Hypoxia, hyperventilation & carbon monoxide
Hypoxia is too little oxygen reaching the tissues. It is insidious: it brings euphoria, impaired judgement and coordination, tunnel vision, and blue lips and nails (cyanosis), and the pilot usually does not notice it happening. Night vision is one of the first things to go, so use oxygen from the ground up at night (TC AIM AIR 3.5); it can begin to suffer around 5,000 ft (PHAK, not the TC AIM). Higher up, your time of useful consciousness shrinks fast.
Four types, by where the oxygen chain breaks:
| Type | The break |
|---|---|
| Hypoxic | Low oxygen pressure in thin air (the altitude one). |
| Anaemic | The blood cannot carry oxygen (carbon monoxide, anaemia). |
| Stagnant | Poor circulation (high G, extreme cold). |
| Histotoxic | The cells cannot use the oxygen (alcohol, drugs). |
Hyperventilation is over-breathing from stress, which blows off too much carbon dioxide. It gives tingling, dizziness and light-headedness, easily mistaken for hypoxia. Fix: slow the breathing rate. If unsure at altitude, treat for hypoxia as well.
Carbon monoxide is anaemic hypoxia: exhaust leaking through the cabin heater. Signs are headache and drowsiness. Action: shut off the heater, open fresh-air vents, use 100% oxygen, land.
Trap: confusing hyperventilation (slow your breathing) with hypoxia, and thinking cherry-red skin (a carbon-monoxide sign) means hypoxia when oxygen-starved tissue actually turns blue.
Note: the cyanosis skin sign (blue lips and nails) is grounded in the FAA Pilot's Handbook (FAA-H-8083-25), a free public-domain text; it is universal and matches TC Human Factors (TP 12863). The four types, carbon monoxide (with its cherry-red sign) and hyperventilation stay cited to TC AIM AIR 3.2.
References
- TC AIM AIR 3.2
- TC AIM AIR 3.5
- FAA Pilot's Handbook of Aeronautical Knowledge (FAA-H-8083-25)