Aeromedix Flight Blog

There have been a couple of recent reports of pilots fainting on board commercial aircraft. When most people faint, it is not usually a problem. When a pilot faints in flight, it could be catastrophic.

Fainting, or syncope in medical lingo, occurs when the brain does not get enough oxygenated blood to support neurological functioning. Basically, when the brain determines it is not getting enough blood, it says to the body “if you do not get me enough blood, I am going to make you get me enough by making you lie down!”

Fainting most commonly is due to blood pooling in the lower extremities and abdomen so the heart does not have enough blood returning to pump out to maintain blood pressure. This can happen when someone is told bad news, has their blood drawn, has severe pain, and many other reasons. This most common cause of fainting is called a vasovagal response. In these situations, the blood vessels in the peripheral vascular system (e.g. arms, legs, and abdomen) dilate due to stimulation from the vagus nerve which controls much of the automatic nervous system (the part of the nervous system we cannot actively control like heartbeat and blood pressure). The vessels dilate, the blood pools, blood pressure drops, and our brain does not like it.

Dehydration is one of the most common causes of syncope. Dehydration can be from just not drinking enough fluid (to avoid having to urinate in the aircraft), viral stomach illnesses which cause vomiting and diarrhea, to taking a diuretic for high blood pressure which increases fluid loss. Also remember that flying at higher altitudes or in pressurized aircraft causes more dehydration due to low humidity of those environments. Almost any medication which has the side effect of sedation may also contribute to fainting.

Pilots in cockpits are also prone to fainting due to the sitting position which presses on the veins in the back of the leg causing further reduction of blood return to the heart. Anemia or low blood cell count will also predispose to fainting as will advanced age.

When a person faints, they may exhibit jerking movements similar to those seen in seizures. Unfortunately, due to these movements, many people who faint are incorrectly labeled as having had a seizure which has serious implications for driving and flying.

There are other reasons beside vasovagal syncope which can cause fainting such as certain irregular rhythms of the heart, low blood sugar, and panic attacks with hyperventilation. Thus, many emergency room visits and even hospitalizations occur to evaluate a fainting event- particularly when it happens the first time- to search for a cause besides vasovagal syncope. Doctors call vasovagal syncope a diagnosis of exclusion because vasovagal is what we call it when we cannot find another reason.

When a person faints, the best thing to do is to lie them down and raise their feet. This promotes blood return to their heart and raises blood pressure to the brain. A cool wet towel to the face helps but slapping them silly like I once saw another physician do is uncalled-for. Save that ridiculous technique for bad movies. If a person does not wake up spontaneously within a minute or so after lying down, immediate medical attention should be sought.

Prevention of fainting is relatively easy: hydration, hydration, and more hydration. Also, eating something salty can help. Without some salt, you will not retain fluid so all hydration will be lost more quickly. If you have high blood pressure, you should not use salt, but if you do not have hypertension, a bag of potato chips can raise blood pressure slightly to help prevent fainting. (We often see patients, who do not have high blood pressure, develop problems from restricting salt too aggressively!)

When a pilot asked himself if he is fit to fly, one of the important things to consider is whether he is hydrated or has other issues that might make him more prone to fainting. In the two pilot cockpit of an airliner, fainting may be a non event. In a single pilot cockpit, it could be disastrous.

I thought getting “through the fence” fixed with FAA opposition took a long time, but Gary Eaton has worked a couple of years to fix a FAA problem that had no opposition — that “oxygen is oxygen!”

We’ve all heard the ancient cry in the many FAA documents that we must fill our aircraft built in systems with Aviator Breathing Oxygen (ABO). This dates back to the 1950s and 1960s when oxygen came from different sources and was prepared differently. For instance, medical oxygen was forbidden by the FAA because at that time, water vapor was mixed into the oxygen tank for patient comfort and this vapor could freeze in an aircraft’s oxygen plumbing in cold weather and/or high altitudes.

This is a reasonable approach, but for the last forty plus years all oxygen has come from the same liquid oxygen sources and water vapor has not been added to medical oxygen for the same period. With this being the case, it might be time to change the verbiage in the FAA recommendations and documents. Thus was the mission of Mr. Eaton. After a barrage of letters to the FAA and his US Senator, the FAA has agreed to “update the publications” effective October 1, 2012, with each revision cycle (cycles for publications are measured in years, not days or months). As Mr. Eaton says “It may be a bit too early to raise our glasses for a toast. The FAA promised a fix back on October 18, 2007 and they did not make the corrections then.”

What is even more interesting, the FAA now states that their regulations “do not specify purity” and the “FAA Advisory Circulars (AC) are not regulatory and provide an acceptable means, but not the only means, of regulatory compliance” (emphasis mine). So for all these years, when our A&P fill our aircraft oxygen systems with ABO, high priced but identical to medical oxygen, all we were paying for was the name and additional testing to prove it did not have any water in it. It was not even regulatory!

Now, in correspondence to Mr. Eaton, the FAA states they will recommend that supplemental oxygen “meet or exceed the Society of Automotive Engineers International (SAE) Aerospace Standard AS8010 (as revised), Aviator’s Breathing Oxygen Purity Standard” but this is only a recommendation. Given past experience, no one will know what this standard is since the SAE website charges to download the
standard. For the most part, it basically says oxygen needs to be 99.5% pure which means that any modern oxygen source is in “compliance.”

Mr. Eaton’s victory means that finally we can go to our local gas supplier, rent some H cylinders of cheap “medical oxygen,” buy or borrow a two or three tank cascade system hookup, and have our A&P use it to fill our aircraft. (There still is that pesky little FAA regulation which states that only A&Ps can fill installed aircraft oxygen systems but who pays attention to that?”) Oxygen is dirt cheap. Most H cylinders cost about $30 for the oxygen plus tank rent (unless you buy it). A two H cylinder cascade system will fill about 60 average size portable systems or about a dollar a fill. The system should fill about 30 average size built in systems or about $2 a pop!

That brings us to the gas suppliers. If you take your portable oxygen system to you local supplier to fill, if you ask for medical oxygen, they may want a prescription. You can always ask for ABO but that will cost you more dollars. Most of the time, the supplier will not accept the “welding gas” request for filling portable systems. They are not quite that dumb.

Here is my solution: Send me an email with your name and address and I will mail you a prescription for medical oxygen – no charge. It is the least I can do to honor Mr. Eaton’s hard work!

This article was reprinted from the October 2012 edition of Aircraft Owner magazine.

The Federal Aviation Administration’s Civil Aerospace Medical Institute in Oklahoma City offers a dynamic course to help pilots understand physiological and psychological stresses of flight. The one day course is a must for anyone who flies higher than 10,000 feet but is valuable for all pilots.

The course covers the common physiologic problems of flight as well as some of the uncommon ones like decompression sickness. Probably the most important part of the course is the experience in the altitude (hypobaric) chamber which cannot be easily duplicated in an aircraft.

Pilots understand that training and recurrent training is important. Understanding physiologic issues is difficult without experiencing them and then periodically, revisiting the subject for new developments and reminders about how serious these problems may be.

Spatial disorientation is one area that many pilots last felt on a spinning ride at a playground many years in the past. Adults tend to think that it takes that kind of force and velocity to create spatial disorientation because they have not felt the sensation in an aircraft.

The FAA demonstrates that the initiators of do not require major forces using equipment like a Barany chair, a Vertigon, a GYRO, or a Virtual Reality Spatial Disorientation Demonstrator. This is the type of training that might have saved the life of John Kennedy Jr. and many other pilots—both high and low time.

The use and abuse of oxygen and oxygen equipment is covered in the course as well as how to use a pulse oximeter. Understanding why the FAA recommends oxygen as low as 5,000 feet at night is covered as well as high altitude hypoxia in the chamber.

The chamber experience is certainly dramatic. Pilots are taken to as high as 25,000 feet in the chamber and asked to remove their oxygen. They are then asked to do some simple math problems or other simple tasks. Pilots get to watch a video of themselves getting really stupid which is entertaining but incredible educational since the hypoxic victim does not know at the time no can recall how dumb they became.

Rapid decompression from 18,000 to 8,000 feet is another demonstration that cannot be duplicated in an aircraft. Just knowing what that feels like and knowing what to expect is a real eye opener.

Every pilot should go through a personal physiologic and psychological check list prior to each flight. The FAA uses the acronym “I M S A F E”. The acronym stands for Illness, Medication, Stress, Alcohol, Fatigue, and Emotion. Let’s go through this simple check list.

Illness may seem straight forward but there are many pilots who took off with their stuffy noise from the spring hay fever season who suffered incapacitation pain when they could not clear their ears on decent. The stuffy nose did not appear to be important on the ground but aviation presents many unique factors to illness.

Medications can definitely be a problem. No pilot should fly when starting new medications since every drug can cause side effects regardless of the labeling. Of particular concern are psychoactive medications. A psychoactive medication ranges from psychological drugs like anti anxiety agents to simple antihistamines over the counter. Any drug that can affect the brain, whether it is sedating or alerting, can pose problems in the cockpit. Altitude may also increase side effects of medications.

Stress can have significant impact flight safety. Regional airline pilots has claimed, rightly so, that they jobs are harder than the big iron pilots due to all the takeoffs and landings in a day at uncontrolled airports with marginal weather reporting equipment. This is the kind of stress that leads to mistakes—most not so serious but some are tragically fatal. This same kind of stress can affect general aviation pilots. Getting up early for business trips with returns late on the same day is a classic example of stress for a GA pilot.

Alcohol is generally an obvious problem for piloting an aircraft. What also has to be considered is the effect of residual alcohol from the night before and/or a hangover on pilot performance. Also, a hangover will increase the risk of motion sickness, spatial disorientation, and cognitive mistakes.

Fatigue goes hand in hand with stress. It can be a real problem on long flights as well and cause real impairment as the work load increases.

Emotion is a factor that frequently gets overlooked. Going out and doing touch and goes may not be the best way to shake off the anger generated by your teenage kids. The effect of emotions on the thought process and the ability to perform complex tasks is significant.

More information on the CAMI course can be found using this link.

Safe Flying!

Survival at 25,000 feet

I have a friend who was flying at FL210 and rolled the empty copilot seat back which crimped the oxygen tubing to his mask. The ATC tapes of his subsequent radio transmission were beyond ugly. Fortunately, he got this oxygen supply straightened out before a disaster occurred. He was a lucky one.

No one would deny that the top of Mount Everest is a hostile environment for humans. There is no
difference in an aircraft cabin when we fly over the top of the mountains and even higher. By getting
their faster and with an engine or two, our bodies may not be ready without preparation, support, and a
dose of caution.

The most significant issue at the flight levels in an unpressurized aircraft is oxygen. The most significant issue in pressurized aircraft is oxygen as well! Since we now have many production turbocharged aircraft capable and perform better at the flight levels, more and more pilots are setting their altimeter to 29.92. A thorough understanding of the physiology of this harsh environment at these flight levels is important for pilots to understand.

First, let us go over a little bit of physics. At sea level, one quart of air has a specific number of oxygen molecules. Think of a bag of potato chips in your aircraft. If you take a bag up in an aircraft, the amount of atmospheric pressure on the air inside the bag decreases, the space between the air molecules increases, and the bag expands. The expanding pressure may actually burst the bag. Thus, a quart container of air holds fewer air molecules per volume because the air molecules are spilling out of the container.

This means that when we breathe at higher altitudes, each quart of air we take in has fewer molecules
of air which contains about 19% oxygen molecules and 80% nitrogen molecules (the other 1% is minor
stuff). The percentages of each type of gas stay basically the same at all altitudes but each breath (a
fairly constant volume) contains less oxygen molecules and thus, there is less oxygen to be absorbed
into our blood stream.

Normal human oxygen saturation of the blood at sea level is between 95-99%. As we go up, this
saturation drops. It generally becomes problematic about five percentage points below our home
altitude saturation and more significant ten percentage points below the baseline. Where we live
makes a difference because people who live at higher altitudes have more red blood cells per unit
volume to compensate for lower saturations and will be acclimatized and tolerate higher altitudes over
sea level inhabitants.

For healthy people, the altitude where the ten percentage point drop in saturation is reached is in the
eight to ten thousand foot range. If there is underlying lung, heart, or circulatory problems, the blood
oxygen saturation may be much more critical at lower altitudes. Even without medical issues, higher
age causes less resilience to increasing altitude as well. An example might be the person who has
unknown partial coronary artery blockage who has increased heart oxygenation compromise as they increase their altitude with the corresponding decrease in oxygen saturation.

Oxygen supplementation with a mask or cannula increases the number of molecules per inhaled breath
which increases saturation. When we wear a nasal cannula, as we inhale through our nose or mouth
(mouth breathing causes a Venturi effect which still sucks oxygen in through the nose), we may raise
the oxygen percentage in each breath up to 24 or 26%. With a well fitting non rebreather oxygen
mask (the kind with a reservoir bag to collect oxygen from the source between breaths), the oxygen
content in the breath may reach 40%. This is important to understand since it is the basis for the FAA’s
limitation on nasal cannula for use to FL180 or below and the requirement for a mask for altitudes
above FL180. 24 to 26% with a cannula is just not a high enough percentage to keep adequate
saturation above FL180. For higher oxygen percentages needed above FL300 in un-pressurized aircraft,
pressure oxygen systems like those used in the military are necessary.

Here is a real world example of how one could get into a problem: We are flying our Cirrus at FL250
enjoying a 100 knot tailwind cruising from Santa Monica to Houston. We are on a mask with an oxygen
flow rate of 2.5 liters per minute (the FAA recommended flow rate is 1 LPM/10,000 feet) and our
saturation is 92%. Not bad for a flatlander. Our dog decided to change their napping position and
unbeknownst to us, his paw pulls the tubing out from oxygen tank regulator.

How long before we notice something is wrong? Wrong question Bucko! How long do we remain able
to perform flight duties is the correct question and is called “Time of Useful Consciousness.” (See Chart
1 below). You will not be dead in seconds but you will not respond to those F-16s buzzing your windscreen. If you are lucky and do not progress to death, you may wake up when the plane runs out of gas and descends to “thicker” air. You might even get it together enough to pull that Cirrus’ parachute. Another concern with oxygen masks is removing them to drink or eat at altitude. It does not take long with the oxygen mask off to become just distracted enough wiping that mayonnaise off your cheek to forget to put the oxygen mask back on before “goofiness” sets in!

Chart 1

Time of useful consciousness (TUC) is defined as the amount of time an individual is able to perform flying duties efficiently in an environment of inadequate oxygen supply. It is the period of time from the interruption of the oxygen supply or exposure to an oxygen-poor environment to the time when useful function is lost, and the individual is no longer capable of taking proper corrective and protective action. It is not the time to total unconsciousness. Smoking drastically reduces oxygen intake efficiency, and can have the effect of reducing tolerance by 3,000-6,000 feet. In addition, the TUC can be reduced by 30 to 50 percent when the decompression is rapid because of the sudden outward flow of oxygen from the body’s cellular tissue.

The proper oxygen system and flow rates are critical at the flight levels. This is not just “I’m getting a headache territory but cemetery property. The only way to truly know if you are getting enough oxygen is to use a pulse oximeter. Since there are excellent American made ones which have come down in price to as little as $100, there is no excuse not to have a pulse oximeter on board. If you really want safety, buy a pulse oximeter with saturation alarms however, these will run you about $600 or more depending on features.Remember even in pressurized aircraft flying high, the cabin differential might still put the cabin at, say, 9,000 feet which means an older pilot, a smoker, or a passenger with lung disease might need additional oxygen supplementation.

Since everyone is different, the oxygen requirements and flow rates the FAA mandates may or may
not be enough. The regulations basically state you must use oxygen if over 12,500 feet if you are there
for more than 30 minutes or anytime over 14,000 feet. These rules stem from the 1950s before pulse
oximetry was available and were based on some postulated physiology but mainly geopolitical
reasons. Oxygen systems were heavy and expensive in the 1950’s and the FAA apparently did not want to force general aviation aircraft in US to be required to use oxygen. Thus, the 12,500/14,000 rule will
allow the crossing of all the mountain ranges in the lower 48 and GA equipment may proceed on their
merry way. However, many people really should use oxygen at lower altitudes. Even going on oxygen
for 30 minutes prior to landing will help clear the senses and help make sure you aren’t on final to that cow pasture next to the airport.

In-Flight Oxygen Emergencies

A plan for emergency descent is a critical requirement for high level flight. In an unpressurized aircraft, emergency descents are not frequently taught despite this training being commonplace for pressurized aircraft. Each aircraft is different and the Pilot Operating Handbook should be consulted. I recommend that although the descent steps should be memorized, a small 3” x 5” card should be clipped to the yoke during all flight above 18K. This way, if you are suffering from hypoxia and/or disoriented from the noise and accompanying dust after an explosive decompression, you can see what you are supposed to do without fumbling for the checklists.

In an unpressurized aircraft, descend first and then check the oxygen supply. You may not have time to
trouble shoot the oxygen system while maintaining altitude so make the descent first. Notify ATC when you can but they become last priority in an oxygen emergency.

For pressurized aircraft, lack of pressurization on ascent (a la Paine Stewart’s tragedy) or a faulty oxygen system may go unnoticed unless you are paying attention to the cabin altimeter, visual flow indicator, and a pulse oximeter. Make at least one of these instruments part of your scan.

There are other important aspects of high altitude flight. Hydration is an important factor. As we
go high, pressurized or not, the amount of vapor in the air decreases dramatically—basically to zero
percent humidity. Since with every breath we take, our lungs humidify the air to almost 100%, at
altitude or in a pressurized cabin, we lose that fluid with every breath. Add to that the fact that the dry ambient air leaches fluid from our skin and dehydration becomes a major factor.

Some might say that dry skin and a mild headache due to dehydration might not be a big problem.
The issue here is not necessarily a simple headache, it is the increased risk of deep vein thrombosis (DVT or blood clots in the major veins) which may result in a pulmonary embolus (PE). A PE is when the clot breaks loose and clogs up your pulmonary arteries. This clog from a PE can be a minor event or precipitate an instantly deadly cardiac arrhythmia.

My rule is that if you do not have to urinate every three hours at altitude, your tank is not full. Your kidneys are a better physiologic monitor of your hydration status than generic suggestions on the number of glasses of water to drink per day so monitor your urinary output. You can always carry portable urinals with you in your aircraft for those times “you just got to go”

Another important factor in aircraft with those big canopies is sun exposure. Sun block is a requirement for high altitude flight in aircraft with minimal shade. Sun causes three types of skin cancer and will prematurely age those pretty pilot faces out there.

Although I should not have to say it, quality sunglasses are also a must. Yes, you might be able to see
fine without them, but in addition to the increased eye fatigue factor, bright sunlight contributes to the
formation of cataracts.

Yet another issue in non-pressurized aircraft is corneal hypoxia. There have been a few studies which
show decreased visual acuity in low oxygen environments—especially in people who have had LASIK type surgery. This is due to the reduced oxygen contact with the cornea. There is not much you can do about this factor but some ophthalmologists recommend daily intake of flax seed oil which may increase tear duct production and reduce the hypoxia effect.

Dog and cats will definitely suffer hypoxia with altitudes over 10-12,000 feet msl. Most pilots just let their pets sleep but this may not be the best approach for your pet’s health. There are a few pet-specific solutions that will provide your dog/cat with adequate oxygen when flying at high altitudes. I personally recommend the products from 4Paws Aviation. Although this equipment can run $100 or more, these oxygen hoods are the best way to administer oxygen to pets in aircraft.

Finally, there is still another issue for unpressurized aircraft occupants regarding middle ear pressure equalization. At high altitude, a significant amount of air escapes from the middle ear chamber through the Eustachian tube. On descent, air needs to return to the chamber or the classic ear “squeeze” will occur. This is due to the Eustachian tube being a relative one way valve in some people. This is also complicated by dehydration at altitude which thickens mucous secretions that also block the tube. Gentle Valsalva maneuvers on descent will help alleviate the pressure but must be done at the first sign of pressure and repeated frequently. If the sufferer waits till the pressure is really bad, it is much harder to clear the vacuum due to the increased pressures. High pressure equates to significant pain and possible damage. If simple Valsalva maneuvers do not work, trying the maneuver while simultaneously swallowing may help but this requires some coordination to get right.

High altitude flight is not dangerous but, like many things in piloting aircraft, it must be addressed with respect and preparation. It is not a simple walk in the woods.

Post Script: Viagra and AMS

When Viagra is mentioned anywhere, it creates a lot of interest—especially in the male dominated
aviation community. Viagra has been mentioned as a preventative for acute mountain sickness (AMS) for people who develop AMS at altitude. AMS has been shown to occur in pilots and passengers who fly above 6,000 feet both in absolute and cabin pressure. How often and how significant AMS occurs is up for debate.

AMS is a collection of non specific symptoms which are caused by low barometric pressures and hypoxia. It was thought to be exacerbated by a type of breathing pattern (i.e. long pauses) which was originally described during sleep in mountain climbers. I documented this same breathing in pilots during the wakeful state when we introduced pulse oximetry to general aviation and were testing various types of oximeters.

The symptoms of AMS include nausea, vomiting, anorexia, insomnia, dizziness, fatigue, and/or lassitude.
There are more serious types of AMS called high altitude pulmonary edema (HAPE) and an off-shoot called high altitude cerebral edema (HACE). Since most altitude sickness occurs with overnight exposure
or at least prolonged exposure (defined in a recent study as three to nine hours), this would tend to
eliminate most GA flights from being at risk for AMS. Interestingly, this may indicate that jet lag associated with long airline flights may not be time zone related but to AMS.

So how did Viagra get into the mix of this discussion? Since blood pressures in the pulmonary vessels appears to be increased related to altitude and this is thought to be one of the factors in HAPE, Viagra, with its vasodilatation effect could have a beneficial effect—at least theoretically. Since Viagra (and Cialis and Levitra) all affect color vision, their use is not permitted by the FAA. Thus, help with the mile high club cannot be augmented by the use of Viagra for AMS by required crew members.