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Q. How will difference in PaO2 affect pneumonia patient?

Answered by
Dr. Sunil Kumar Nookala
and medically reviewed by Dr. Divya Banu M
This is a premium question & answer published on Sep 08, 2019 and last reviewed on: Sep 09, 2019

Hello doctor,

My father-in-law, 86 years old, has been on O2 for some time, but recently had a third bout with pneumonia. With each event he comes home sustained and comfortable on about 4 LPM, but six months prior to his most recent bout we changed the location and he has come down from 4 LPM O2 to 2 LPM, and often takes it off for half an hour at a time to eat, shower, etc., without discomfort. But after this most recent bout, the pulmonologist is saying he could not tolerate relocation back to native place. As I understand it, I think the difference in partial pressure of O2 at the alveoli would be less than 1 %. Why would that be significant?

Dr. Sunil Kumar Nookala

Allergy Specialist Pulmonology (Asthma Doctors) Sleep Medicine


Welcome to

Your relative is now in long-term oxygen therapy, the reason for that may be an acute exacerbation of COPD with pneumonia. He had around three bouts in six months indicates most probably type D COPD and he may require long term controlled oxygen therapy to further not to deteriorate.

Oxyhemoglobin curve is sigmoid in shape and his partial O2 may fall in steep part. The steep portion of the oxyhemoglobin dissociation curve is the range that exists at the systemic capillaries (a small drop in systemic capillary p(O2) can result in the release of large amounts of oxygen for the metabolically active cells and this may result in respiratory failure. So this might be the reason why your relative was advised not to shift to a high altitude.

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Thank you doctor,

To clarify, he has been on O2 since the beginning of this year, but has been able to wean off it at 6000 feet altitude over the last several months. I do understand, however, that this latest bout with pneumonia probably means we are not talking about the same set of lungs anymore.

The main thing I do not understand is where you referenced his PaO2. What do mean by this? From what I have read the PaO2 at 4500 feet is about 83.7 mmHg and at 6000 Ft 79.2 mmHg. The roughly 4.5 mmHg difference as a percentage is 0.7 %. This seems like it would be insignificant since the 79.2 - 83.7 mmHg range is on the upper horizontally asymptotic (horizontal plateau) portion of the oxyhemoglobin dissociation curve. But I understand that metric is not his, it is all of ours, that is, the prevailing atmospheric condition we are all subject to. Can you explain what you mean by his PaO2? I mean, are you saying something about his specific metabolic or biological condition is causing the standard to shift?

Dr. Sunil Kumar Nookala

Allergy Specialist Pulmonology (Asthma Doctors) Sleep Medicine


Welcome back to

What I meant when I said his PaO2 is his arterial oxygen concentration now which we can see in his ABG (arterial blood gas test). Normally, a person is prescribed home oxygen therapy when his PaO2 is less than 55 mm hg. Patients whose disease is stable on a full medical regimen, with PaO2 < 7.3 kPa (55 mmHg) (corresponding to an Sa,CO2 <88%), should receive LTOT.

A patient whose PaO2 is 7.3-7.8 kPa (55-59 mmHg) (Sa,CO2 89%) and who exhibits signs of tissue hypoxia, such as pulmonary hypertension, cor pulmonale, erythrocytosis, oedema from right heart failure or impaired mental status, should also receive LTOT. This is from ATS guidelines. So regarding your father-in-law he is already on slope portion of oxygen dissociation curve and a further decrease of 4 mmHg may deteriorate his condition.

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