Oxygen Bar

October 26, 2011 by Bruce Landsberg

Last week we talked about the joys of operating in the flight levels and judging from the comments, the votes seemed to be overwhelmingly in favor of “bigger is better” or at least, easier. I recounted the wonders of the Cessna 441 at FL350 but there is one drawback to that magnificent machine.

The cabin altitude is about 11,000 feet and where slow-onset hypoxia should be considered. Some of the Foundation staff will claim that I’ve spent way too much time at altitude and am permanently hypoxic. (There are times I would agree.) However, this topic gets relatively little attention and even the FARs don’t even bring up the subject of oxygen impairment below 12,500 (5,000 at night). This blog is NOT about rapid decompression where the time of useful consciousness at those altitudes is measured in seconds.

A pulse oximeter is a wonderfully simple-to-use device that clips on a finger tip to instantly measure your oxygen saturation (sat)  and heart rate.  Ideally, at sea level, we’d all have 100% saturation and a pulse of about 60 – fat chance!  Many pilots may start in the low 90s. When your sat drops below 90%, oxygen deprivation is starting to take place. Thinking slows, and heart rate increases as the brain asks for more O2 to be pumped up.

As the sats fall, so does your ability and it can be quite insidious. After a few hours at 9,000-10,000, where many light non-pressurized aircraft fly, many of us will be hypoxic. A slight headache, fatigue, and the inability to process information as quickly as normal, are all symptoms but they vary person to person. But is it operationally significant? In more than few accident cases we see where an otherwise capable pilot made a poor decision that resulted in an accident. Why? One factor that is certainly present in some cases is slow onset hypoxia but you can’t measure O2 saturation on a corpse so the causes remain elusive and speculative.

On my flight back across the country in the C441 at FL350 last week (which we did non-stop in under 6 hours incidentally)  checking the sats was instructive. Both crew seats are equipped with quick-don masks and when my sat was dipping below 90% I’d take a few minutes to bring it back up to normal.  During these episodes it sounded like Darth Vader’s heavy breathing (Right here above planet earth but no Death Star in sight). Sitting in the back for a bit, without the benefit of oxygen,  resulted in sleepiness and my usual slight headache. The oxygen cleared it up. It’s bad enough when passengers are sleepy and a bit out of sorts. Their brains are starving for good air but for pilots this is critical.

The message is clear–if you spend much time above a cabin altitude of 8,000, your sats are going to come down—how quickly varies by individual. Healthy, fit, non-smokers will do better than others. Even if you’re not flying a turbocharged aircraft, you may want to think about  buying a pulse oximeter—they’re available for $30 – $100. After that little stocking stuffer, if the aircraft isn’t so equipped, get a portable oxygen system—your brain (and other body parts) will love it! The Air Safety Institute will be reviewing pilot misbehavior in the future due to oxygen deprivation.

Anyone have a good hypoxia story?

Bruce Landsberg
Senior Safety Advisor, Air Safety Institute

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  • NewsWordy

    The 12,500′ MSL is relatively arbitrary… many people need oxygen lower than that altitude to maintain 90% while I have flown at FL230 for over 3 hours maintaining 90% or better. This is about our INDIVIDUAL physiology. With or without supplemental oxygen, having the mask on doesn’t assure you will have sufficient sats… you NEED a pulse oxymeter to know. I have found myself using a cannula with sats down in the low 80s while in the high-teens because I was breathing shallow and not getting it into my lungs fully. Putting on a mask or cannula is only part of the story.

    Pulse oxymeters are a must have if flying where oxygen “might” be needed. When the FARs were written these devices were not generally available but they are now and the rule is about as useful as the 180 lb person (for W&B). I just bought a second unit for $30… my primary is one I wear on my wrist and can continuously monitor my sats. I’d strongly recommend that is SOP and meter your oxygen accordingly. You will learn what your body needs and eventually how to listen to it and know before you look at the pulse oximeter how you are doing.

  • M. Ross Shulmister

    “Recognizing and Dealing with Hypoxia”

    NewsWordy is right: It’s all about individually physiology. At 23 I flew a 172 at 15,500 from Minneapolis to DC without oxygen or symptoms. Now, and with a military aviation history, I KNOW how to recognize hypoxia, and at age 71 and at 15,500′ I WILL experience symptoms without supplemental O-2.

    Pilots who fly in the hypoxia zone SHOULD take a potentially life-saving course in an altitude chamber – my first “ride” I had no clue about the symptoms, and “woke up” protesting I didn’t need the mask yet. It was not until I looked down at what I was writing during the exercise that I realized just how unconscious I had become. We were then trained on the various hypoxia symptoms and how to recognize our own individual symptoms (which now I can do).

    Pilots who fly in the hypoxia zone should ALSO learn that there is a way to (at least temporarily) reduce hypoxia with a personal pressure-breathing exercise. Take a deep breath, and hold it while hunkering down (trying to exhale while still holding your breath), and repeat 8-10 times a minute. It will force more oxygen into the bloodstream – but it’s not something you can do for an extended period of time. It’s an emergency procedure to allow you to correct the oxygen problem, and it could buy you some desperately-needed minutes.

    In a hypoxic state, breathing faster not only doesn’t work, but also is likely to be dangerous. The human body has evolved in a way that natural breathing rate is attuned to the carbon dioxide in one’s blood, not the oxygen level. Breathing faster helps eliminate CO-2, which then tells the body to breathe slower (at a time when blood-oxygen levels can be dangerously low). It’s called “hyperventilation”, and in a high altitude setting that can be deadly.

    For those of us who like to fly in the hypoxia zone, learning to recognize and deal with hypoxia is a potentially life-and-death skill. Even with that skill, I plan to acquire a pulse oximeter, because I plan to keep flying high (no, not in that sense) for a very long time.

  • Carlgh

    Agree. The Pulse Oximeter is a great pilot tool. An O2 cylinder w/ regulator is for me standard pilot equipment (the old geezer set-up works great). The cylinder can be refilled or exchanged with Aviator’s Breathing almost everywhere. After a long day at altitude, above 10,000, your head can be easily fixed with a few minutes on the gas. SOP for me.
    [BTW. The difference between Medical and Aviator O2 is with and without moisture respectively. In today’s aircraft environments, I find the prohibition against moisture in the gas is – well, old fashioned.]

  • Don R. Bush

    Flying should be all about maintaining safety margins. Consider that Part 135 (air taxi) operations are required to have pilots on oxygen at 10,000 ft. Also consider that oxygen demand is heavily influenced by anxiety. If your workload suddenly increases and (heaven forbid) an urgent or emergency situation developes you’ll surely be hypoxic in short order if not on oxygen already. Avgas is expensive, oxygen is cheap. I like to use it even at 8 or 10k during daylight ops to arrive much fresher and alert. Plus, you never know when you might need or be asked for higher.

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