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
We try to find a vein instead of an artery because the pressure of the blood in a vein is much lower than the pressure of the blood in an artery. This is important because the higher pressure in your arteries makes it much harder for your body to plug up the hole from the needle- you would bleed a lot more than if we poked a hole in a vein. The pressure is higher in arteries because the heart is a very strong muscle pushing the blood through the arteries to be taken all over the body. The pressure is lower in veins because little muscles all over your body are (more) gently pushing the blood through the veins back to your heart to get pumped out all over again.
Sometimes we do take blood from arteries! There are certain tests that we can only run on blood from arteries. The blood inside your veins and arteries is pretty similar, but arterial blood can tell us extra information about things like your lungs and kidneys, and how acidic your blood is. Thankfully, most tests can be run on blood from veins. When we do have to take blood from an artery, we use as small a needle as possible and hold pressure on the spot we stuck with our hand or a bandage for a much longer time. This helps the body make a plug for the hole.
We mostly take blood from the arms because they are easy to get to and usually the veins are pretty big and easy to find. However, we can take it from anywhere! I’ve taken blood from feet, stomachs, breasts, and necks when we couldn’t find a vein in an arm. We are extra careful to not take blood from people with diabetes in their legs or feet because diabetics don’t have very good blood flow in their legs, so the hole may not heal.
Your arteries are still under pressure from your heart pumping blood behind it. By the time blood gets to your veins, it’s not under nearly as much pressure.
There is a type of blood draw where an artery is punctured. But that is more specialized. An arterial puncture requires more training and carries more risks. Plus, they tend to be more painful.
Try putting a sprinkler on the end of a hose with the water turned on full without kinking it off. Next, turn down the water pressure by 50% and kink it off then try and put the sprinkler on. High pressure vs. Low pressure. Artery vs. Vein.
Venous blood goes to the heart , through the lung and then arteries. If you went into an artery, it would only go to the tissues that artery leads to which would be that effective. Also, arteries suck to stop bleeding. Veins are much easier to stop the bleeding. Also, you can blow a vein when trying for an iv and it’s not that bad. Blow an artery and you got a problem on your hands. Also your arm has lots of relatively straight veins which are easy to bang an iv into and is easy to tourniquet to get the veins to pop out. There are times when an iv is done in other spots than the arm.
Arteries are deeper in the tissue and as many have said, difficult to get to. They also have layers of smooth muscle surrounding them. If you poke them, they squeeze up and get just that much more difficult to draw from.
Veins are much easier to get at.
Pressure
Vein pressure is low and arterial pressure is high.
Drawing blood from a low pressure vein and leaving an IV catheter is safe for several days. Leaving a catheter in an artery requires a hook up to keep back pressure on the system so you don’t bleed out.
The veins in your arm are the easiest to access and the least painful place to get stuck with a needle.
_Edit: apparently the info below isn’t really relevant. I stand corrected._
You want the sharp tip to be pointed away from oncoming cells, so they don’t get impaled or otherwise damaged. The reason for veins is for convenience – the needle is inserted in the direction of blood flow, and it’s much easier to insert it away from the hand.
Otherwise the doctor/nurse would need to stand behind the patient to get the right angle.
Arterial blood is harder to get and carries more risks than venous blood and therefore is used only for specific tests.
That being said, if numerous arterial tests are required (such as being placed on a life support machine), then they insert arterial catheter so they can just open a stopcock and draw out blood required for arterial blood but can also be used for tests venous blood is used for. Arterial lines also have sensors so they can read continuous blood pressure.
They use your arm because it is easy and convenient to get at.
They use veins because they don’t want to kill you.
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