Oxygen and Respiration — Page 51, Lesson 78

I want to walk you through a specific type of hypoxia that we touched on earlier — Anaemic Hypoxia. This is a critical concept for you as a pilot because it affects your blood's ability to carry oxygen, and it can be caused by things you might not immediately associate with altitude. Anaemic Hypoxia is caused by the blood's inability to carry oxygen. The two main causes are a medical condition called anaemia, which we discussed in Chapter 2, and carbon monoxide poisoning. Both reduce the oxygen-carrying capacity of your blood. Now, let's focus on a very practical cause: smoking. When you smoke, you inhale carbon monoxide. Here's the key mechanism: the haemoglobin in your red blood cells has a much greater affinity — a much stronger chemical attraction — to carbon monoxide than it does to oxygen. So, the carbon monoxide binds to the haemoglobin instead of oxygen, and that reduces the amount of haemoglobin available to transport oxygen around your body. The result is that a heavy smoker will have 8% to 10% of their haemoglobin tied up as carboxyhaemoglobin — that's the compound formed when carbon monoxide binds to haemoglobin. Because of this, a regular smoker will start to suffer from hypoxia at an altitude approximately 4,000 to 5,000 feet lower than a non-smoker would. So if a non-smoker starts feeling hypoxic at 10,000 feet, a heavy smoker might feel those same effects at 5,000 or 6,000 feet. I cannot overstate the importance of aircrew being able to recognize hypoxia. It is of particular danger to inexperienced aircrew who may not recognize the onset of the initial symptoms. You need to know what it feels like for you, because the early signs can be subtle. Let's move on to the Treatment of Hypoxia. The key is knowledge of the signs and symptoms, and early identification of the problem. That allows you to carry out the correct drills before anyone is placed in jeopardy. But it's vital that these drills are well learned and easily accomplished — you don't want to be fumbling with a checklist when your brain is starved of oxygen. The two principal actions are: 1. Provide oxygen — immediately. 2. Descend to a level where atmospheric oxygen is present in sufficient quantities to meet the body's needs, or to the Minimum Safe Altitude (MSA), whichever is the higher. So you're either going down to where the air is thick enough to sustain you, or to a safe altitude for terrain, whichever is higher. Aircrew must familiarize themselves with the appropriate oxygen drills for the aircraft they are flying before venturing above an altitude at which hypoxia can occur — and that threshold is above 10,000 feet. Finally, let's look at Prevention of Hypoxia. Some factors that predispose you to hypoxia are unavoidable risks of flying, but others can be reduced by good personal habits and forethought. Here are the key pointers: - When anticipating flying above 10,000 feet, ensure that a serviceable supplementary supply of oxygen is available and that you know the correct method of use. - Ensure that passengers are correctly briefed on oxygen use. - If you smoke — stop. - Fly only if you are 100% fit and you are not taking any medication or drugs. - Ensure that cabin heaters are thoroughly checked and serviceable. If used, ensure that fresh air is also brought into the cabin — this is important because a faulty cabin heater can be a source of carbon monoxide. So to summarise: Anaemic Hypoxia is about the blood's inability to carry oxygen, smoking makes it worse by creating carboxyhaemoglobin, treatment is oxygen and descent, and prevention is about fitness, equipment, and avoiding carbon monoxide sources.