Fly Well

Diving to great heights

March 1, 2010

“Sometimes, all I need is the air that I breathe and to love you,” sang The Hollies in 1972. Nice sentiments, but wrong. You need air—not sometimes, all of the time. Many pilots scuba dive, always descending with a carefully checked tank, but many ascend without oxygen. Federal Aviation Regulation 91.211 states that a pilot of an unpressurized aircraft shall not operate from 12,500 to 14,000 feet for longer than 30 minutes without supplemental oxygen. Above 14,000 feet, oxygen has to be used by the crew, and above 15,000 feet it must be provided for everyone aboard.

There are two key gases in the air we breathe: oxygen (roughly 20 percent) and nitrogen (78 percent). At sea level, atmospheric density ensures that our blood is approximately 100 percent oxygen saturated unless one has a lung, heart, or blood disease. With increasing altitude, the atmosphere thins, so each breath contains less oxygen—at 18,000 feet, density is half that at sea level. Insufficient blood oxygen saturation is called hypoxia. Additionally, diminishing pressure allows internal gases to expand in the sinuses, dental fillings, or colon, causing embarrassing “gas leaks.”

With explosive decompression, time of useful consciousness may be three minutes at 25,000 feet—or mere seconds at 40,000 feet—for a well-oxygenated, healthy pilot. Practicing donning a mask quickly and with your eyes closed is critical because decompression causes cabin fogging in addition to the intellectual fog and pain from rapidly expanding internal gases. But decompression is rare today and irrelevant to those who fly unpressurized aircraft. Hypoxia training commonly mimics decompression but does not broach slow-onset hypoxia or failure of an aircraft to pressurize.

I visited Dr. Paul Buza in Melbourne, Florida—his hypobaric chamber incorporates flight and air traffic control simulation and each exercise is videotaped. His protocol mimics various situations and he has trained many pilots and controllers. “As a diver I became interested in hypobaric medicine. Pilots have similar issues, so I developed this center.”

Everyone gets hypoxic differently. Buza screened a video of four pilots “flying” his chamber—one became euphoric, one slept, one acted incoherently, and one was fixated and unresponsive to ATC commands. Therefore, each pilot should learn and note his or her symptoms at the onset of hypoxia—the hypoxic brain may quite blissfully ignore the strident call of a hypoxia alarm. So the secret is simple: prevention.

Hypoxia, like fatigue, may play a role in aviation accidents from induced errors or by precipitating fatal events such as heart attacks or abnormal cardiac rhythms in pilots with preexisting heart disease. But what are the long-term consequences for pilot and passenger health? Chronic hypoxia may cause cell damage that declares itself at a later date. We simply do not have the data to know this for sure, but why take the chance of slowly killing heart, brain, kidney, or other cells when simply breathing oxygen could prevent this?

Carrying oxygen, either fitted into the aircraft or taken aboard as a compressed gas bottle, is a shrewd move. One also needs either nasal cannulae (which the FAA limits to 18,000 feet) or masks. On-demand regulators allow oxygen to flow upon breathing deeply and preserve the supply. In the event of carbon monoxide contamination, having oxygen on board can save your life. Beware of fire hazards from petroleum-based products such as Vaseline when using oxygen.

A pulse oximeter is another sensible purchase; this device clips over a finger and senses oxygenation and pulse rate (do not wear nail polish). View the readings regularly—I have an entry on my checklist—and if you see low saturation, breathe deeply and descend, being wary of hyperventilation. Change its batteries frequently and keep a spare aboard. Contrary to popular belief, you do not need a doctor’s prescription for these devices. A preflight checklist for the oxygen system is a good idea and the PRICE acronym works well: pressure, regulator, indicator, connections, emergencies.

Nitrogen can also make mischief at altitude. Just as divers can suffer from decompression illness (“the bends” or “Caisson disease”), so can pilots. At sustained lower atmospheric pressures, nitrogen dissolved in the blood and tissues can bubble out of solution and block blood vessels everywhere. This can manifest as confusion, headache, fatigue, partial visual loss or floaters, joint and muscle pain, a mottled or marbled skin rash, a tingling sensation known as formication (like ants crawling on your skin), sudden incontinence (that got your attention!), or dry cough (“the chokes”). Prebreathing oxygen and continuing this throughout the flight limits the risk. Rapid rates of climb, time at altitude, poor oxygenation, age, obesity, and dehydration all raise the risk. If one suspects this problem, breathe pure oxygen and descend rapidly. On landing, obtain immediate medical attention for all on board and do not ascend again until cleared by a physician. Monitor the oxygen supply being refilled, just as you would check that the correct fuel has been pumped. The cost of all I have suggested is small—and the savings from bent airplanes or lives lost is large. We all need someone to love, and we all need the air that we breathe—all of the time.

Dr. Jonathan Sackier is a surgeon and instrument-rated pilot who lives in Charlottesville, Virginia. E-mail the author at jonathan.sackier@aopa.org.