Hypoxia paper

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BY: DR. PAUL W BUZA, D.O., F.A.C.N. 1ST EDITION 2016

The Pilot’s Practical Guide to Altitude

Physiology

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Dr. Paul W. Buza, Medical Director of SAMI

Preface

Pilot’s Practical Guide

to Altitude Physiology

This book is designed to be practical for the busy pilot who can quickly learn and review the essential fundamentals of altitude physiology. The book can be read in less than 1 hour refreshing the pilot’s memory as to the essential fundamentals of hypoxia and other related inflight issues. After reading the book the pilot should be aware of the dangers of cabin depressurization as well as the need for oxygen supplementation in

unpressurized aircraft. A significant portion of the information contained within this book is original arising from the research performed at the Southern AeroMedical Institute (SAMI) and should be interesting for pilots who have been through prior hypoxia chamber programs. Of particular emphasis, is the extensive research and experience in slow onset hypoxia which differs significantly when compared to explosive or rapid models.

Most of the new and original information that is found within the book originated from the high altitude chamber at SAMI. The successful integration of flight simulators further integrated with ATC communications while flying true depressurization scenarios has revealed further insight into the human experience of hypoxia. To date, more than 3000 pilots have now flown the slow onset hypoxia profile since 2006. Much of what was learned from that experience is now available for your review and it is my hope that you can learn more about your physiology in flight to keep you and your passengers safe.

Good Luck and Enjoy!

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Table of Contents

Introduction…………………………………………….……...4

Trapped Gasses……………………………………….……...5

Hypoxia Into Thin Air……………………………..….….…9

Hypoxia Sensations……………………………..…………10

Hypoxia Signs…………………………………………..…….18

Hypoxia Fingerprint……………………………….……….23

Spectrum of Hypoxia………………………………..…….24

Crew Resource Management……………………..…..38

Summary…………………………………………………….....44

Appendix……………………………………………………..…45

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Introduction

We spend almost all of our time focused on our aircraft and the potential weather. How much time do you focus on yourself and crewmembers? Not much. We tend to be macho and minimize our own physical limitations to focus primarily on the needs of aerodynamic flight. As noble as this may be, what we may not appreciate is that the physical rigors of flight can impact and diminish our performance. Being unaware of this impact is a form of “loss of situational awareness “that can increase our level of fixation.

An example is in the initial phase of descent you notice mild pressure in the right ear. There is a significant crosswind that you are focused

on and as you approach the runway you now notice that the pressure in the ear is building up and now there is mild pain. Since you are in the final approach you do not consider the pain to be significant until suddenly the pain is excruciating and very distracting as the wheels are almost ready to touch down in the strong cross wind.

As we will soon learn, the highest probability for a debilitating “ear squeeze” is in the final phase of descent. This book focuses on the most likely scenarios that pilot’s may encounter as it relates to altitude physiology.

Let’s begin with trapped gases.

Not a good time to rupture your ear drum because you forgot to equalize your ear during descent.

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Trapped Gases

As we ascend the volume of a gas enlarges due to decreased pressure. Conversely, when we descend from altitude, the volume of a gas decreases. We have regions of air spaces within our bodies. For our purposes we will focus on the ears, sinuses, gastro-intestinal tract and dental air spaces from underlying bacterial infection. If the air spaces can communicate freely with the surrounding environment there usually is no difficulty with gas expansion or contraction experienced by the pilot.

However, if the air space cannot communicate freely the air space becomes “trapped”. The greatest net change in pressure is that which is closest to sea level. As a rule, it is worth remembering that 18,000 feet represents one half the atmospheric pressure where the volume of a gas will double in size. Knowing this allows us now to look at specific scenarios where pilots may experience severe pain or discomfort due to “trapped gases”.

Key Point: Trapped gases can become problematic in all phases of flight especially in the final phase of descent.

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Trapped Gases

Ear Squeeze Middle Ear Equalization

The ear drum is very thin and fragile! It simply cannot withstand significant pressure of any type. As you descend the pressure increases, thereby pushing the ear drum inward. Your job is to equalize the eardrum by exerting pressure thru the long and narrow Eustachian tube that opens up in the back of your throat. It is crucial that you equalize as soon as you feel any type of pressure in the ears. Ear pain is not to be tolerated- but mitigated! Unresolved ear pain on descent can lead to rupture of the ear drum.

Take the time to learn what technique works for you. Equalizing the ears can sometimes be easily accomplished with swallow. Sipping a drink or chewing gum can be helpful. If not, the Valsalva technique applies mild pressure to the Eustachian tube to assist opening the canal. This is accomplished by pinching the nose closed, closing our mouths and then forcing pressure by gently blowing air upward to open the tube. Use only enough force to gently open the tubes. Too often, we notice pilots blowing so hard as if they were Dizzy Gillespie on trumpet.

By this time, it’s too late - your ear is trapped! Blowing harder will not open the tube. The ear is what we call “locked” and will not equalize unless you hold your descent and if necessary ascend to decrease the pressure on the tube at which point the Valsalva technique is likely to be more effective. This is one of the primary reasons why we don’t fly with a head cold because the Eustachian tube is obstructed with mucous and congestion.

Key Point: Always equalize early when you feel pressure in the ear. Never ignore the pressure or the pain.

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Key Point: Time to go see the dentist!

Trapped Gases

Sinus Squeeze A sinus squeeze can occur in any phase of flight. Expansion of air volume on ascent or contraction of air volume on descent can irritate the sinus wall. The pain can come on gradually or be sudden in nature not to mention very intense! The pain is located most often around the

eyes and can be very sharp in nature causing the eye to tear. There is no technique available for you except to “look past the pain “and stay focused on your flight! Depending on the intensity of the pain you will need to make a decision to abort your flight. The Valsalva technique is ineffective and may worsen the pain. Like the ear it is unwise to fly with a head cold due to congestion within your sinuses. You can try blowing your nose although this may only worsen the pain in

the short term. Smokers and pilots with allergies are more prone to sinus squeezes.

Tooth Squeeze You may be unaware that you have a cavity where bacteria have formed gas inside your tooth. As you ascend the volume of that gas expands pushing directly on the nerve. Ouch! The pain comes on suddenly and can be very intense! Imagine being at the dentist without anesthesia. Double Ouch! These pains can be mild or excruciating resulting in significant distraction or even incapacitation. This is most likely to occur on ascent and or soon after leveling off at cruise altitude. The immediate solution is to descend the aircraft or increase your cabin pressure which reduces the size of the trapped bubble taking pressure off the nerve.

Congestion in the sinus cavity may cause pain upon ascent or descent.

Key Point: A sinus squeeze can be very painful and debilitating in flight. This is a great reason not to fly with a head cold.

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Trapped Gases

Abdominal Bloating Fly Lean, Mean, and Clean

At any given time, our gastrointestinal system is composed of approximately 50% of air. Every time we swallow we are essentially swallowing air. Hence, this air can expand on ascent. If not properly mitigated this can lead to distraction on the flight deck due to: bloating, abdominal pain, sweating and nausea. In severe cases it can result in a slowing of your heart rate leading to loss of consciousness. This phenomenon is particularly noticeable between 15,000-25,000 feet of cabin altitude.

Mitigation strategies include:

Avoid gas forming foods prior to flight! Each person is different but most would agree that refried beans, cabbage and salads can result in bloating. Be aware of the particular foods that you are sensitive too and avoid them several hours prior to flight. Also avoid heavy “fatty” meals as the fat load can sit quite heavy on your stomach. “Fly Lean and Mean”. The definitive

resolution is the Free Air Release Technique. Don’t be bashful! “You’ve got to do what you’ve got to do”.

Key Point: Avoid gas forming foods before flight.

Avoid foods that cause gas and bloating before flight.

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Hypoxia Into The Thin Air

As soon as the “wheels are off the ground” the available oxygen for us to breathe begins to reduce. As we increase in altitude there is a corresponding decrease in atmospheric pressure. The percentage of gas that you breathe remains the same while the pressure continues to decrease. You can’t notice this lower pressure and continue breathing normally as if everything is OK. However, with each seemingly normal breath you take the amount of oxygen is decreasing till such a point it begins to take an effect.

Let’s memorize that at 18,000 feet the ambient pressure is ½ that of sea level. If sea level pressure is 760mmHg then at 18K it is now 380mmHg. Oxygen represents 21% of that pressure so the oxygen is reduced from

160mmHg to now only 80mmHg. This is not sustainable for us and after 30 minutes we will be incapacitated. Later we will learn the “Time of Useful Consciousness” (TUC) tables.

This further emphasizes the importance of cabin pressurization systems and or the oxygen support systems in high altitude unpressurized aircraft.

Feet Oxygen Effective

Performance Time

40,00 29 mmHg 10-15 seconds

30,000 47 mmHg 1-2 minutes

25,000 60 mmHg 3-5 minutes

18,000 80 mmHg 20-30 minutes

15,000 90 mmHg 30-40 minutes

8,000 115 mmHg Normal

Sea Level 159 mmHg Normal

Key Point: As we ascend in altitude the percentage of oxygen remains the same while the pressure of oxygen is reduced.

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Hypoxia

Hypoxia Signs and Sensations Sensations (symptoms) are that what you feel and cannot be seen by your crew members. Examples include dizziness, numbness, tingling sensations and tunnel vision. If not communicated your crew members cannot know what you are feeling or perceiving. I don’t like the term symptoms as it implies that we are sick. I rather prefer the term “sensations” as it relates to how you feel during a physiological change.

Signs are that what we can see in ourselves or our crew members. Examples include tremor, cyanosis (blue lips and fingernails) and slurred speech.

Hypoxia signs and sensations are highly variable amongst pilots. Also variable is the intensity of each sensation as some are quite mild and others are rather intense.

In general, hypoxia is a painless and non-anxiety event which explains the insidious nature and therefore dangerous nature of hypoxia. There is no better example of hypoxia than the Boeing 737 Helios event in 2005 where the crew failed to identify slow onset hypoxia due to failure of pressurization on ascent. The crew was unaware on takeoff that the cabin was not pressurizing. It only took 14 minutes from takeoff for the crew to become incapacitated resulting in the death of all 121 on board.

The key message is that the signs and sensations are not always as obvious as we would like them to be. We must have a higher index of suspicion to detect hypoxia. So let’s now take a closer look at the different sensations and signs associated with failure of cabin pressurization.

Key Point: Sensations and signs of hypoxia are high variable amongst pilots and may not always be so easy to detect.

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Sensations

Dizziness or Lightheadedness “I Feel a Bit Woozy”

Dizziness is one of the most common sensations reported by pilots. It tends to be more noticeable in a rapid decompression and rather mild in the slow onset depressurization. It is non-threatening in nature and not associated with anxiety or vertigo (violent spinning like sensation). If vertigo does occur, it is due to an inner ear disturbance most likely due to barometric changes affecting the inner ear.

Although reported in the literature, nausea is not a common symptom of slow onset hypoxia. If it occurs, it is most likely due to stomach or colon distention from gas expansion.

Nausea however can be seen in general aviation unpressurized aircraft where prolonged flights of several hours or more at altitudes of 8,000-15,000 feet can lead to headache and nausea (the Denver Effect). Typically, we wouldn’t expect to get dizzy while seated on the flight deck in a relaxed environment. So if dizziness occurs in this setting we can consider this to be a possible sensation of hypoxia.

Key Point: Light headedness is one of the most common sensations of hypoxia.

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Sensations

Numbness and Tingling The Autonomic Flush

”My Face Feels Warm”

Numbness and tingling like sensations are one of the most common and reliable sensations of hypoxia. It tends to occur mostly over the hands and feet as they are the farthest parts of the body away from the heart.

However, pilots commonly report other regions of the body as well including the upper arms, thighs, lips, ears and face. Each pilot is different so be aware of the sensations reported by your crew members. They will not all be the same!

One of the most reliable sensations is the “Facial/Chest Flush”. This is

unique and you should be highly suspicious of hypoxia if this occurs. The sensation here is that of warmth over your chest and face. Almost as if like a warm towel your mother may have used to lay over your chest and face to break up congestion when you had a bad cold as a child. Sometimes you may feel your heart pounding as well with the Facial/Chest Flush. In a depressurization the ambient cabin temperature would cool while suddenly you feel warm over the face and chest. This is an excellent clue to hypoxia!

So if you feel a bit dizzy and your hands and feet begin to tingle along with a warm sensation across your chest and face, you are now well on your way to hypoxia.

Key Point: Numbness and tingling along with a warm facial flush are common sensations of hypoxia.

Figure 1: Experiencing numbness and tingling in the extremities is an excellent sensation to recognize hypoxia.

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Sensations

Vision Impairment “My Vision is Different/My Scanning is Slow”

The most common visual impairments reported by pilots:

1. Tunnel vision

2. Loss of color vision

3. Harder to focus or concentrate on the instruments

Visual changes are noted more easily during night flights or rapid/explosive decompressions.

Unfortunately, they are difficult to notice during slow onset hypoxia until you don your mask which of course defeats the purpose. This is due primarily to the fact that you are fixating and very focused on your instruments. You may not notice that color is beginning to fade or that you are experiencing loss of peripheral vision- Tunnel Vision. Once you don your mask, suddenly the vision seems to improve dramatically even though you denied vision loss while becoming hypoxic.

Figure 2: Normal vision

Figure 3: Tunnel Vision/Fixation

Figure 4: Loss of Color

Key Point: Even though vision is most sensitive to hypoxia, it is often missed by pilots as they fixate on their instruments.

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Sensations

Changes in Our Breathing The Pilot’s Deep Sigh

When our oxygen availability decreases during depressurization we would assume that we would feel a strong sensation of “shortness of breath”. During slow onset hypoxia this simply does not happen and is probably the single most important reason to the dangers of hypoxia. If we did feel such a strong sensation of not being able to breathe our situational awareness would be immediately established and we would instinctively go for our masks.

When slow onset hypoxia occurs some pilots will notice a mild sense of air hunger but it does not result in anxiety or panic. Some will notice that they “have to take deeper breaths and often this results in the classic “deep sigh”. This occurs more frequently when the pilot is actively engaged in talking such as with ATC as an example.

So the sense of change in our breathing is noted to be subtle and the sense of air starvation is often mild and non-threatening in nature.

Key Point: Hypoxia related shortness of breath is not associated with intense anxiety and may be hard to detect.

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Sensations

Weakness My Arms Feel Like Lead Bricks

A common sensation that isn’t often reported is the sense of your arms feel very “heavy”. This also includes the sensation that suddenly your head feels heavy and you feel weak.

This is noted primarily while using your hands to manipulate instrumentation, especially when outstretched forward to change radio frequencies or direction. It is more difficult to notice your arms while resting at your sides or in your lap. Since we are seated almost all the time in flight you won’t notice

your legs being heavy. But as soon as you stand up it is readily noticeable and you will have an intense desire to sit right back down.

It may not seem that holding your arm out horizontal against gravity requires significant oxygen but in fact it does. Try it at sea level where you hold both arms straight out in front of you. See how long you can hold that position before you start to feel very heavy. I think you’ll be quite surprised.

So add this sensation to the list of clues for hypoxia.

Key Point: Muscles will weaken quickly during hypoxia.

Figure 5: Reaching for instruments may be difficult during hypoxia.

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Sensations

Headache? Headache is reported in the literature to be a symptom of hypoxia. This has not been my experience in flying over 3000 pilots for hypoxia training. When it is reported it is almost always associated with a sinus squeeze that we have already discussed. Here we need to divide this phenomenon in 2 different categories: acute hypoxia (which occurs over several minutes) and chronic hypoxia (which occurs over hours).

The headache associated with acute hypoxia (less than 15 minutes) is almost always associated with a sinus squeeze which is related to a trapped gas phenomenon that we have already discussed. In the slow onset hypoxia of 10-15 minute duration, headache is almost always related to a sinus squeeze as well.

However, long term exposure of 8-15K feet for several hours can lead to a significant headache not related to trapped gases. This is more related to long term exposure at the lower altitudes- “The Denver Effect”. This in combination with dehydration can result in a significant and debilitating headache. Oxygen supplementation and fluid hydration should be helpful here to resolve the headache.

Consider oxygen supplementation if you begin to experience a headache if not related to a sinus squeeze.

Key Point: Headache is not a common sensation of short term hypoxia exposure unless related to a sinus squeeze.

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Sensations

Shortness of Breath? If we cannot breathe we immediately panic. We are intensely aware of our situation.

So it is essential we take a moment to further discuss shortness of breath. You know the sensation. Imagine that you are swimming underwater trying to reach the other side of the pool. You begin to sense that you are in need of air but you want to keep going. You know exactly how far you can push it till that last second when you must surface quickly and take that breath. Well that does not happen at altitude! You will not have that benefit knowing exactly how long you can go without donning your mask. Later you will learn that you will fixate on your instruments without that sense of panic until you become incapacitated. What pilots do notice are changes in their breathing such as feeling the need to take deeper breaths? Some will notice a mild sense of shortness of breath without associated anxiety. The key difference is the absence of anxiety that almost always accompanies the sensation of not being able to breathe. If this was in fact the case, we probably would not need the training as it would be a universal sign to reach for your oxygen mask regardless of the ascent profile.

Key Point: Shortness of breath during hypoxia is not associated with anxiety and may be difficult to detect. In my view, this represents the most important vulnerability for the crew during a cabin depressurization.

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Signs of Hypoxia

Signs are what we can see in ourselves or others. Signs are objective while sensations are subjective.

Both are important to recognize and communicate!

During a cabin depressurization there are ample opportunities to see changes that are occurring amongst the crew.

This also includes changes in the crew’s performance (or lack of), speech patterns and mood.

The better we know our crew members, the easier it is to detect changes in performance or mood which may serve as an alert in combination with other sensations of hypoxia.

This is key in maintaining situational awareness.

DANGER

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Key Point: Facial pallor is an early sign of cyanosis, which again is a significant warning of danger.

Signs

Cyanosis Cyanosis is where our fingernails and lips turn blue from lack of oxygen.

This is best noticed when looking at our fingernails which are semitransparent to the blood stream. Normally, well oxygenated blood is a bright red or pink in color. As less oxygen is bound to our blood cells we begin to lose this rich color as it starts to fade to a bluish tint. This is cyanosis.

Usually by the time we recognize cyanosis we are very hypoxic. The goal of this book is for you to be able to identify hypoxia before you become cyanotic. There are numerous sensations that should be recognized well before the development of cyanosis. If you happen to notice cyanosis in your fingers while in flight you are dangerously close to losing consciousness, even if you feel your symptoms are minimal otherwise.

Facial Pallor The Pilot Who Saw a Ghost

Obviously we can’t see our faces turning white but we certainly can notice it in our crew members or passengers. Facial pallor is the loss of color in our face, especially our lips which can turn blue. The face is rich in blood vessels. Watch any hocky player who gets a facial cut out on the ice. It is usually quite dramatic.

Usually our faces have a rich rosy color to our cheeks due to the rich blood supply. When we become upset or excited our faces can easily “ blush”. In hypoxia, our faces begin to lose that color. They will appear to be pale as if not feeling well or having seen a ghost. This is a variation of cyanosis reflecting advanced hypoxia. Immediate action in donning the mask is essential here as we are very close to incapacitation.

Key Point: Cyanosis is a critical warning sign and there should absolutely be no delay in donning of the mask.

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Signs

Tremor The Shaky Pilot

Another sign of hypoxia is that of tremor. It usually occurs as hypoxia reaches a moderate or advanced stage shortly before incapacitation ensues.

The tremor is mostly noted while using our hands as compared to that at rest. It is most easily noted when reaching out to change your instrumentation. The hand will feel weak and shaky. Often we will reach past the instrument or fall short of reaching it, clumsiness if you will.

Fine motor control of instrumentation becomes very difficult such as rotating a knob or lightly adjusting your throttle or yoke.

As hypoxia worsens the tremor becomes more jerk like in nature. This is known as myoclonus and is ominus! You or your crew member are seconds away from losing consciousness.

Key Point: Tremor represents an advanced sign of hypoxia. Immediate donning of the mask is needed.

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Signs

Change in Peformance of Your Crew Member

As we’ll soon discuss in the mental impairment section a significant sign that you will notice is a sudden change in the performance or behavior of your crew member.

Assuming that you know your crew member fairly well it is easy to detect a change in his or her performance. Subtle

changes can include less fluent conversation, delayed response

times in normal ATC communications, forgetfullness such as having to repeat phraselology several times.

Other examples include a sense of aloofness- as if they are daydreaming. Staring out the window when noemally they would be focused on flight. Or a change in mood such as sudden inappropriate euphoria and speech that is out of keeping with normal phraseologyl on the flight deck.

Figure 6: Advanced Crew Resource Management as it pertains to Hypoxia.

Key Point: The better we know our crew members the easier it is to detect early subtle changes in behavior, performance, or mood.

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Signs

Neurocognitive Impairment A House of Cards

The fact that you are reading this book I can safely assume you are very intelligent. You studied hard to pass your exams and performed very well during simulator training. Congratulations by the way on your fine accomplishment and isn’t it a wonderful skill to be a pilot. I need to remind you that all that brain power was fueled at sea level by a rich supply of oxygen. Well you can just throw some of that intelligence out the window along with your cabin pressure as the available oxygen to fuel that smart brain of yours is rapidly diminishing. The brain is highly dependent on a constant source of oxygen and it shows quickly as we ascend into the higher altitudes. Initially, the impairments are subtle but quickly accelerate to incapacitation, hence “The House of Cards”. So it behooves us to invest some time to understand this phenomenon. Some examples of neurocognitive impairment include:  Loss of Multitasking- Fixation  Loss of Short Term Memory  Visual Confusion  Delayed Response Times  Disturbed Speech  Poor Motor Skills  Unable to follow simple instructions

Key Point: Neurocognitive impairment can be difficult to identify as it ultimately results in fixation and subsequent incapacitation.

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The Hypoxia Fingerprint

Before we begin looking at the different profiles of hypoxia we must know that each person reacts differently to hypoxia. It is as unique as the person’s “fingerprint”. Even though there are many similarities the experience is unique to each pilot.

Each person can have different sensations and signs. Each person may have a different time of useful consciousness (TUC- discussed later).

Some people will have many sensations but continue to perform flawlessly right till the point of loss of consciousness (LOC). Some people will have no sensations but begin to lose control of their aircraft. Some people will be communicating fluently and then as if there was a light switch suddenly turned off, begins to stare and is no longer responsive. Some people will have numerous sensations, slurring of the speech as if drunk but continue to perform flight smoothly where as another will stall his aircraft and not seem to care.

So the patterns are numerous and unique. Each pilot

should know his or her pattern as well as their crewmembers which increases the probability of early identification.

Even the most experienced of us can miss this potentially fatal scenario. Remember that a pilot has a unique fingerprint and can manifest any combinations of these impairments.

Key Point: Each person is unique and the patterns can change over time with age.

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The Spectrum of Hypoxia I want you to think of hypoxia as a spectrum. The characteristics are dependent upon the ascent rate and maximum altitude. So this is a dynamic process and the characteristics are not all the same.

Let’s begin with an explosive decompression (seconds to less than 1 minute) at an altitude of 40,000 feet. There isn’t enough time to appreciate how the brain slows down as Loss of Consciousness (LOC) can occur within 10-15 seconds. Here the rate of ascent was extremely fast.

Rapid decompression at these altitudes (2-3 minutes) tend to be sensation dominate and more easily noticed resulting in immediate situational awareness and the subsequent donning of the mask.

Slow onset hypoxia (10-15min) may be the most dangerous profile due to less intense sensations allowing for significant neurocognitive impairment to occur resulting in fixation and then incapacitation.

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Very slow onset hypoxia is relevant to general aviation. High altitude unpressurized aircraft that require oxygen supplementation above the altitudes of 10,000 feet is particularly prone to hypoxia if oxygen is not properly supplemented.

Even long term exposures of commercial cabin altitudes of 8000 feet can have an effect. Even though considered to be within the normal range of physiological acceptance some people are vulnerable to the low normal range of oxygen when prolonged over many hours on a long haul flight.

Indeed, most fatal events occur due to slow onset hypoxia as situational awareness is lost as we fixate and lose our ability to multi-task.

Key Point: It is important to see hypoxia as a Spectrum that is dependent mostly on rate of cabin altitude ascent and maximum altitude exposure.

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The Spectrum of Hypoxia

Time of Useful Consciousness (TUC)

Take the time to memorize this table. Consider it a task such as learning your multiplication tables. It is well worth your time to do so. It could save your life. Appreciate that hypoxia starts above 5K where it can reduce your color vision after 30 min of night flight. Appreciate that above 10K we can feel the slow effects of hypoxia even after 1 hour. Know that TUC at 18 K is only 30 minutes or less. Look how quickly TUC’s

dramatically reduce above 18K as you approach 25K- only 3-5 min! And once above 30K we are in very dangerous territory and as we approach 40K we only have 10-15 seconds. This table should be memorized and you should always be humble to the potential consequences of a cabin depressurization. Keep in mind that this table is an approximation at best and that each pilot is different. Remember the hypoxia fingerprint. It is also based on seated positions at rest. If excited or engaged in movement of any type the TUC’s are significantly less. Do NOT assume at 25K that you have plenty of time before you need to put your mask on! We never wait till the end of the TUC to don our masks!

Altitude Time of Useful Consciousness

43,000 8 – 12 Seconds 30,000 30 – 60 Seconds 25,000 3 – 5 Minutes 22,000 4 – 8 Minutes 18,000 30 Minutes 14,000 60 – 70 Minutes 8,000 Upper Limit 5,000 Color Vision

Sea Level Infinite

Key Point: There is no time to lose at any altitude. Your immediate action in any altitude decompression is to immediately don your mask! It is so much easier to solve a problem when you are conscious rather than unconscious.

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Spectrum of Hypoxia

Explosive Decompression

The picture of hypoxia here is much different than a slow onset model. This is a dramatic and near violent event that encompasses more than hypoxia. If the explosive decompression occurs at 40,000 feet, then the TUC is 10-15 seconds. Hence, you should show proficiency with your mask by donning with one hand in 5 seconds. Can you do it? I suggest you practice and build muscle memory. (Like a quick draw at the OK Corral!). Also, consider which hand is dominant. Practice donning in both the left and right seat. Look to see what is easiest for your dominant hand. It may not be as easy as you think. Practice makes perfect!

Standard Cabin Pressurization

Rapid or Explosive Decompression

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Spectrum of Hypoxia Assuming you successfully donned your mask there are other issues to be aware of. The first is that of trapped gases where there is an explosive expansion of air within all body spaces. This would include your middle ear, sinuses, abdomen and lung spaces. Significant pain and even bleeding could occur. Your immediate action after donning your mask is to descend as rapidly as possible. So the descent is not only to satisfy oxygen availability but also to recompress the air within your body cavities to reduce pain and discomfort. Last but not least, it is quite possible that you might experience decompression illness (DCI) even if you don immediately. Review the above illustration to understand that saturated Nitrogen gas in your tissues will erupt out of solution as bubbles causing pain mostly to your large joints, spinal cord and brain. The treatment is the immediate donning of the mask with 100% Oxygen and maximize the descent to decrease the size of the bubbles.

Rapid Decompression 1-3 minutes

When a rapid decompression occurs over 1-3 minutes the effects of trapped gases are easily noticed. Your ears will “pop” frequently and you may notice sinus pressure or pain. Also easily noticed are the initial sensations of hypoxia. It comes over you quite strongly. In this profile dizziness is very common with strong sensations of numbness or tingling over the hands and feet. Most chamber programs in the United States emphasize this profile. In those programs, pilots remain on their masks up to 25K. At that point they remove their masks and the hypoxia sensations come on quite strongly over 3-5 minutes (often less). The key point here is that identification should be easy for you and your immediate action is to don your mask. However, review of accident cases finds that fatalities rarely occur in explosive or rapid decompression events. The dynamic changes in the cabin environment maintain situational awareness and most events result in the early donning of the oxygen mask followed by a successful and safe emergency landing.

Key Point: Explosive decompression is extreme requiring donning of the mask in 10 to 15 seconds.

Key Point: A TUC of 3 to 5 minutes does not mean you can wait that long before you need to put your mask on!

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Spectrum of Hypoxia

Slow Onset Hypoxia 10-20 Minutes

The Most Dangerous of All Scenarios

SAMI has flown over 3000 pilots in this model for training purposes and it is safe to say that the very best of us can be lured into incapacitation regardless of our experience and skill. Review of the accident reports over the past 17 years finds that all fatalities due to hypoxia are related to slow onset models. Most of these events were failure of pressurization on the climb out! While busy multi-tasking with takeoff procedures and with the perception that you are not high enough to worry about hypoxia is a fatal setup for catastrophe. The 3000 pilots that have flown this profile at SAMI were provided flight simulators to realistically create a flight scenario while the cabin altitude rose slowly over 10-15 minutes at a rate of 1,5000 to 2000ft/min. The predominate finding was the loss of situational awareness as they became fixated trying to fly their aircraft. By the time they experienced 3 sensations of hypoxia they were significantly impaired and often needed help donning their mask. Whether beginning cadets or experienced corporate jet pilots the pattern remained the same. We can all succumb to this most

Statistically if we are going to die from a hypoxia event it will most likely be this scenario.

So it behooves us to study this profile with more detail.

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Spectrum of Hypoxia dangerous scenario and hence we need to identify this situation earlier rather than later. By the time you call out your 3rd symptom, it may be too late. If you only remember one thing after reading this book, then please remember this: a failure of pressurization on the climb out while task oriented or task saturated is the most dangerous of hypoxia scenarios and has the highest probability of fatality. I can bet the farm on this as I have personally observed 3000 brilliant pilots who became less brilliant as a function of altitude. Following are representative cases to help you better understand the dangers of slow onset hypoxia along with some pearls that can save your life.

Key Point: Early identification of Slow Onset Hypoxia is essential!

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Spectrum of Hypoxia

Slow Onset Hypoxia The Helios Event

If there is any event that you should study it is this. The Helios Boeing 737 event of 2005 resulted in the deaths of all 121 onboard. This case is the model of slow onset hypoxia which occurred due to a failure of pressurization on ascent. Look closely at the time sequence beginning with “wheels off the ground”. On the climb out the crew missed the fact that the cabin wasn’t pressurizing and within 13 minutes became incapacitated. The aircraft then flew as a ghost until impacting the ground in Greece. There is much more to learn from this event and it would be worthwhile to review the Greek NTSB final report. Much can be learned from this event that goes far beyond hypoxia. It may be one of the best examples of the “chain of errors” concept that can apply to all of us. So what is the TUC of a failure of pressurization on ascent in routine commercial ascent profiles? Here it was 13 minutes!

Key Point: Hypoxia is a phenomenon of takeoff and not restricted only to a high altitude decompression!

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Spectrum of Hypoxia

Slow Onset Hypoxia “The Poor Man’s Altimeter”

Fortunately, we have a built-in altimeter within our bodies that we have discovered at SAMI. Having flown over 3000 pilots in this ascent profile (Helios) we can safely say that the initial sensation of hypoxia occurs at 18,000feet (+/- 1000ft) in over 90% of the pilots. This was initially determined at an ascent rate of 1500 feet/min beginning from a cabin altitude of 5000ft. Furthermore, we were able to determine that the average oxygen saturation at the time of awareness was 73% which is remarkably low. So in other words, by the time you get your first symptom your oxygen availability is already very low and this explains the importance of early identification. So what would your first symptom or sensation be? It could be slight dizziness, mild tingling of the hands and feet, a warm flush over the chest and face, or changes in your vision. If at this point you look at the cabin altimeter it will most likely be 18,000ft. Your immediate action is to don your mask because your oxygen saturation is already critically low. Remember at the slower ascent rate profiles your initial sensations of hypoxia can be quite mild. And if you are task oriented it could easily be ignored. You are going to have to remember that you need a high index of suspicion to maintain situational awareness before you fixate.

Key Point: In regards to hypoxia, always trust your body. It is trying to warn you. In visual spatial illusion we always trust our instruments.

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Key Point: The fundamentals of hypoxia remain the same regardless of the type of aircraft we fly.

Spectrum of Hypoxia

Slow Onset Hypoxia

The Payne Stewart Event

Golfers are aware of this unfortunate event where Payne Stewart, a famous golfer, along with everyone on board died in this accident in 1999. Again, this was a failure of pressurization on

ascent where slow onset hypoxia was the primary cause of the accident. Look closely at the time sequence beginning with “wheels off the ground”. Eight minutes into the ascent there is a seemingly normal communication with ATC and the crew. Only 6 additional minutes later there is no response from the flight deck. Lights out-nobody is home.

In this case, the TUC from time of takeoff was similar to the Helios event: 14 minutes. Regardless of the type of aircraft we fly, the fundamentals of the atmosphere remain the same for all. Chances are the crew and passengers noticed their first hypoxia sensation at a cabin altitude of 18,000 feet.

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Spectrum of Hypoxia

Slow Onset Hypoxia - Solo Pilot Model “The Most Dangerous of All?”

Our last case to review was this event in Australia involving a Super King Air where there was a solo pilot flying 7 passengers. Again, there was a failure of pressurization on ascent and within 20 minutes (the ascent rate being slower than that of the Lear or Boeing 737) the pilot was noticeably incapacitated by ATC. His speech was slurred and soon became incomprehensible. Despite ATC firmly telling the pilot to put his mask on, he was unable to do so.

This further emphasizes the need to identify slow onset hypoxia early as we can be lured into a dull state of mind while focusing only on certain instruments in our fixated state. At that point it is too late.

Very Slow Onset Hypoxia (1 -4 Hours at 5-15,000ft)

This model applies mostly to general aviation, in particular the unpressurized technically advanced aircraft (TAA).

Take a look at the general flight profile of the above case. Originating in high altitude terrain the pilot already had a head start in his hypoxia even though acclimatized to altitude which by the

way does not protect us from hypoxia once we get to higher altitudes.

Here the pilot was noted by ATC to be making mistakes flying in the wrong directions and not making sense in his communications. As you can see he was exposed to altitudes of 10-14,000 feet for several hours at which point he lost control ascending to 16,000 feet followed by a dive to impact. This pattern is the most insidious of all! Again, there is the perception by some that hypoxia occurs only at the higher altitudes.

Key Point: The solo pilot must have a higher index of suspicion for cabin depressurization. The pilot does not have the benefit of crew resources here.

Key Point: Very slow onset hypoxia over several hours between 10,000 to 15,000 feet is very dangerous.

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Pulse Oximeter Report of Dr. Paul Buza flying from Orlando, FL to Dublin, Ireland.

Spectrum of Hypoxia

Commercial Cabins 6,000-8,000 Cabin Altitude - “Physiological Fatigue?”

Pilots and passengers often report feeling “wiped out” after a long haul flight. For the most part we attribute this to jet lag or disruptions in the circadian rhythm. Melatonin and cortisol are important players in the circadian rhythm which help determine our normal “body clock”. We typically think of this when we change time zones and call it jet lag. However, a recent study performed in France found that crew members felt just as tired flying North to South as much as those flying East to West even though they didn’t change time zones. It was found that there was a disruption of melatonin and cortisol in this group as well and that it may be a function of cabin altitudes.

Early studies performed at SAMI by using continuous physiological monitoring of the oxygen saturations and heart rates during long haul flights are quite revealing. The observation is that our oxygen saturations decrease more than we would expect even at presumed normal cabin altitudes.

Oxygen saturation is very important to us physically as we need to maintain a saturation of 92% or more to stay within our physiological range. This is no different than looking at the fuel on board your aircraft. Oxygen is the fuel for your brain and at the low end of normal (92%) it begins to decrease in performance. Sustained over long periods of time such as 8-15 hours on long haul flights, it can be expected to contribute significantly to fatigue- “Physiological Fatigue”.

As an example, take a look at the average oxygen saturation during a 7-hour flight from Orlando to Dublin where the cabin altitude was maintained at 7,500 feet for the majority of the flight. You can see that the average saturation was 91.65% and often dropping as low as 81% during a nap. This gives further concern about the quality of a scheduled inflight nap to combat fatigue as our breathing becomes irregular during sleep.

This completes our discussions on the spectrum of hypoxia. Hopefully by now you have a better picture of the different scenarios of hypoxia as a function of ascent rates and maximum altitude.

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Spectrum of Hypoxia

The Sequence of Hypoxia Now that you are becoming quite the expert in cabin depressurization scenarios why stop here? Let’s advance our knowledge even further by learning the sequence of hypoxia.

Let’s take advantage of the trapped gas

phenomenon to identify cabin depressurization. Why wait till our first sensation of hypoxia (18,000 feet)?

As you can see in the diagram above, the first effect of decreased cabin pressure is the expansion of air within our cavities, especially our ears. As we ascend we often notice frequent “ear popping”. This is a most valuable clue! In over 3000 pilots flown in this model over 90% of pilots noticed frequent ear popping while ascending from a cabin altitude of 5000 feet up to 18,000feet. Other words, you should be able to identify a slow cabin depressurization well before your first hypoxia sensation. Why wait!

In approximately 20% of the pilot group there was a noted abdominal bloating sensation along with the frequent ear popping. So if your ears are popping frequently and you have the sudden urge to practice the Free Air Release Technique” you might want to take a quick look at your cabin altitude! Furthermore, when a gas decompresses it tends to cool. So if you also notice that the cabin temperature is cooling along with your ears frequently popping this is highly suspicious of an early decompression. Again, why wait?

Take a moment to look at the sequence illustrated above to see the expected sequence as a function of altitude.

Key Point: Trapped gases are your first clue to hypoxia even before it occurs! Know the sequence for early identification!

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Spectrum of Hypoxia

The Clues of Hypoxia and Boyles Law

It’s not enough to just know our symptoms. We need to see the bigger picture as much is happening amongst the crew. There are so many clues to cabin depressurization why not use them all.

The more clues that we are aware of increases our chances to identify situational awareness.

So these clues can be broken down into 3 main categories:

1. Sensations (symptoms) – that what we can feel including trapped gases 2. Signs- that what we can see in ourselves and others 3. Neurocognitive impairment- lack of performance or change in behavior

Key Point: Knowing all the clues of depressurization results in early identification.

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Crew Resource Management Communicate Before You Fixate

Thus far we have studied models emphasizing the importance of early recognition of hypoxia within ourselves. However, we do not fly solo most of the time so why not take advantage of multiple members who are feeling the same way as you at about the same time!

Crew based physiological training increases the statistical probability of earlier identification. Take a look at the chart above and appreciate that if 3 or 4 crewmembers (including flight attendants) begin to have several sensations of hypoxia that the total number of clues among the crew is dramatically increased! If 4 crewmembers identified 4 clues each that results in 16 clues! Compare that to the solo pilot who might become incapacitated after 3 or 4 clues. This represents a mathematical fourfold increase in establishing situational awareness.

This assumes that the crew members freely communicate for if they didn’t, we then have 4 isolated crew members on the same flight. Otherwise this represents a significant waste of talent and training.

Key Point: Communicate before you fixate.

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Crew Resource Management

Flight Attendants Potential Heroes

Flig

Flight attendants are more than twice as physical as the seated pilot. They are consuming more than twice the amount of oxygen compared to the seated pilot. Think about it: they are standing, talking, walking quickly up and down the aisles, bending down to get that Diet Coke, not to mention pushing a heavy cart. In a silent slow decompression, they will be the first to feel the effects of hypoxia!

The effects of hypoxia are the same for all on board regardless of their station. The first person to notice the effects should trigger communication to establish situational awareness.

In the unfortunate Helios event, one of the flight attendants was a trained commercial cadet pilot waiting to be hired. As the aircraft failed to pressurize the passenger oxygen masks deployed. The first expectation is that the aircraft would level off and then descend which it didn’t. The crew, now incapacitated did not respond to the attempted calls by the flight attendant. As the aircraft continued to ascend he could have made the decision to go into the flight deck where he would have found the hypoxic crew. If he had put their masks on they would have quickly recovered and thereby prevented the catastrophe.

Key Point: All onboard can play an essential role in the event of a cabin depressurization, even passengers.

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Crew Resource Management

Hypoxia Mask Recovery The One Minute Rule

How long does it take to recover from hypoxia?

The answer lies within 2 categories: 1. The awake but very impaired pilot 2. The unconscious pilot with closed eyes

For the impaired but awake pilot the recovery is almost immediate within 15-30 seconds. It is dependent on the number of breaths he or she takes on the mask. Usually within the 3rd or 4th breath you will see a noticeable change as the eyes brighten up and often the pilot resumes flying unaware of how hypoxic he or she was!

A recent study at SAMI found that the average time to full oxygen resaturation was 60.13 seconds. This is so reliable that we call it the “One Minute Rule”. Incorporated into our advanced CRM training program we now include this as a cross check that the crew members should do approximately 1 minute after donning of the masks. So the scenario is immediate donning of the mask, descent of the aircraft and declaration of the emergency followed by the cross check of recovery. If a crew member does not seem to be normal again after 1 minute, it is imperative to check the fitting of the mask to ensure maximum flow. Do not wait!

For the unconscious pilot it will take a little bit longer. In the unconscious state our breathing becomes irregular. So you can hasten the recovery by stimulating the pilot by firmly pressing or pushing on the chest. This will result in a startle like reflex accompanied by a deep breath and almost immediately they will wake up. Usually, this process occurs within 30-60 seconds. Once again, they will want to resume flying and often are unaware that they even passed out! If the pilot was unconscious for an extended period of time, allow more time for recovery.

So what is your expectation as to how long it will take for yourself or a crewmember to normalize once they don their mask? The answer is almost immediate and if not, the mask most likely is not fitted properly with a leak. Remember the 1-minute rule.

Key Point: Check the mask fitting if you do not see a near immediate recovery.

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Crew Resource Management

A Word About Children

Infants and young children under the age of 5 have immature Eustachian tubes as their skulls are still growing. This makes it difficult to equalize the middle ear naturally and is also why they are prone to frequent ear infections.

Let’s remember that the greatest net change in gas volume occurs closest to sea level. So a descent from 8000 feet down to sea level may be easy for us to manipulate with the Valsalva technique, but not for our little ones.

Remember that it is easy for us to ascend as the middle ear acts like a one-way valve. Our problem is when we descend and air cannot re-enter the very small Eustachian tube. So in the final phase of descent the pressure is building up quite significantly pushing the ear drum inward. This can be very painful for the little one!

So be mindful of the happy baby during flight that suddenly starts to fuss during the descent and then begins to cry. This is a middle ear squeeze till proven otherwise. The solution is for baby to swallow and or suck on a pacifier that often helps open up the Eustachian tube.

Another consideration is that of the colicky baby who tends to fuss due to abdominal gas. As the cabin altitude ascends to 8000 feet there is a significant expansion of the trapped volume of colonic gas. A colicky baby at sea level can become very agitated at cruise altitude.

Key Point: Infants are not immune to the effects of trapped gas during routine commercial flights.

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Crew Resource Management

Night Time Cabin Depressurization

Almost all reported events of cabin depressurization have occurred in the daytime.

What if the cabin depressurization occurred at night? How would the experience of hypoxia be perceived to that of daytime ambient lighting?

In the night time lighting environment it would be harder to notice cyanosis of our fingernails and or the facial pallor of our crew. We rely more on auditory conversation as our peripheral vision is reduced. We tend to focus more on the highly contrasted lighting of our instruments resulting in higher degrees of fixation.

At SAMI we have begun night time hypoxia flight profiles with the intention to identify yet another potential scenario of hypoxia.

Key Point: Nighttime decompressions may be harder to identify.

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Crew Resource Management

Who Is Your Best Friend?

Well that would be your oxygen mask.

Do you take the time to practice the mask? Can you don with 1 hand in 5 seconds? Have you worn the mask for at least 15 minutes finding out that it can be quite uncomfortable? Can you communicate with a busy ATC controller while descending? Will you remember to Valsalva with the mask

while attending to an emergency? Is your mask setting in 100% mode? If you were terrain limited would you be able to calculate your oxygen and fuel reserves with the mask on?

Practice makes perfect.

We recently integrated a Garmin 1000 system with Zodiac Aerospace EROS masks into the high altitude chamber program and quickly realized the deficiencies that many pilots have in regards to their mask skills. As a result, we have quickly adapted our training program to satisfy the above questions through intensive mask training.

I strongly recommend that you and your crew periodically review the details of the mask along with potential cabin depressurization scenarios you might encounter.

Key Point: The one time a rare cabin depressurization occurs is not the time to practice your mask!

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Summary Pearls to Remember

By now you should a broader view as to the importance of hypoxia awareness. Please be aware of the fact that hypoxia is “100% Preventable”. Through training and practice along with your alert systems you are in full control of this dangerous emergency. You should now have the confidence to manage these scenarios. I will leave you with the following pearls:

• Hypoxia is highly variable and unique to each pilot- The Hypoxia Fingerprint.

• The hypoxia experience is different depending on the rate of ascent- explosive vs. slow

Know your scenarios. “The Spectrum of Hypoxia”

• Trapped gases will be your first clue even before you feel your first hypoxia sensation

Know the “Sequence of Cabin Depressurization

• Know the 3 categories of the “Clues of Hypoxia”, not just the classic signs and symptoms.

• Know that slow onset hypoxia is the most dangerous of all scenarios

• Early identification is essential! Do not hesitate to don your mask.

• Cross train with your crew. Review depressurization scenarios together.

• “Communicate Before You Fixate”

• Trust your body as it is trying to warn you of hypoxia “The Poor Man’s Altimeter”

• Know that recovery by donning of the mask is almost immediate.

• Know the “3 D’s”- Don-Descend-Declare followed by cross checking your crew after 1

minute.

Good Luck and Remember:

Protect Thy Brain and Oxygen is Your Friend

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Appendix

Although not directly related to hypoxia I included a short discussion of key topics that may assist you in avoiding fatigue and incapacitating medical conditions. Optimizing our sense of alertness and avoiding distractions is crucial to every flight.

Sleep and Fatigue

Fatigue is one of the most significant concerns in aviation today. There are many contributing factors to fatigue:

1. Inadequate sleep - Just because you close your eyes for 8 hours is no guarantee that you obtained quality sleep. Sleep is a physical need, no different than the water and food that you need on a daily basis. If you do not feel refreshed after a night’s sleep you probably didn’t get good physiological sleep. If this continues over time you may need to see your

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physician to determine if you have a sleep disorder. Sleep disorders are very common and often go undiagnosed.

2. Stress - Is the world we live in today. Our occupations, social lives, and the internet world can be overwhelming. Chronic daily stress disrupts sleep patterns and results in fatigue that can lead to exhaustion. Learn to manage and mitigate your stress.

3. Jet Lag - Disruption of our circadian rhythms makes it difficult to get back to a normal sleep cycle. Although beyond the scope of this book it would be beneficial for you to research this phenomenon and learn how to mitigate its effects.

Medications The FAA has strong guidelines on the use of medications and flight, and for good reason. Medications often have side effects that can occur unexpectedly resulting in debilitation in the flight deck.

Any new prescription medication recommended by your physician should also be considered further as to the compliance with the FAA regulations. Obviously your health is of top priority and depending upon the condition that is being treated; further consideration with your AME should be discussed in reference to fitness of flight.

Over the Counter Medications (OTC’s)

OTC’s are not benign!! Many have the potential for significant drowsiness and dizziness. In general, you should avoid any new medication 24 hours before flight. Even health supplements and certain vitamin preparations can have potential side effects if taken in higher doses.

The general rule is that if you are in need of an OTC you should allow yourself at least 24 hours before flight to insure that there are no side effects.

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Exercise - The Magic Pill Exercise is truly the “ magic pill” of our time. Find a sport or regimen that you truly enjoy and be creative in finding the time during your busy and often erractic schedule to ensure it becomes part of your routine. At first it may be very difficult to get started but once you do, you will become” addicted” to it. And this addiction is a good thing. If you do not routinely exercise, this would be a good time to shop around and try different sports or exercise equipment

The minimum per week to obtain healthy benefits from exercise is approximately three 30 minute sessions that result in a vigorous exercise that requires a cool down period.

The benefits are outstanding:

1. Reduces stress 2. Promotes better sleep patterns 3. Maintains proper weight 4. Reduces the chances for developing diabetes 5. Reduces the potential for high blood pressure 6. Reduces the potential for high cholesterol and lipids 7. Improves stamina and decreases potential for daytime fatigue

As of yet I am unaware of a pill that can accomplish as much. And even if there was, wouldn’t it be more fun to go out and play basketball with your friends?