VBG vs ABG Confusion

Hi all, can someone help me clear this up?

From my knowledge ...
ABGs - take when want to assess PAO2/oxygen, but the procedure is painful
VBGs - can be used to take everything else (e.g. bicarb, pH, PCO2) apart from an accurate oxygenation level. It is just as quick to take/analyse (someone confirm this?)

Lactate ...
Can you measure lactate levels with both samples? Or is that a separate blood test?

Glucose ...
Same question as above (see: lactate). I'm getting a bit confused when thinking about taking glucose samples in someone who has shut-down. Oliguria maybe so no urine? I always assumed it was another coloured blood bottle, but remembered someone implying you can take it with a VBG, so again confused

Thank you

A VBG is arguably quicker to take, as you do it alongside other venous samples. If this is a first presentation in ED, you can do this when you put the cannula in. ABGs are not so painful if you use local anaesthetic. They both go in the same analyser so take the same amount of time to run.

Some blood gas analysers can also test glucose and lactate, but not all, so it's worth checking at your trust. IIRC lactate samples degrade quickly so if you are sending it to the lab you need to send it on ice and call them to let them know it's coming so they can do it urgently.

As above.

A venous lactate is indeed a huge faff so doing a blood gas is way easier, and there's very few circumstances where that would not be adequate.

Not sure what exactly you're saying about glucose but basically there are 3 options:
Finger prick (BM) - adequate in the vast majority of circumstances.
Blood gas: Sometimes gives you a blood glucose, sometimes not. Possibly slightly more accurate than above - a V or ABG certainly removes problems from things like sweat dilution, but will be more inaccurate if you delay sample processing. But if you really want accuracy for some reason you go:
Venous glucose from the lab. You do need a different coloured vacutainer (flouride - it stops residual metabolic processes from consuming the glucose).

Capillary blood gases (CBGs) are also very useful in some instances e.g. babies, COPD patients needing frequent repeat blood gases.

Thank you for the reply - v. helpful!

I suggested the use of local anaesthetic the last time I saw one done (I think I read your post about it before and it came to mind !), but I was given a look like "what are you talking about?" So I just ... stopped. Is this usually a thing only anaesthetists do because they know where the local anaesthetic is aha?

Also, what is IIRC?



Thank you and thank you for clarifying the glucose thing!

Are CBGs done as a heel prick (for babies?) And how is it routinely done for COPD patients? I don't think I've registered the existence of CBGs until now haha

IIRC = If I remember correctly.

As for the local, I was taught it at med school, can't remember if it was by the clinical skills teacher or a random doctor. It's certainly not an anaesthetist-only thing, I used it when I was an ED FY2, but it does seem to be regional - you're not the first person here to say that people seemed surprised at the suggestion. It's not hard to find out where the local is kept!

A VBG is arguably quicker to take, as you do it alongside other venous samples. If this is a first presentation in ED, you can do this when you put the cannula in. ABGs are not so painful if you use local anaesthetic. They both go in the same analyser so take the same amount of time to run.

Some blood gas analysers can also test glucose and lactate, but not all, so it's worth checking at your trust. IIRC lactate samples degrade quickly so if you are sending it to the lab you need to send it on ice and call them to let them know it's coming so they can do it urgently.

Are CBGs done as a heel prick (for babies?)

And how is it routinely done for COPD patients? I don't think I've registered the existence of CBGs until now haha

I was given a look like "what are you talking about?" So I just ... stopped. Is this usually a thing only anaesthetists do because they know where the local anaesthetic is aha?

A VBG is arguably quicker to take, as you do it alongside other venous samples. If this is a first presentation in ED, you can do this when you put the cannula in. ABGs are not so painful if you use local anaesthetic. They both go in the same analyser so take the same amount of time to run.

Some blood gas analysers can also test glucose and lactate, but not all, so it's worth checking at your trust. IIRC lactate samples degrade quickly so if you are sending it to the lab you need to send it on ice and call them to let them know it's coming so they can do it urgently.

It's worth infiltrating some lignocaine under the skin when starting out doing ABGs. Any doctor can show you how to do it - as long as it's under the skin and not in a vein/artery then it's a very safe thing to do. It's helpful when you are unconfident/unpracticed as the patient will tolerate a lot more poking around with LA. Once you're confident in always hitting the artery with a single stab, most doctors don't trouble themselves with this extra step. Some patients will also say "just get on with it" when you ask them as they'd rather have one needle (the ABG) than two (LA then ABG).

You'll see the occasional respiratory patient who insists on lignocaine because they've had so many ABGs in the past and remember the ones with LA being close to painless.

Yes



Usually an ear lobe prick. Its much less painful and often much easier.

Its only caught on in some centres so far.

I can't help but roll my eyes at these sort of comments. Do you always apply the same logic to suturing by the way?

I have applied the same logic on the few occasions when I've needed to place a single suture, yes. I personally haven't found patients to be very troubled by ABGs, although those I see usually only require a single stab, i.e. not serial ABGs. I would probably feel differently if expecting the same patient to undergo the procedure on multiple occasions.

I often give patients the choice and most just tell me to get on with it. I've not thought about using an insulin syringe before (always just a blue needle) and will happily give that a try.

Slight tangent but... My brother is an A&E reg and once claimed that there is no useful information to be gained from an ABG that you can't get from a VBG, and that the culture of requiring ABGs has very little basis in fact/need. He particularly highlighted COPD patients in A&E as an example where ABGs are cruel, unnecessary, and do nothing to inform practice. He refuses to do them. Any perspectives on this?

Are CBGs done as a heel prick (for babies?

The outreach nurses in my old hospital were an absolute nightmare - every patient they saw with a resp complaint they wanted an ABG for, and couldn't do it themselves so would essentially drag the on call FY1 behind them who had to do all their procedures. Such ABGs were rarely truly needed.

Slight tangent but... My brother is an A&E reg and once claimed that there is no useful information to be gained from an ABG that you can't get from a VBG, and that the culture of requiring ABGs has very little basis in fact/need. He particularly highlighted COPD patients in A&E as an example where ABGs are cruel, unnecessary, and do nothing to inform practice. He refuses to do them. Any perspectives on this?


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