NOT PROCESSING O2?

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NOT PROCESSING O2? – By Mark Mangus


Hi Folks,

Again, I beg to differ with the notion that folks who cannot get their saturation to increase when
they increase their oxygen flow - even when they increase it by a LOT. First of all, if you don't
process oxygen, you die! Secondly, if you can maintain adequate oxygen saturation while sitting at
rest, then you ARE processing oxygen just fine! One thing that you must understand - and it is NOT
an easy concept to understand or keep
in mind if you don't know pulmonary physiology as well as we pulmonary health care professional do
- the saturation measurement doesn't simply tell you what your blood oxygen levels are doing - as
in "pO2". Blood oxygen saturation is a "calculation" based upon three pieces of input information:
blood pH (acidity or alkalinity of the arterial blood) AND carbon dioxide partial pressure (paCO2)
AND partial pressure of
oxygen (paO2). When you measure your saturation by pulse oximeter, you have NO CLUE what each
individual value is (unless you are using a Sunrise Medical combination CO2, O2 Saturation pulse
oximeter). The ONLY way to determine the contribution of each of those three pieces of input
contributes is to measure a blood gas. Having measured blood gases matched to saturation
measurements in hundreds of patients (especially during my very controlled research projects) I can
tell you that the desaturation that I measured when they were exercising was almost ALWAYS the
result of decreases in pH and increases in CO2 while
oxygen levels (paO2) were practically unchanged from their 'at rest' levels! That is the case with
most folks
who have advanced COPD and FEV1's significantly below 30 % of predicted, surprising as that may
seem! My bet is that for many of our members, the decrease they are seeing in their saturation is
owing to changes in "ventilation", NOT changes in blood oxygen levels.

All that said, though, the problem IS improved by increasing the flow of supplemental oxygen, kind
of in a counter-measure action. The higher you can raise the oxygen 'pressure' in your lungs, the
more you can thwart the effects of those changes. Those changes are the direct result of dynamic
hyperinflation (DH) - as I have written about many times in the past. It is a difficult concept to
understand - even for my supposedly
well-educated fellow pulmonary health care professionals. Indeed, when I discuss it with them,
often they are not even aware that it is NOT decreasing oxygen levels (partial pressure in the
arterial blood) that is causing the decreased saturation. It is adverse changes in ventilation in
the face of unchanging levels of oxygen that are reflected in the decreased saturation measurement.
Further, the changes in how the lungs work during dynamic hyperinflation include MORE than simply
worsening ventilation. There is a 'cascade' effect that includes increased trapping of air,
shifting of "where" in the lungs air goes during breathing - some areas ventilate better than
others - we call this "regional hypoventilation" - and changes in circulation within the lungs,
which becomes more and more poorly matched to where the fresh air is able to go. (We call this
"hypoxic pulmonary vasoconstriction"). The combination of these three phenomenon results in
decreased saturation as measured by your oximeter.

So, two things can improve this process. (1) You can stop and rest - which causes your breathing to
slow down and resolves DH in the process. (2) You can increase oxygen delivery to the lungs so that
more areas within the lungs actually get the oxygen which improves the circulation/oxygen matching
and improves saturation in the process. This also slows breathing which results in better matching
of ventilation to circulation. The problem is that it takes a LOT of increase in flow for MANY
folks in order to produce this effect. AND the nasal cannula is the worst device to try to do it
with. Yet, the nasal cannula is the most practical device we can use under most all circumstances
where low-flow oxygen systems are being used (By low-flow, I mean anything less than 15 L/min.)
Sometimes one of the many masks available will produce a better change with flows in the 8 -
15L/min range. But, still, systems folks have to work with rarely go that high on flow. And most
are limited in supply (LOX and Compressed gas tanks) and sill run out way too fast to be practical,
much less convenient. The only portable system that can provide high flow oxygen (8 - 12
liters-equivalent) is the Sequal Eclipse. But as many of you know, at 17 pounds, it is difficult to
handle and many do NOT consider it all that "portable"!

In any case, you CAN process oxygen just fine IF "enough" of it can be pushed into your lungs. So
the challenge remains HOW to get more into your lungs. In the mean time don't forget your pursed
lips breathing which goes hand in hand with improving the distribution of gas in your lungs,
increasing your duration of exhalation, slowing your overall respiratory rate and and helping to
reduce DH in the process.

Best wishes,

Sorry for the spacing, I had a hard time with Adobe which is the way I got it

[gerald]

I need to read it over a fe wmore times but it explains things a bit better that some of the other literature I have read. Thanks