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Comment by bdcravens | Hacker News Reader

The most painful thing I've experienced medically was an arterial blood draw to measure my o2 sat levels. (They numb your inner wrist with novocaine then go in with a giant needle to the artery deep in there. If it's that painful numb, I can't imagine what it'd be like otherwise.

And each time it was no more accurate than the pulse oximeter.

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Most of the time we don’t numb patients to be honest. I’ve had it done to me, we practiced on each other in Med school. It is painful, but I suspect the Novocain you got didn’t work because it’s the artery that’s painful not the skin.

But it does give you different information than a pulse ox. For example, people can have respiratory failure from too low oxygen (captured on a pulse ox), but also from top high CO2 (not measured on pulse ox). It also gives a measure of acid-base status, which can be thrown off for a variety of reasons (usually renal or respiratory). It is used somewhat too much in my opinion but can be life saving in some situations.

An Pulse Ox and ABG are not interchangeable exams, with the ABG giving a lot more data about respiratory and metabolic derangements. A pulse ox can also be outright fooled such as in cases of carbon monoxide poisoning or essentially wrong in other poisoning. Also for a wrist ABG there’s no reason to use a giant needle. A 23g is usually fine, length is usually not an issue as the artery is actually quite superficial. For reference, an 18 gauge is the smallest that might be considered “large”. And the sizes are bigger as the number gets smaller.

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