Oxymetry.

[W.J. \(Bill\) Dean \(U.K.\).]

Peter Saundby has put the following posting on the U.K. u.r.a.s.:

Following the string on oxygen systems, pilots intending to fly at altitude
should be very wary of relying upon oxymetry devices intended for clinical
use to confirm in the air that they are adequately oxygenated. Professor
John Ernsting, long of the RAF Institute of Aviation Medicine gave a
presentation on their limitations at the recent International Congress of
Aerospace Medicine in Warsaw. These devices have been used by pilots of
unpressurised aircraft to monitor the adequacy of their oxygen supply or to
assess the performance of emergency oxygen systems. The problem is that
when suffering a degree of hypoxia there is a tendency to hyperventilate and
the consequent reduction of carbon dioxide will increase the stability of
oxy-haemoglobin. While blood saturation appears adequate, too little oxygen
will be released to the brain. This theory was confirmed by experiment in a
chamber; therefore extreme caution should be exercised when using oximetry
at altitude because it can offer a false assurance.

Hypoxia is a real hazard in aviation, witness the recent accident to an
airliner in Greece. Systems must be used within manufacturers guidance and
above FL245 any problem can be rapidly lethal.

Peter Saundby

Peter Saundby is a Retired Air Commodore RAF Medical Branch.

He has been the BGA medical adviser since the 1960s.

He has been a glider pilot for longer than most of us care to remember,
first with the RAF and currently at the Black Mountains Gliding Club,
Talgarth.

He is a qualified RAF pilot.

I would think very hard indeed before ignoring his advice on aero-medical
matters.

W.J. (Bill) Dean (U.K.).
Remove "ic" to reply.

[Paul Remde]

Hi,

Please define what an "oxymetry device" is.

Paul Remde

"W.J. (Bill) Dean (U.K.)." > wrote in message
...
> Peter Saundby has put the following posting on the U.K. u.r.a.s.:
>
> Following the string on oxygen systems, pilots intending to fly at
> altitude
> should be very wary of relying upon oxymetry devices intended for clinical
> use to confirm in the air that they are adequately oxygenated. Professor
> John Ernsting, long of the RAF Institute of Aviation Medicine gave a
> presentation on their limitations at the recent International Congress of
> Aerospace Medicine in Warsaw. These devices have been used by pilots of
> unpressurised aircraft to monitor the adequacy of their oxygen supply or
> to
> assess the performance of emergency oxygen systems. The problem is that
> when suffering a degree of hypoxia there is a tendency to hyperventilate
> and
> the consequent reduction of carbon dioxide will increase the stability of
> oxy-haemoglobin. While blood saturation appears adequate, too little
> oxygen
> will be released to the brain. This theory was confirmed by experiment in
> a
> chamber; therefore extreme caution should be exercised when using oximetry
> at altitude because it can offer a false assurance.
>
> Hypoxia is a real hazard in aviation, witness the recent accident to an
> airliner in Greece. Systems must be used within manufacturers guidance
> and
> above FL245 any problem can be rapidly lethal.
>
> Peter Saundby
>
> Peter Saundby is a Retired Air Commodore RAF Medical Branch.
>
> He has been the BGA medical adviser since the 1960s.
>
> He has been a glider pilot for longer than most of us care to remember,
> first with the RAF and currently at the Black Mountains Gliding Club,
> Talgarth.
>
> He is a qualified RAF pilot.
>
> I would think very hard indeed before ignoring his advice on aero-medical
> matters.
>
> W.J. (Bill) Dean (U.K.).
> Remove "ic" to reply.
>
>
>
>
>

[Ron Natalie]

Paul Remde wrote:
> Hi,
>
> Please define what an "oxymetry device" is.
>
> Paul Remde

I assume it's one of those small clip on pulseox devices
that have become popular of late. Runs about $250 and
reads out the sats and pulse rate. I have one, but I
really don't rely on it too much. Oxygen is cheap, I use
it liberally.

[Bill Daniels]

OK, but how else do you check for hypoxia? We know that self-diagnosis by
checking one's own hypoxia symptoms isn't reliable either. The US Navy
studies show that the first symptom of hypoxia can be unconsciousness.

Is Prof. John Ernsting saying, "These things don't work so don't worry about
it"? Or, "Just trust that the O2 system was manufactured and installed
correctly - RTFM and go fly high"? Maybe the millions of patients
hyperventilating due to pain and who have had a oxymeter cuff stuck on their
finger were being conned by their doctors. This isn't too helpful.

Most pilots these days fly with cannulas so hyperventilating is likely to
mean breathing by mouth thus leading to oxygen deprivation as well as CO2
reduction. Maybe pilots who hyperventilate should take a few more flights
with an instructor so they can calm down when flying.

While writing this, I got a return call from a manufacturer of oxymeters who
says that they know all about CO2 scrubbing and their laser diode sensors
take it into account as do all oxymeters as far as they know. The SpO2
readings are correct in spite of it. Nothing's perfect, but oxymeters are a
better solution than anything else.

Bill Daniels


"W.J. (Bill) Dean (U.K.)." > wrote in message
...
> Peter Saundby has put the following posting on the U.K. u.r.a.s.:
>
> Following the string on oxygen systems, pilots intending to fly at
altitude
> should be very wary of relying upon oxymetry devices intended for clinical
> use to confirm in the air that they are adequately oxygenated. Professor
> John Ernsting, long of the RAF Institute of Aviation Medicine gave a
> presentation on their limitations at the recent International Congress of
> Aerospace Medicine in Warsaw. These devices have been used by pilots of
> unpressurised aircraft to monitor the adequacy of their oxygen supply or
to
> assess the performance of emergency oxygen systems. The problem is that
> when suffering a degree of hypoxia there is a tendency to hyperventilate
and
> the consequent reduction of carbon dioxide will increase the stability of
> oxy-haemoglobin. While blood saturation appears adequate, too little
oxygen
> will be released to the brain. This theory was confirmed by experiment in
a
> chamber; therefore extreme caution should be exercised when using oximetry
> at altitude because it can offer a false assurance.
>
> Hypoxia is a real hazard in aviation, witness the recent accident to an
> airliner in Greece. Systems must be used within manufacturers guidance
and
> above FL245 any problem can be rapidly lethal.
>
> Peter Saundby
>
> Peter Saundby is a Retired Air Commodore RAF Medical Branch.
>
> He has been the BGA medical adviser since the 1960s.
>
> He has been a glider pilot for longer than most of us care to remember,
> first with the RAF and currently at the Black Mountains Gliding Club,
> Talgarth.
>
> He is a qualified RAF pilot.
>
> I would think very hard indeed before ignoring his advice on aero-medical
> matters.
>
> W.J. (Bill) Dean (U.K.).
> Remove "ic" to reply.
>
>
>
>
>

[Shawn]

W.J. (Bill) Dean (U.K.). wrote:
> Peter Saundby has put the following posting on the U.K. u.r.a.s.:
>
> Following the string on oxygen systems, pilots intending to fly at altitude
> should be very wary of relying upon oxymetry devices intended for clinical
> use to confirm in the air that they are adequately oxygenated. Professor
> John Ernsting, long of the RAF Institute of Aviation Medicine gave a
> presentation on their limitations at the recent International Congress of
> Aerospace Medicine in Warsaw. These devices have been used by pilots of
> unpressurised aircraft to monitor the adequacy of their oxygen supply or to
> assess the performance of emergency oxygen systems. The problem is that
> when suffering a degree of hypoxia there is a tendency to hyperventilate and
> the consequent reduction of carbon dioxide will increase the stability of
> oxy-haemoglobin. While blood saturation appears adequate, too little oxygen
> will be released to the brain. This theory was confirmed by experiment in a
> chamber; therefore extreme caution should be exercised when using oximetry
> at altitude because it can offer a false assurance.

Lower pH, resulting from hyperventilation, decreases hemoglobin's
affinity for O2. The rest makes sense (higher affinity, higher measured
saturation level, and yet poor O2 delivery in tissues). Could it be
*hypo* ventilation. Do you have any references we could read.

Shawn

[HL Falbaum]

How does blood vessel constriction due to cold affect the readings? The
meters usually take a bit of time to a stable reading, during which time the
glove is off. It is usually not tropically warm at the altitudes where
oximeters are most valuable.
-
Hartley Falbaum

"Shawn" <sdotcurry@bresnananotherdotnet> wrote in message
...
> W.J. (Bill) Dean (U.K.). wrote:
>> Peter Saundby has put the following posting on the U.K. u.r.a.s.:
>>
>> Following the string on oxygen systems, pilots intending to fly at
>> altitude
>> should be very wary of relying upon oxymetry devices intended for
>> clinical
>> use to confirm in the air that they are adequately oxygenated.
>> Professor
>> John Ernsting, long of the RAF Institute of Aviation Medicine gave a
>> presentation on their limitations at the recent International Congress of
>> Aerospace Medicine in Warsaw. These devices have been used by pilots of
>> unpressurised aircraft to monitor the adequacy of their oxygen supply or
>> to
>> assess the performance of emergency oxygen systems. The problem is that
>> when suffering a degree of hypoxia there is a tendency to hyperventilate
>> and
>> the consequent reduction of carbon dioxide will increase the stability of
>> oxy-haemoglobin. While blood saturation appears adequate, too little
>> oxygen
>> will be released to the brain. This theory was confirmed by experiment
>> in a
>> chamber; therefore extreme caution should be exercised when using
>> oximetry
>> at altitude because it can offer a false assurance.
>
> Lower pH, resulting from hyperventilation, decreases hemoglobin's affinity
> for O2. The rest makes sense (higher affinity, higher measured saturation
> level, and yet poor O2 delivery in tissues). Could it be *hypo*
> ventilation. Do you have any references we could read.
>
> Shawn

[Kilo Charlie]

"Shawn" <sdotcurry@bresnananotherdotnet> wrote in message
...
> W.J. (Bill) Dean (U.K.). wrote:
>> Peter Saundby has put the following posting on the U.K. u.r.a.s.:
>>
>> Following the string on oxygen systems, pilots intending to fly at
>> altitude
>> should be very wary of relying upon oxymetry devices intended for
>> clinical
>> use to confirm in the air that they are adequately oxygenated.
>> Professor
>> John Ernsting, long of the RAF Institute of Aviation Medicine gave a
>> presentation on their limitations at the recent International Congress of
>> Aerospace Medicine in Warsaw. These devices have been used by pilots of
>> unpressurised aircraft to monitor the adequacy of their oxygen supply or
>> to
>> assess the performance of emergency oxygen systems. The problem is that
>> when suffering a degree of hypoxia there is a tendency to hyperventilate
>> and
>> the consequent reduction of carbon dioxide will increase the stability of
>> oxy-haemoglobin. While blood saturation appears adequate, too little
>> oxygen
>> will be released to the brain. This theory was confirmed by experiment
>> in a
>> chamber; therefore extreme caution should be exercised when using
>> oximetry
>> at altitude because it can offer a false assurance.
>
> Lower pH, resulting from hyperventilation, decreases hemoglobin's affinity
> for O2. The rest makes sense (higher affinity, higher measured saturation
> level, and yet poor O2 delivery in tissues). Could it be *hypo*
> ventilation. Do you have any references we could read.
>
> Shawn

I agree with Shawn.....but still feel that an oxymeter is the best way of
providing info wrt your oxygen system working. I also think that within the
flight levels that most of us fly it is a clinically insignificant
difference. If your saturation is OK then there would be less drive to
hyperventilate and so it would be less of an influence. I'd like to see the
original data too.

Casey Lenox
KC
Phoenix

[John Bojack]

That should be "higher pH caused by hyperventillation"

Someone who is underventillating (not breathing) gets a lower (acidotic)
pH. due to the buildup of CO2.

We hyperventillate patients on mechanical ventillators in the OR all the
time, and still rely on the oximeters. The readings correllate very well
to actual measured blood gases, taken from an artery. It would take a lot
of hyperventillating to shift the oxyhemoglobin dissociation curve enough to
be significant. (Core Temperature is probably as important, btw)

If one is not to rely upon an oximeter.....what other convenient mechanical
means of measuring hypoxia should we rely on? Certainly, if your
oximeter reading is in the high 90's, you are OK.

One should become familiar with one's baseline readings on the ground,
btw. Normals differ from person to person due to age, cardiovascular
health...etc. A healthy, normal person breathing 21% O2 (room air at
sea level) usually shows anywhere from 97 to 99 on an oximeter.

Also, it takes a good minute, often longer, of not breathing to see a
change in oximeter readings. Conversely, there is a lag in upswing of
the readings once you start breathing again. Breathing a slightly thinner
atmosphere (at altitude) should show a slowly dropping reading as altitude
is gained, and/or more time is spent at that higher altitude. (Time at
altitude relationship, as mentioned in the FAR's regarding Oxygen use while
flying)

I guess the lesson would be to familiarize yourself with these vagaries on
the ground before using/relying upon the instrument at altitude.

It's a good numerical safety check to have on board the aircraft, but like
they teach us in training.....don't forget to also check the patient!






"Kilo Charlie" > wrote in message
news:eupYe.261468$E95.67794@fed1read01...
>
> "Shawn" <sdotcurry@bresnananotherdotnet> wrote in message
> ...
>> W.J. (Bill) Dean (U.K.). wrote:
>>> Peter Saundby has put the following posting on the U.K. u.r.a.s.:
>>>
>>> Following the string on oxygen systems, pilots intending to fly at
>>> altitude
>>> should be very wary of relying upon oxymetry devices intended for
>>> clinical
>>> use to confirm in the air that they are adequately oxygenated.
>>> Professor
>>> John Ernsting, long of the RAF Institute of Aviation Medicine gave a
>>> presentation on their limitations at the recent International Congress
>>> of
>>> Aerospace Medicine in Warsaw. These devices have been used by pilots of
>>> unpressurised aircraft to monitor the adequacy of their oxygen supply or
>>> to
>>> assess the performance of emergency oxygen systems. The problem is that
>>> when suffering a degree of hypoxia there is a tendency to hyperventilate
>>> and
>>> the consequent reduction of carbon dioxide will increase the stability
>>> of
>>> oxy-haemoglobin. While blood saturation appears adequate, too little
>>> oxygen
>>> will be released to the brain. This theory was confirmed by experiment
>>> in a
>>> chamber; therefore extreme caution should be exercised when using
>>> oximetry
>>> at altitude because it can offer a false assurance.
>>
>> Lower pH, resulting from hyperventilation, decreases hemoglobin's
>> affinity for O2. The rest makes sense (higher affinity, higher measured
>> saturation level, and yet poor O2 delivery in tissues). Could it be
>> *hypo* ventilation. Do you have any references we could read.
>>
>> Shawn
>
> I agree with Shawn.....but still feel that an oxymeter is the best way of
> providing info wrt your oxygen system working. I also think that within
> the flight levels that most of us fly it is a clinically insignificant
> difference. If your saturation is OK then there would be less drive to
> hyperventilate and so it would be less of an influence. I'd like to see
> the original data too.
>
> Casey Lenox
> KC
> Phoenix
>
>

[Shawn]

> "Shawn" wrote in message

>
>>W.J. (Bill) Dean (U.K.). wrote:
>>
>>>Peter Saundby has put the following posting on the U.K. u.r.a.s.:
>>>
>>>Following the string on oxygen systems, pilots intending to fly at
>>>altitude
>>>should be very wary of relying upon oxymetry devices intended for
>>>clinical
>>>use to confirm in the air that they are adequately oxygenated.
>>>Professor
>>>John Ernsting, long of the RAF Institute of Aviation Medicine gave a
>>>presentation on their limitations at the recent International Congress of
>>>Aerospace Medicine in Warsaw. These devices have been used by pilots of
>>>unpressurised aircraft to monitor the adequacy of their oxygen supply or
>>>to
>>>assess the performance of emergency oxygen systems. The problem is that
>>>when suffering a degree of hypoxia there is a tendency to hyperventilate
>>>and
>>>the consequent reduction of carbon dioxide will increase the stability of
>>>oxy-haemoglobin. While blood saturation appears adequate, too little
>>>oxygen
>>>will be released to the brain. This theory was confirmed by experiment
>>>in a
>>>chamber; therefore extreme caution should be exercised when using
>>>oximetry
>>>at altitude because it can offer a false assurance.
>>
>>Lower pH, resulting from hyperventilation, decreases hemoglobin's affinity
>>for O2. The rest makes sense (higher affinity, higher measured saturation
>>level, and yet poor O2 delivery in tissues). Could it be *hypo*
>>ventilation. Do you have any references we could read.
>>
>>Shawn

Oops. My bad. I was getting pCO2 (partial pressure of CO2 in blood) and
pH confused.
Hyperventilation blows off CO2/carbonate, lowering pCO2, less acid
*higher* pH (duh!), higher affinity can result in higher saturation.
Hemoglobin has higher affinity for O2 at higher pH-lungs, lower affinity
at low pH-tissues, makes sense.
Truly embarrassing, I stand (well I'm sitting actually) corrected.
I'd still like a reference though.

Shawn