at high altitudes, as can happen during a flight, hypoxia can be caused by:
How can you identify hypoxia before it becomes anoxia? Symptoms of oxygen deficiency in the blood are:
Euphoria, a feeling of complete well-being, is a symptom to be particularly cautious of when discussing hypoxia, as it can be experienced above 10,000 feet, and if it occurs to a solo-flying pilot, it can be very dangerous.
Moreover, the level of hypoxia can be affected by the individual’s physical condition, the level of decompression, the altitude of the flight, and the affected individual’s own tolerance.
An important fact is that a regular smoker may begin to suffer from hypoxia at 6,000 feet, and smoking is considered one of the risk factors since carbon monoxide binds to haemoglobin and blocks the transfer of oxygen.
As you see, to work in the air, one must be healthy to avoid all risk factors. Thus, pilots must regularly be checked to be fit to fly, and how is this achieved? By passing the exam to obtain the Aviation Medical Certificate.
As mentioned before, partial pressure decreases with altitude, but from what altitude does this become significant?
Well, this depends on each person, their health state, and habits but generally, we can divide the body’s reaction to this decrease in oxygen into three stages:
This threshold is reached when the decrease in the amount of oxygen reaching the body starts to be noticeable, around 7,000 feet. Here we can observe how performing complex tasks becomes more difficult, and there’s a slight increase in heart rate and respiration. Additionally, night vision is also affected starting from 5,000 feet.
It occurs between 10,000 and 12,000 feet when blood oxygen saturation significantly decreases, and the body begins to activate defence mechanisms to avoid the effects of hypoxia.
When we reach this stage, the body struggles to perform tasks and maintain attention and alertness. From 12,000 feet we can suffer euphoria, drowsiness, dizziness, fatigue, and headache.
It occurs around 22,000 feet, and the most significant aspect is that blood oxygen saturation decreases to 65-60%, considering that the normal saturation at sea level is 95-100%.
This significant decrease triggers a rapid deterioration of our mental functioning with great confusion and dizziness, even potentially leading to loss of consciousness.
Prevention depends on the cause:
Aviation is a sector formed by professionals from all fields who combine all their knowledge to make aviation a safe and efficient mode of transport, plus both pilots and cabin crew are trained to recognise symptoms and know how to act in case it occurs.
