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Bad ABGs when no having an exacerbation?

Does anyone else have bad ABGs even when not having an exacerbation?

It's been a few months since I had PFTs done, they were good, but at the time I was on prednisolone. Normally w/o pred (couple of year ago anyway) my FEV1 is low 80's and my MMEF is 20's-30's.

Anyway, my recent ABG's were

pH - 7.35

C02 partial pressure - 54

02 partial pressure - 27

Bicarb - 29

Oxygen saturation - 47

Funnily enough, my o2 sat on the pulse ox is ALWAYS 100%. I'll be honest, I do smoke (8 yrs) but d/t nearly always finding that it takes a fair bit of effort to breathe I've started to quit (cutting down and nearly there) ...

So yeah, anyone else have poor ABGs too?

1 Reply

Hi there,

Just in case anyone's confused, the values you've given for the partial pressures of CO2 and O2 here are in mmHg, which is the unit used in the US and Australia, among other places. In the UK we use kPa, which is why they probably look a bit strange to most people here. 1kPa is roughly equivalent to 7.5mmHg.

The pH is normal (normal range 7.35 - 7.45)

pCO2 of 54mmHg is equivalent to ~ 7.2kPa (normal range 35 - 45mmHg or 4.7 - 6.0kPa)

pO2 of 27mmHg is equivalent to ~3.6kPa (normal range 80-100mmHg or 9.3 - 13.3kPa)

The bicarb of 29 mmEq/L is a little high (normal range 22 - 26mmEq/L

As you can see, the pO2 is very low, and the pCO2 and bicarb are slightly high. This result is not compatible with an arterial sample - if you had an arterial partial pressure of O2 of 3.6kPa you would be life-threateningly unwell. The only explanation for results like this is that the sample was venous - it is relatively easy to accidentally take the blood from a vein rather than an artery.

The normal ranges for a venous sample are less clearly established than for an arterial sample - different sources give varying values. Commonly, values are around 41 - 51mmg for pCO2 and 30 - 40mmHg for pO2. pH is commonly a little lower (7.31 - 7.41 is often quoted) and bicarb is a little higher. As you can see, the results above are not far off normal for a venous sample - the pO2 is slightly lower than the reference range, but probably not significantly.

The likelihood is that this is a normal venous blood gas, but you may want to discuss it with your doctor to see if you need a repeat test to get an arterial sample.

Hope this helps

Em H


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