Oxygen For The Pilot


    Sport Aviation - October 1999

    Most homebuilders never think about using oxygen but with the newer, high performance aircraft like the Glasair and the Lancair, flying high without oxygen can be dangerous or even deadly. Many of us who have to fly production aircraft also take a lax approach to oxygen supplementation. Almost everyone has some degree of visual impairment due to decreased oxygen levels in our blood even at this relatively low altitude. The impairment actually worsens as we get farther and farther past our 40th birthday. 

    Try this little experiment. Pick a CAVU night, borrow a portable oxygen system and fly about 8,000 feet MSL. Fly for 15 minutes and then put on the oxygen. Watch . . . all of a sudden you will probably notice it looks like someone turned up the dimmer switch and colors also become more intense. Oxygen levels go hand in hand with pressure altitude. When we take a breath at sea level, we inhale air which is approximately 20% oxygen. At ten thousand feet, we inhale the same 20% but the number of oxygen as well as other gas molecules is fewer per breath because the atmospheric pressure is not pushing them together (e.g. less densely packed). Thus, for each individual breath, we absorb less oxygen. Some of this can be compensated for by hyperventilating but cannot be done continuously as hyperventilation has its own adverse effects.

    The FARs state that if we fly over 12,500 feet for more than 30 minutes, we need to use supplemental oxygen. If we fly over 14,000 feet, we need oxygen immediately and continuously. The FAA oxygen regulations are antiquated and not based on the cognitive changes that can occur in the pilot. The 12.5/14 rule is based on geography, the high cost of oxygen systems and their lack of portability in the era in which the regulations were written. 

    At 12,500 feet, one can fly over mountain passes without requiring oxygen, leaving almost all the continental U.S. airspace open to those who did not have oxygen systems. The rules had little to do with the possible impairment of the pilot who flies at altitude. 

    With recent advancements in medical technology, oxygen saturation which reflects the amount of oxygen in the blood stream, can be determined in the cockpit for all pilots. Using pulse oximetry, pilots can objectively demonstrate the need for oxygen based on their personal physiology instead of guessing. 

    Pulse oximetry in the cockpit has become as important for those who fly at higher altitudes (which I define for this purpose as 8,000 or above) as altitude chamber training. Itzhak Jacoby, Professor of Preventative and Aerospace Medicine at the Uniform Services University of Health Sciences in Bethesda, has shown significant impairment in pilots at only 10,000 feet by testing them with a computer program used in the space shuttle. The program, called SCAT, tests memory, accuracy and response time — all of which were adversely affected at this relatively low altitude. He also has documented dramatic and speedy improvement with the administration of oxygen. Portable oxygen systems are cheap and plentiful. Refills have become much easier and can even be done with a set of larger cylinders by the pilot himself. Other than the cost and time of refilling the bottles, there is no down side to using oxygen. It cannot be used too low nor will it cause negative side effects. The use of oxygen not only improves thinking but will reduce fatigue and improve the energy levels of the pilot. 

    One recurring myth must be dispelled — there is no difference between aviation, medical, welding and other oxygen types and has not been for many years. All oxygen is now derived from liquid oxygen and the concern over water content is nonexistent. Even officials of the FAA agreed with this interpretation at AirVenture ’99 this past summer stating the regulations need revising. I personally just tell my tank refiller that I am using it for medical purposes so the gas house does not flip out about filling aviation tanks. I recommend oxygen conserving nasal cannulas to 18,000 feet and the FAA requires masks over flight level 180. Flow rates are set by pressure altitude but are best set by using a pulse oximeter to follow oxygen saturation levels. 

    To determine the oxygen flow rates to use and maintain, the pilot should determine his home base saturation first. When flying, he should start using oxygen when the saturation drops five percentage points and must use oxygen when the saturation drops ten points. The saturation level should then be titrated with the oxygen flow rate back up to the home airport level. With inexpensive, small and portable oxygen systems, there is no longer an excuse for pilots to become impaired at any altitude due to lack of oxygen. 

    (Dr. Blue is a member of the EAA’s Aeromedical Council. He is Board Certified in both Family Practice and Emergency Medicine and an ATP rated pilot. He flies a Cessna 340, the Flaglor HighTow biplane and is starting to build a Super Rebel. He can be reached at brentblue@dial-a-doc.com.)

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