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A couple of years back I purchased a pulse oximeter to monitor for hypoxia. Principally due to an experience with carbon monoxide and a broken exhaust manifold. Never thought to monitor at typical cruise altitudes... until yesterday.

Quick two hour flight up to Lake Erie islands for lunch taking advantage of nice weather. Cruising at 11,000 ft. settled in for an hour or so of cruise so I pulled out the flashlights, CO monitor, back up VHF radio and pulse oximeter and checked the batteries.

All was well until I tried the pulse oximeter. It read 74 (my typical on the ground here locally is 95). Right seat pilot had a reading slightly lower. Had to be wrong, right?

Take a look at this chart:


approach-to-hypoxemia-3-638.jpg [ 66.53 KiB | Viewed 17963 times ]


And we've all read about the recommendation to use oxygen at night above 5,000 ft.:


Hypoxia-chart-750x330.jpg [ 51.19 KiB | Viewed 17963 times ]


I routinely fly (without oxygen) in cruise between 9,000 - 11,000 ft. Less turbulence, traffic, higher TAS and better fuel economy. I'm rethinking that approach.

Really good feedback and comments received offline on the post but one in particular hit home that I wanted to share.

A Chapter 21 member recounted an AME's suggestion from an Oshkosh aero-medical seminar on the use of oxygen and hypoxia. Yup - Find Your Number.

We're all different - age, body type, health status (both acute and chronic medical conditions), etc. So, the regulations regarding oxygen use may fit a healthy 22 year old but not everyone.

To find your number you'll need to go flying.

Take (or borrow) a pulse oximeter and climb to a cabin altitude where your oxygen saturation falls to and settles at 90%. That's your number. It may be 8,000 or 10,000 but for the majority of us it is not 12,500 ft. and above. Below 90% you are "on the bottle".

Of course, the use of oxygen at night at cabin altitudes of 5,000 and above still holds true. And the number is not static. Recovering from a respiratory illness, a general change in your health status, certain medications, smoking, seasonal allergies, etc. may require a change in your number.

So the take away message here is you may be experiencing mild hypoxia well below the altitudes in the regs. So, go find your number and remember to check it often.