Oxygen Use
By Brenda J. Hoilman, RN

Many people who have COPD want to know:  How do you know when supplemental oxygen is needed?  What do my PO2 and O2 Sat. tell me?

There is disagreement among many doctors as to its value and its dangers.  There are some basic guidelines............but a basic understanding of the lungs functioning is needed first.

First thing is that most people don't seem to understand the difference between the PO2 reading and the O2 Saturation.

The PO2  measures  the amount of dissolved oxygen in the blood.  The oxygen saturation is the amount of oxygen actually carried by the hemoglobin.

I don't want to get too complicated here.  You just need to know that the two measurements are not the same.  I see people with PO2 of 80 thinking it is really bad because they relate it to O2 Sat levels rather than PO2.

Here is  a comparison table of PO2 and Equivalent O2 Saturation Levels

O2 Saturation PO2
98% 100 mmHg
95% 80 mmHg
89% 60 mmHg
(supplemental O2 often suggested for PO2 of 65 or less)
84% 50mmHg
35% 20mmHg
Now that said, 70-100 is considered "normal" for the PO2

Now back to the question.  How to know when Oxygen supplementation is needed. Severe low oxygen in the blood is often associated with high CO2, and could lead to development of right heart failure in people with COPD.  Around the clock supplemental O2 is reported to benefit patients with this severe low oxygen in the blood.  But many sources say that the patient should be give no more oxygen than needed to raise the PO2 to about 65.  (including the Merck Manual, which I refer to for that guideline)  The use of oxygen without close attention to the CO2 levels could be dangerous. And that can only be determined by blood gases.  Giving too much supplemental oxygen to a person who is a CO2 retainer can cause the PO2 to rise, of course.  Too high a PO2 level tricks the brain into thinking the CO2 is ok too.  It is not.  For our diseased lungs will not remove the CO2 easily.  So, with too high level of oxygen supplementation, we can get into real trouble with the CO2 rapidly.  This could lead to respiratory failure.  Thus the suggestion from many sources that supplemental oxygen for COPD patients be kept at 2 liters per minute or less.

I know this is a little confusing.  What it boils down to is that you cannot determine whether you need oxygen supplementation.  A pulmonary doctor, armed with your blood gas information and your other info can.  Do be aware that doctors that are not pulmonary specialists often don't seem to understand the uses/dangers/guidelines for the use of oxygen in COPD.  It is just a very
special field of understanding.

Brenda J. Hoilman RN
June 1998

On November 28, 1998, shortly after this piece was writen by Brenda, she passed away. She will be missed by the many whom she helped and all those who knew her.

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