High Altitude Simulations without a Hypobaric Chamber

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High Altitude Simulations without a Hypobaric
Chamber

• Controlled hypoxia under monitored conditions -
  what there is to learn

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Lecture goals

• Learn how a high altitude chamber is dangerous
  and that a safer alternative is available
• Learn how oxygen makes it from your cockpit to
  your brain and how it applies to high altitude
• Understand that we are all different, and that
  one size does not fit all when it comes to oxygen
  and high altitude

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I - The chamber ride alternative
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The past

• Can you spot the hypoxia monitor in this picture?
  
• (Hint, there are 9 of them)
• Hypoxia symptoms generally lead to neuronal damage

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The evidence is there
Brief hypoxia-ischemia initially damages cerebral
neurons. Levy DE, Brierley JB, Silverman DG, Plum
F.
Early Effects of Hypoxia on Brain Cell
Function Kreimir Krnjeviæ Anaesthesia Research
Department, McGill University, Montréal, Quebec,
Canada
- Hypoxic Encephalopathy after Near-Drowning
Studied by Quantitative 1H-Magnetic Resonance
Spectroscopy Metabolic Changes and Their
Prognostic Value Roland Kreis, Edgard
Arcinue, Thomas Ernst, Truda K. Shonk, Ricardo
Flores, and Brian D. Ross
MR images (T1-weighted with TE 20 ms, repetition
time 600 ms) showing the inferior bounds of the
typical location of the regions of interest
studied as well as the morphologic changes after
ND as detected by MRI. MRI appears normal early
after ND (A) but reveals considerable cerebral
atrophy 3 mo after ND (B).
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Modern setup

• NO ALTITUDE CHAMBER
• The subject is connected to 8 pulse oximeters for
  the 20 minute session
• He will be taken down ultimately to an 02
  saturation of 70, that is approximately 18,000
  feet
• Brain damage is unlikely due to tight control

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How we do it without a chamber

• High altitude simulation is achieved not by
  changing barometric pressure (altitude chamber),
  but by varying inhaled oxygen and nitrogen
  concentrations.

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How we control the environment

• The anesthesiologist controls the mixture of
  gases given to the subject. He is also in charge
  of resuscitation in case there is a problem
• Compare to no monitoring in a high altitude
  chamber (What I dont know wont hurt me???)

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All that can hurt you is monitored

• All inhaled and exhaled gases are analyzed
• A gold standard pulse oximeter is used by the
  anesthesiologist
• Electrocardiogram
• Blood Pressure
• Exhaled carbon dioxide
• Arterial blood gases are sometimes sampled

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Risk of Cardiac Arrhythmias

• A defibrillator is present since oxygen
  deprivation often causes irregular heartbeats
  which may lead to cardiac arrest

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Exclusion Criteria

• We exclude subjects with any of the following
  issues.
• If you are flying high, take a close look at this
  list!

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Monitoring is non-invasive

• Easy setup
• In 5 minutes a subject is ready for the test
• Duration is some 20 minutes

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An MD is in the back seat

• If an anesthesiologist were your copilot flying
  in the back seat, this is what he would be
  monitoring during your climb to the wave

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II - Oxygen From the cockpit to your brain
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How oxygen travels to your brain
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Actual Changes at Different Pressure Altitudes
Table 3. Actual measured alveolar oxygen and
carbon dioxide concentrations at different
pressure altitudes. From Holmstrom, FMG Hypoxia.
In. Aerospace Medicine. Edited by HW Randall.
Baltimore. The Williams Wilkins Co., 1971. FT
Pressure Amb O2 Alv O2
CO2 0  760 159 103 40 5000  632 133 81 37 10000  5
23 110 61 35 12000  483 101 54 34 13000  465 97 51
33 14000  447 94 48 33 15000  429 90 45 32 20000 
350 73 34 29 25000  282 59 30 27
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O2-Hgb dissociation curve
98.5 of oxygen is carried in the blood, bound to
hemoglobin
Only 1.5 is dissolved in plasma
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Curve Shifts
The curve shifts to the LEFT at altitude, because
of 1) decreased temperature, and 2)
hyperventilation that translates into lower CO2
and lower H (higher pH)
A shift to the left means the Hgb molecule will
take O2 more readily at altitude, but it will
inhibit its release into tissues (brain) even
with a normal O2 saturation
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You do not react the same way every time you fly

• Because of these variations, oxygen must be used
  early in flight to prevent accidents. A fixed
  altitude for oxygen use does NOT exist.

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Disease and O2 delivery

• Anemia
• Chronic Lung Disease
• Age
• Weight
• Heart Disease
• Carbon Monoxide poisoning

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III - Examples
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Minden Takeoff 4600
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Kingsbury grade 9000
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Mineral Peak 12500
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Boundary Peak (return) 18000
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Minden (return with O2)
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Conclusions

• Because you dont have an MD in your backseat,
  get to know yourself before you fly high
• Oxygen must be started early to prevent a
  complications from periodic variations in your
  body
• Starting oxygen early also allows you to test the
  integrity of your equipment at a time when its
  safe
• Flight physicals, even though not required by the
  FAA are encouraged in order to establish your
  risk level
• Have a backup plan if your main oxygen system
  fails
• Make sure you are breathing 100 oxygen, and not
  a mixture or something else
• Close the loop with a pulse oximeter!