When the doctor/nurse takes blood from you, why do they try to find a vein, not an artery? And also why is this mainly done on the arm as opposed to other parts of the body?
In: Biology
Doc here.
You can take from both. And the biochemistry in terms of blood gases (oxygen and CO2 content) and pH varies slightly. Some instances such as deciding on invasive ventilation and assessing respiratory function require a arterial sample.
However downside of arterial sampling is that the walls of arteries are innervated (I.e. have nerves including pain nerves in) in contrast to veins. They’re also much deeper. So taking an arterial sample is often much more painful. To the point some guidelines suggest using local anaesthetic. However in practice this is rarely done.
In regards to taking from the arm. It’s often not too painful and accessible. Other options include legs and in case of large veins in the neck (internal jugular) and groin (femoral). However larger veins require more care as often run with important structures that you don’t want to damage, such as the carotid or femoral artery.
Getting a suitable vein can get very difficult classically in IV drug users who use their own peripheral veins so much they clot off. Then I’ve seen creative placements such as even head veins (the type that bulge on typically very angry men) and veins running over the chest. To the point I once had a cardiologist boast that he’d put a cannula (the plastic tubes we put in veins to give drugs) in all the surface veins, apart from one. The dorsal penile vein. At that point all the men in the room we’re like “I’m out”
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